Allergies: Modern Life and Me Horizon

CHILD COUGHS

We are in the middle of an allergy epidemic.

-MAN:

-Look up, lift your chin.

One in three of us suffer from allergies like eczema,

asthma or hay fever...

-CHILD COUGHS

-Just going to do the last bit on your face.

..and they send more than 20,000 of us to hospital every year.

To find out why,

Horizon has pushed the very latest science to the limits...

..with an extraordinary experiment.

Every aspect of the lives of two allergic families

have been put under the microscope...

-BOY:

-Jasper!

-MAN:

-Aah! No!

..in order to find out why so many of us are becoming allergic.

-MAN:

-And jump! Yeah, good boy.

We've rigged our two families' homes, and everyone in them,

with mini cameras.

And we've tracked their movements with GPS.

Morning!

-CHILD:

-Morning.

We're going to follow Caroline, Freya, Joe and Danny.

JOE: This is me doing my medicines.

And Dana, Paul, Morgan and his baby brother, Jenson.

You can have some Piriton.

Between them, they have an impressive array of allergies.

I've got nuts...

I've got cats and dogs, and dust mites.

Eggs...

The...kiwi...

Avocado...

Banana.

Can you eat dairy? What about nuts and soya?

Is that everything?

-More.

-More?

-Is there anything else?

-Lots more.

-Lots more.

MORGAN SQUEAKS

Latex, dust, cats, dogs, pollen and horses?

-Yes...I think that's it.

-So quite an extensive list!

Boo! Boo! JENSON GURGLES

Extensive it may be, but it's the impact it has on their daily lives

that's both surprising and shocking.

I wash and clean and Hoover twice a day, and sweep as much as I can.

Well, literally, all of his clothing are 100% cotton

and he's got this all-in-one eczema top that covers his hands.

We had this bed built so it was much higher up,

so he wasn't at dust level.

He's also got all-in-one sort of leggings.

They even do a balaclava, but he wouldn't wear that now at his age.

As soon as he's up, out of bed in the mornings,

I have to take all the bedding off, give it a Hoover.

And he has to soak in the bath for about ten to 15 minutes.

And all his soft toys we have to wash as well,

just to make sure that there's no dust on them.

And then go in the living room and do his creams.

It is hard to fit it all in, but I think it does become

a way of life that, you know, we just get used to doing it.

Because we're following our families 24 hours a day,

we'll know where they go and what they do...

..allowing us to try and shed light on why they may be allergic.

-SHOUTS:

-Coming, ready or not!

JOE EXHALES DEEPLY

-DANNY:

-'Yeah, I've never heard of this like this, years and years ago,

'so why is it all happening now?'

-DANA:

-Ready...jump! Oh!

And it makes you wonder is there something that we're doing or

is it something that we're putting on our kids without us even knowing?

CAROLINE: 'I kind of think to myself,

' "Was it the births that could have caused his problems?"

'because his birth was quite traumatic.'

I'm convinced it might have something to do with it

cos that's the only thing I can think that I've done differently.

-CHILD PANTS

-Might be a good time to...

-Do you need your pump?

-Do you need your pump?

-I'll get his pump.

As our families search for answers,

so too are scientists around the world.

SEAGULLS SQUAWK

Scientists like Professor Syed Hasan Arshad

from the University of Southampton.

He has studied the allergic health of people across Britain

for the past 20 years.

So allergic diseases have gone up significantly

in the last three decades.

Asthma, for example, was 1% or less in the 1950s.

In the 1980s, most studies show that asthma prevalence has gone up to 10%

or, even 12% to 13% in children and about 7% to 8% in adults.

There has been a tenfold increase over a 30-year period.

Today, between 25% and 30% of people in the UK

suffer from one or more allergies,

from hay fever to asthma, eczema to food allergies.

'Allergies which used to be rare are now part and parcel

'of our daily life.'

Now, that increase cannot be assigned to genetics

because our genetics doesn't change over three decades.

It takes thousands of years to change,

so something must have changed in our environment

that influenced our genetics in such a way

that the allergic diseases developed.

But that environmental change

is specific only to Westernised countries like the UK.

The studies have shown very intriguing findings.

If a family moves from a developing world to a developed country,

the risk of allergy generally goes up.

This pattern is seen across the Western world,

from America to Italy, Australia to the UK.

One study found that immigrants' risk of developing allergies

rocketed more than threefold after living in a developed country

for ten years.

So there is something with the urbanisation,

something with the Western lifestyle

that tends to influence the risk of allergy.

In the last few years, a new theory has emerged that could help explain

why not just our families, but one in three of all of us

are becoming allergic.

Where was it?

There's got to be some deer poo here somewhere.

I can't find any now.

There's some poo of some sort there.

This is immunologist, Professor Graham Rook.

And he believes that the most prolific organisms on the planet

are behind the allergy epidemic.

Deer poo!

Micro-organisms, like bacteria and fungi.

It is calculated that the animal kingdom deposits on this planet

something like 14 billion tonnes of faeces per year.

Now, faeces contain an enormous number of bacteria

and also an enormous number of bacterial spores.

But these bacteria aren't just found in faeces.

Well, of course, the micro-organisms in bacteria in particular

are absolutely everywhere.

Even the air is full of bacteria.

I mean, there are at least, on a day like this, in this park,

I don't know...

100,000, or maybe even a million per cubic metre of air.

And if you're in the vicinity of animals,

if one were in amongst the herd of deer over there,

there would probably be... ten million.

The problem is, modern living is separating us from microbiota,

like these.

Nowadays we live in a world where those organisms

from the natural environment are almost completely absent.

You eat your squeaky-clean apple from the supermarket

and you live in a steel and glass enclosure with air-conditioning,

and you're just not encountering the right microbiota.

It's this reduced exposure to microbes that Rook believes

is impacting our immune systems and making us more allergic.

Now Horizon is seeing if the theory plays out in the real world.

CAROLINE: Right now, take it out. Do it slowly.

Then concentrate on putting it back in.

As part of our experiment, we're not only tracking our families...

CAROLINE: Very quick at that.

..we've also asked them to swab the bacteria on their bodies

and throughout their homes.

Over the coming weeks,

microbiologist Dr Lindsay Hall is going to examine the results.

What happens is that we basically take these samples,

we mash them all up and then we extract the microbial DNA.

We then put this DNA into a sequencing machine

that's able to tell us what the DNA sequence is.

We can then do some very fancy analysis on this

that then will be able to tell us exactly what bacterial species

are present in each of our family members.

So I'll know then, we'll know their bacterial communities before I actually meet them face-to-face,

so I'm really looking forward to that.

Lindsay is hoping that these bacterial communities

will give our families some answers as to why they may be allergic.

To understand this,

we need to understand what happens during an allergic reaction.

Whatever it is that triggers the response,

whether it's eggs, nuts or dust mites,

the reaction in the body is very similar.

So, first of all, I'm just going to write some marks on here.

One, two, three, ten, 11, 12...

This is consultant paediatric allergist, Dr Adam Fox.

This first one, we're actually going to use fresh milk

and also some fresh raw egg.

Today, he is using a skin prick test

to initiate a very small allergic reaction in his patient

to find out exactly what she's allergic to.

Next, we've got some tahini, which is a pure form of sesame,

all crushed up.

So, I'm just going to put a little bit of that there.

'An allergy is an inappropriate response by our immune system -

'which is really designed to protect us

'from things such as germs and viruses,'

to something that's supposed to be harmless.

For example, pollen or foods like peanut or milk,

and this can cause a whole variety of different symptoms,

some of which can be potentially life-threatening.

Let me know if it hurts - I'll be as gentle as I can.

If you are allergic to say, eggs,

when you come into contact with them,

your immune system goes into overdrive.

You OK there?

-Yeah.

-Good.

If there is an allergy, what will normally happen is

what's called a wheal and flare reaction,

which is a little itchy bump with some redness round it.

This localised reaction happens just under the skin's surface,

where in this case, the egg allergen binds to

its specific allergic antibody, called IgE...

..and this triggers the release of histamine.

The effect that histamine has depends on which parts of the body it's acting on.

So, for example, histamine in the skin will cause itchy spots.

If it's released more deeply in the skin then it may cause swelling,

something we call angioedema, and that could be quite dangerous

if, for example, it's around the tongue or the throat.

But if you're unlucky and you have a more severe reaction

that we refer to as anaphylaxis,

then it could involve difficulty in breathing,

so particularly wheeziness,

or sometimes again in severe reactions,

a drop in blood pressure and that can be very serious indeed.

In the UK, asthma attacks prove fatal for three people every day...

Mummy, Dad thinks...

..evidence that sometimes no matter how hard you try,

allergies can't always be avoided.

And as our families know first-hand,

allergic reactions can be terrifying.

It was just a normal day, I'd booked an appointment at the doctors.

My father-in-law came with me, didn't even have his shoes on.

He was just driving us in the car.

And at the time we were told he wasn't allergic to dairy

and he'd had a Mini Milk.

And literally within half an hour of waiting for the doctors, he just deteriorated.

He couldn't breathe properly.

And then within, I suppose it was seconds, I looked at him

and I could see that his lip was starting to swell.

I've never seen somebody so small with you know -

sorry for being on the camera -

I've never seen somebody so small be so sick.

Within seconds of being in the ambulance,

Joe was on the nebuliser and they kind of controlled it for me,

but it was so scary because I wasn't aware of what was going on.

Anything to do with the mouth, the airways,

could affect his breathing.

It was one of those scary moments when I thought,

"OK, this is really serious, and we have to deal with this,

"like, this could be life-threatening."

MORGAN COUGHS

Oh, dear, you're coughing a fair amount.

-Oh, darling... Oh, darling!

-Ugh..

-HE CONTINUES COUGHING

-Ohhhhh, it's exhausting, isn't it?

In recent years, many theories have tried to explain

why more children like Morgan

are suffering from allergies than ever before.

But Graham Rook believes that the evidence for them

just doesn't stack up.

It doesn't look as though it's the genes.

It doesn't look as though it's pollution.

It doesn't look as though you can explain it just by vitamin D

and lack of sunlight.

It doesn't look as though it's exposure to allergens

because people were always exposed to allergens.

So, what is it?

Something in the environment has changed that is causing allergies

to become more common.

Rook believes it's changes to the bacteria in the environment.

But this idea isn't entirely new.

25 years ago, the "hygiene hypothesis"

suggested that improved levels of hygiene and cleanliness

reduced children's exposure to bacteria and viruses,

and so, infections.

This supposedly deprived their immune systems

from the training they needed to resist allergies...

..and the idea that we were all too clean was born.

In fact, that just doesn't hold water.

Largely, one of the most important reasons for rejecting that notion

is the fact that those kinds of infection

are commonest in the inner cities, commonest amongst the very people

in whom the increases in allergic disorders are the most frequent.

It simply didn't fit epidemiologically.

Rook believes a much broader range of micro-organisms

than childhood infections are to blame.

Micro-organisms that our ancient ancestors

were continually exposed to.

Humans are really a grassland species.

Two and a half million years ago we were hunting and gathering

and scavenging in this sort of environment,

and in constant contact with the soil

and with the organisms

from the animals they were killing,

and so enormous exposure to types of micro-organism

that we simply don't encounter any more,

because we live in these concrete blocks made of glass

and steel and strange materials treated with biocides and glues.

It's changes to all of these old microbes, be they bacteria,

fungi or viruses, that is at the crux of this new theory.

We've been suggesting

that a term that could replace the hygiene hypothesis

is the "Old Friends mechanism",

because the problem is not a lack of exposure

to the childhood infections,

it's actually a lack of exposure to those old organisms

that we had to tolerate throughout our evolution.

They're the ones that provide the data that the immune system needs

to correctly set up its regulatory pathways,

correctly set up the police force that stops the immune system

from doing anything stupid.

A bit more?

Yeah. Oh, yeah, a bit more than that. Tip it in.

The Old Friends mechanism

may explain not only the increase in allergies,

but other chronic inflammatory disorders as well.

-Did it just in time.

-You did, didn't you?

And as our families continue to have

every aspect of their lives monitored,

we want to see if there's evidence for it in the real world too.

It's only in recent years that scientists have come to understand

the extent to which bacteria are a vital component of the human body.

One of the leaders in the field is gastroenterologist,

Professor Fergus Shanahan.

We call them microbes because they're tiny,

we can't see them, but they're there all right.

Most of the bacteria are on the skin, in the mouths,

in body cavities, but the vast majority are present

in the large intestine, otherwise known as the colon.

The degree to which we're covered in our bacterial associates

is staggering.

People use loose numbers to describe the vast numbers of organisms,

but it's something in the range of tenfold the number of human cells.

This is equivalent to hundreds and hundreds of billions of bacteria

in and on the human body.

Bacteria are so numerous,

they make up the bulk of living matter on Earth.

But they're not merely bystanders.

We think of bacteria generally as being something harmful,

something that could cause disease, something that could spoil food,

but the truth is

bacteria are actually predominantly beneficial to us.

They produce vital nutrients, they help us digest food

and they provide protection for us against infectious organisms.

They're an active participant in human life.

It doesn't work very well, but it's the best they've got at the moment

-cos we just don't...

-I know, that's the problem...

-Yeah...

Bacteria are now known to do so much in the human body

that they're often referred to as the "forgotten organ".

And for our families, their bacteria are no different.

Dr Lindsay Hall has brought them together

because the results from their bacterial swabs are back.

Though, unfortunately, Morgan wasn't well enough to join.

The last couple of years we've designed...

Interestingly, the first and most obvious thing

that Lindsay's discovered

is with regards to the diversity of their samples.

So what does diversity mean in terms of bacteria?

Well, if you look at this picture here,

this is a picture of our intestine

and these are all the different types of bacteria that call it home.

So, it's an unbelievably complex ecosystem.

So, if we think about ecosystems, we think about the oceans,

maybe, you know, the rainforests, things like that,

but actually, the most densely kind of colonised ecosystem

and the most diverse in the world is our gut.

The problem is, like the rest of us in the Western world,

both our families had a relatively low diversity of bacteria

in their guts...

..especially when compared to a tribe of people

who live as close to the lifestyles of our ancient ancestors

as it's possible to get.

These are the Hadza.

In the Rift Valley of northern Tanzania,

they hunt game, gather honey

and forage for berries, fruits and plants to survive.

Yeah, so I don't know if, Paul and Danny,

this is how you go out to go and get your lunch?

-SHE LAUGHS

-It's close.

It's just got... It's just got a Pret round the corner.

DR HALL LAUGHS

But it looks like tribes like the Hadza

have this high diversity of their good bacteria

and they don't have many allergies.

In one hunter-gatherer tribe,

just one in every 1,500 people had an allergy,

compared to one in three in the UK.

And it seems the diversity of microbes in the gut

is key when it comes to allergies.

It was interesting for me looking at your samples,

that Joe and Morgan had lower total bacterial diversity than...you guys.

And there's lots of studies out there that show that

individuals that have got allergies, they have a lower diversity

in comparison to healthy... healthy people.

So individuals that have got...

Not only do people in the West have lower bacterial diversity,

but those with allergies have even less.

..Allergies, and so...

And incredibly, brand-new research is proving how this lack of bacteria

may be making us more allergic.

This is Associate Professor Ben Marsland.

He's undertaken a unique experiment here in the Swiss Alps.

OK.

This is the Ecole Polytechnique Federale de Lausanne.

And the creatures that call this place home,

show what happens when you grow up without any bacteria at all.

MICE SQUEAK

These are germ-free mice.

Well, a germ-free mouse has no bacteria, no viruses,

no fungi at all, so it's absolutely pure and clean.

For all intents and purposes,

a germ-free mouse like this looks like a normal mouse.

It breathes normally, it grows normally, it looks normal.

The only difference is there are no microbes there at all.

The mice may look quite normal, but keeping them free of any bacteria

has astonishing consequences when they're exposed to common allergens.

So we took house dust mite allergens,

which is one of the most common types of allergens found in the household,

and we put them down the nose of the mice

to see what type of response they would have.

And we compared that between a germ-free mouse and a normal mouse.

The difference between the two types of mice is profound.

Some of the ways that we can measure an allergic response is by looking

at the lung tissue itself,

and in this picture we've got airways in a normal mouse

where the main air is being inhaled and alveoli around it.

So this is quite a healthy lung.

Now, if we look at a germ-free mouse,

you can see that the picture has changed dramatically.

The purple staining, which is the mucus production,

and so we know that in that setting in the absence of these microbes,

there's much more mucus production in the airway,

so it's much more difficult to breathe.

Also around these airways, we're finding inflammatory cells

and these are some of the most dangerous cells

involved in an allergic asthma response.

So with that very first simple experiment,

what we've found was that in the absence of any microbes at all,

the mice were more prone to allergy.

Normally, exposure to harmless bacteria

helps to dampen down the immune system.

So, as we get exposed to microbes,

this teaches the immune system to develop appropriately,

so that it knows how to respond against pathogens

when they are encountered.

And importantly, not respond to harmless things in the environment

like pollen or peanuts.

And if you don't have that education,

or the education is not complete,

perhaps that's why there's more of a chance to develop allergies.

Without everyday exposure to bacteria,

our immune systems can overreact.

And it seems that perhaps the most important window of opportunity

for this education, is right at the beginning of life.

It's well-documented that people who grow up on traditional farms

are often protected from allergies...

SHEEP BLEAT

..perhaps because of the huge variety of bacteria

surrounding them.

But for farmers, and in fact all of us,

it's the first year of life

that is the most critical for microbial health.

So, she's getting down now.

It starts at the moment of birth itself.

These sheep have carried their lambs for five months,

but like humans, life in the womb is very different to the outside world.

You can see she's sort of straining a bit.

Whilst in the womb, babies are thought to be

almost completely sterile, but that all changes during birth.

SHEEP BLEATS

It's all right, darling.

You ready?

In humans, the microbiota of the vagina changes before birth.

It's coming the right way.

A group of bacteria called lactobacillus starts to dominate,

bacteria that have been shown to protect against allergies.

So, as with a new-born lamb, when the baby travels down through

the birth canal, it gets covered in these bacteria from head to toe.

In effect, our first allergy-protecting microbiome

is born when we are.

But 25% of babies in the UK

are now born by Caesarean section every year.

They're more typically colonised by bacteria found on the skin

and hospital surfaces than the vagina.

This may explain why a study of 1.7 million Norwegian children

found that those born by Caesarean were 52% more likely to become

asthmatic than those delivered vaginally.

And it's now understood that breast milk contains up to 700 species

of bacteria, possibly explaining why exclusively breast-fed babies

are less likely to be allergic.

Is that funny? Whee!

But perhaps the greatest threat to children's microbes comes

when the few bacteria they do have come under attack.

As with any ecosystem, diversity is the key to a healthy gut flora.

Yet one of the greatest advances in modern medicine

is destroying that diversity...

..often with devastating consequences.

Well, antibiotics are designed

to target infectious or harmful bacteria,

which we've grown here on this laboratory Petri dish.

We put this particular antibiotic into the centre,

and you see a zone of clearance of the pathogen,

the infectious agent, and that's good.

That's a major advance that helps an awful lot of patients.

The problem with this is the antibiotic is damaging

the surrounding ecosystem.

It's killing the beneficial harmless bacteria

that we all have in our body.

The diversity of our microbes is decimated following a course

of antibiotics, not only leaving us vulnerable to attack

by other infections,

but threatening our long-term microbial health too.

The microbiome is required to educate

and help the immune system mature,

so anything that threatens the microbiome tends to create a risk

of some sort of abnormality of the immune system, and it has been shown

several times now that the greater the number of antibiotic courses

that one has, and particularly the earlier in life,

particularly in infancy, the first year of life,

the greater then the risk of allergies.

One study found that giving babies under the age of one antibiotics

increases their risk of developing eczema by 40%...

..with every extra course increasing that risk by a further 7%.

Are you watching me, Jenson?

Of course, we mustn't abandon antibiotics all together,

but if we are to preserve our microbial diversity,

doctors must be mindful

not to prescribe unnecessary courses of them.

# Gently down the stream... #

All this research suggests that modern living

is denying children today the bacteria their immune systems require.

This problem is particularly acute in those children with allergies.

Lindsay has discovered the most allergic children in our families,

Joe and Morgan, are missing some vital microbes.

One of the bacteria that actually was similar for Joe and Morgan,

in terms of it had far lower levels than what everybody else had within

the families, was this bacterium here, which is acinetobacter,

and there's some really interesting, very new studies that have suggested

that individuals that have got asthma or eczema have low levels of

this bacteria and that maybe relates to why they've got allergies.

So these are one of the types of bacteria that's able

to educate our immune system.

But acinetobacter isn't the only type of bacteria that helps

to educate our immune systems.

The furry one that Freya is holding is bifidobacteria.

You've probably heard of that

because it's in a lot of probiotic kind of drinks and yoghurts.

Look, it even looks friendly as well. That's excellent.

Thanks, Freya. Hold it up for everyone to see.

Brilliant.

It's quite interesting

because we looked at bifidobacteria levels in Morgan.

He's not got any, and Joe did have some bifidobacteria,

but at far lower levels in comparison to what you guys have got.

One study found that five-year-olds with eczema had 28% fewer

bifidobacteria as babies, compared to healthy children.

It's possible that an early life experience may have reduced

these allergy-protecting bacteria in Joe and Morgan.

Can you think of any kind of early-life events

that maybe happened to Morgan?

Well, Morgan's been on antibiotics from a very young age.

I know at about ten months, he had tonsillitis

and they gave him antibiotics.

Now, antibiotics are absolutely amazing

and we need to take them to combat infections, we need that.

But the problem is that they cause collateral damage,

so they come in and get rid of the bad guys, but again,

we're losing the good guys that are going to programme our immune system.

And interestingly, Joe's birth may well have impacted his bacteria too.

I kind of work it back to when he was born.

His birth was really traumatic.

He was starved of oxygen, he had the cord round his neck.

He was sent off and it took quite a few days for him to become

you know, become quite a normal child, as I see.

Babies like Joe

who spend their first hours of life in intensive care

can miss out on their first flush

of good bacteria from their mothers.

And it can expose them to some less friendly microbes too.

Like enterobacteriaceae.

Interestingly, if you swab intensive care units in hospitals,

this is what you find on the surfaces.

And individuals that have allergies have higher levels of this bacteria,

so that fits quite well with...

Joe's got quite high levels of this, and if that's how Joe was born,

then obviously this bacteria would maybe have colonised his gut.

Our families' results are compelling.

Clearly, there is something going on that's different to us,

but we've never really understood how things are different

internally for him, and understanding that, you know,

there's certain bacteria that both myself, Caroline and Freya have,

that Joe's lacking, it really brings it to light.

Those 24 hours are vital in the first stages

and you're not made aware of that.

You don't think about that, you know, and the first time you start

breast-feeding and then you stop breast-feeding

and you put them onto formula, you don't think about any of this.

You just think it's the natural thing to do.

I think the biggest surprise was the bifidobacteria,

where Morgan, you know...

The average person has 40 million or so in their intestines

and Morgan's got none.

'That shows that it could be a huge part of why he suffers so badly

'with the eczema and his allergies.'

Luckily, there's just enough jam left, isn't there?

With researchers from around the world studying the bacteria we rely on...

Ta-dah! Your flapjacks!

..we now have a better picture than ever before

of how the modern world is impacting our old microbial friends.

But interestingly, our lifestyles seem to be impacting

some of our old microbial enemies too.

Enemies that we've lived with for thousands of years.

Humans in Palaeolithic times

used to live in very small hunter-gatherer groups,

sometimes probably only 20 to 30 people, and so only

certain types of infection could persist within such groups.

Graham Rook calls them the old infections

and it's possible to get a glimpse of some of them here,

at the Wellcome Collection in London.

Home to a project called London's Pulse...

a collection of 120 years of medical records from 1848 until 1972,

recording births, deaths and diseases across the capital.

This one in front of me is from the Metropolitan Borough of Finsbury,

annual report for the year 1927.

And it says here, "worms".

Here's another one, 1918, East Ham.

This one, "tapeworm".

"Physis..."

"Verminus heads".

"TB in Stepney", and so it goes on.

Down here we have "threadworms" and "roundworms."

Now, roundworms, we just don't see those nowadays.

OK, this is the year I was born, so this is exciting.

"Tapeworm and TB".

As far as I know, I was never exposed to tapeworm ova,

but I could have been in 1946.

That's fantastic.

Old infections like parasitic worms and tuberculosis had to behave

in a very specific way to survive in their hosts,

be they early 20th-century Londoners or our more ancient ancestors.

One, they had to not kill the individual,

because obviously otherwise you just wipe out the hunter-gatherer group

and that's the end of the career of that infection.

And secondly, they had to be tolerated by the individual

and the individual mustn't be able to eliminate them completely.

The ability of these worms and infections

to persist in their hosts was key.

They evolved ways of quietening down the immune system,

so that there wasn't massive inflammation

causing permanent damage, and so our immune system sort of evolved to be

rather dependent upon the presence of these organisms.

So our immune system became less sensitive

and ignored the old infections.

But as a consequence, it ignored allergens in the environment too.

In effect, old infections made us less allergic.

This doesn't happen any more.

Modern health care has wiped out the old infections.

But living in groups of millions of people has allowed a new breed

of crowd infections, like measles, to take their place.

So the crowd infections,

because they either killed you or you became immune to them,

didn't evolve this ability to down-regulate the immune system.

So it's a completely different host-parasite relationship,

and of course what's happened nowadays is that modern medicine

is starting to eliminate the old infections.

We clearly don't want the persistent old infections like worms

and TB in our lives.

So what can we do to combat allergies?

Can we reverse the damage done by the modern world to our old friends?

Fergus Shanahan believes it is possible to improve

the health of our bacteria.

Two bananas, two onions.

Yeah, that's good.

And perhaps the easiest way to do this is to reconsider what we eat.

Well, probiotics are generally commercially available

bacteria in the form of a food.

People have been consuming products similar to this

for centuries, in the form of yoghurts and cheeses

and other fermented food products, so it's not novel.

These kinds of products can confer some health benefit,

but it's important not to assume that they'll also treat

a variety of non-specific claims that have been made for them.

There is some science behind these, however.

They're not completely snake oil,

but one has to be judicious in the selection of these.

The probiotics industry is now huge.

Fergus is a scientific adviser for it,

and his group at University College Cork

have even patented their own strain of probiotic.

But probiotics aren't the only tool out there to change gut bacteria.

Another way of achieving the same thing is to take something

in the food that can stimulate the natural growth

of the naturally occurring bacteria, and that would be

in the form of a diverse array of fruit and vegetables, for example.

They contain essentially what scientists called prebiotics.

These are generally of a carbohydrate nature,

so when we consume these,

we're actually promoting the growth of natural bacteria.

We're also helping ourselves in terms of the absorption

of essential nutrients.

Changing our diet with pre- and probiotics only works

as long as you keep it up, and even then, it's still not a wonder cure.

Well, there is controversy about prebiotics and probiotics,

and much of that controversy arises because of the assumption

that a single bacterium can do everything for everyone.

That's just not the case.

It's the diversity that counts.

No one food substance, no one bacterium,

no one chemical in the food is sufficient

to confer this diversity of the microbiome.

One research trial has found that giving probiotics to babies

reduced their chance of developing eczema at two years old.

But others have found they make no difference.

Whether they may help chronic health problems like allergies

remains to be seen.

Well, I don't think that prebiotics or probiotics can cure an allergy.

I think they can help prevent against infections.

I think the most important point is that the microbiota,

if it's diverse and healthy at an early stage in life when the

immune system is developing,

then you can prevent allergies occurring.

I doubt very much if these kinds of products can actually cure

existing allergies.

Surprisingly, one hope for helping those with allergies in the future

may lie in actually replacing your gut bacteria with someone else's.

This is exactly what doctors are doing to treat the aggressive

gut infection, Clostridium difficile,

and they're doing it with human faeces.

Well, the sample is weighed first, and then gently homogenised.

And this is then...sieved, for a better word...

double-sieved.

The faeces is processed in an anaerobic, or oxygen-free, chamber

to mimic the inside of the gut.

And after it's sieved, the volume is then topped up to the maximum,

so as to leave no air spaces in the bottle.

This healthy donor faeces is then transplanted into the patient,

replenishing their bacteria and curing up to 90% of infections.

It's early days and there's been no research into this technique

for allergies yet, but it may lead to a treatment in the future.

In the meantime, if we're to combat the allergy epidemic,

we must reduce our risk of becoming allergic in the first place

by re-engaging with the bacteria that's around us.

But we must do so carefully because not all bacteria are good bacteria.

So germs are everywhere in our home,

but there are places where we're more likely to find them.

Professor Sally Bloomfield is trying to educate people how best

to safely re-engage with the right microbes.

So what I'm going to do is to prepare fried chicken

and a salad to go with it.

When you take a chicken, we know that probably up to 60%, 70%

of the chickens are contaminated with either salmonella or campylobacter.

This gel mimics those germs.

So there it is, I'm going to chop it up on my chopping board

into my saucepan.

Right, so what I want to do now is I want to prepare the salad.

We may not be aware of it, but as we go about our daily lives,

our hands come into contact with all manner of surfaces,

something that becomes evident when Sally turns off the lights.

The gel, which was invisible when we put it on the chicken,

now we can see it glows under ultraviolet light.

We can see exactly where the germs have gone.

We have a look at the chopping board,

you can see that even though we tried to clean it by wiping it

with a cloth, there's still lots of germs on the surface

and on the knife.

Both of my hands are heavily contaminated with the germs.

I wiped my hands on my pinafore

and you can see I put it on my face,

so I've even got germs on my face.

And of course, the result of all of that is that you can now see

there's plenty of germs have gone into the salad, and remember,

that's going to be eaten raw.

As Sally's demonstration shows, if we're not careful,

we can very easily re-engage with the wrong type of bacteria.

So good hygiene is about recognising that there are certain

superhighways by which germs are spread,

and by which we become exposed to them,

and targeting our hygiene at those surfaces at the right time.

From thoroughly washing everything after cooking...

Where you can, rinsing germs away with running water.

And where you can't, using antibacterial sprays,

to using and binning tissues and washing your hands

after going to the loo.

There we go, let's get that under there.

Or before you eat.

But we needn't apply this level of rigour to every aspect of our lives.

Look where you're going!

The challenge is to find a healthy balance.

Pedal!

One where we nurture our good bacteria whilst protecting ourselves

from harmful micro-organisms that cause disease.

Cover your brakes.

So it's not about whether we're clean.

It's about the fact that we've become afraid of getting dirty,

of going out and engaging with our microbial world.

-Morning!

-CHILD:

-Morning!

I'm on TV!

Right, OK, so let's get your bike.

HE RINGS BELL, HE SQUEAKS HORN

Horizon's experiment is coming to an end.

And as our families relive their experience,

Lindsay has one final finding to share with them.

One which proves just how disconnected

from the microbial world we've all become.

We put GPS on all of you, and we followed you for 24 hours

to see how much time you spent indoors and outdoors.

This graph shows the 20 hours and 58 minutes

that Danny spent indoors in one day.

We figured out that it was about 85% of your time spent indoors.

But that's normal. There was a study done a couple of years ago

that showed that on average we spent about 90% of our time indoors,

which we don't really think about, do we?

I pretty much live most of my life indoors,

my work dictates that.

So that's the hours of commuting,

probably popping out at lunch

and then back in the office until I leave.

-Yeah, for your hunter-gathering?

-Yeah, that's about it, yeah.

But this indoor lifestyle has consequences

for the diversity of our microbes.

The swabs our families did of their TV remotes, kitchen tables

and floors, shows that these surfaces are covered in skin

and gut bacteria like staphylococcus and bifidobacteria.

You live inside, you share those bacteria with each other

and then you share it by kind of, you know, touching something

and then someone else comes and touches it and picks it up,

and just by personal contact and stuff as well.

And if we're inside, then we're all just sharing what we've got indoors.

And if you're outside,

you start to pick up a bit more kind of environmental bacteria.

For personal trainer, Paul...

And jump! Yeah, good boy.

..spending a lifetime outdoors does seem to have had

an impact on the diversity of his bacteria.

Look where you're going.

Really interesting, Paul, that you had loads of environmental

bacteria on your skin, but we also, when we did swabs of inside,

there was loads of environmental bacteria inside your house as well.

So you're obviously picking it up outside with your work

and then bringing it in and spreading it around.

However, as Morgan's allergies demonstrate,

no one factor is able to answer what's behind the allergy epidemic.

Though genes are important,

it's becoming increasingly clear that changes

to our environment may also hold the key to the rise in allergies,

and as scientists around the world start to discover

exactly what these changes are,

it's giving hope for children like Morgan in the future.

I worry so much about his asthma, running around too much

and overexerting himself.

Definitely taking that away with me, that I need to sort of

encourage him to be outside a hell of a lot more than what he is now.

Coming ready or not!

I think we live too much of a chemical life now, really.

Going back to being a bit more natural, being outside,

climbing trees.

We need to go a bit further back to that as we can

in this sort of modern world.

I hope that we can take what we've learned today

and hope to improve Joe's lifestyle in any way which we can,

and also the other families that are suffering in the same way too.

Look, we may be able to pull this off like that.

How about that?

Is there anything there?

Like our families, perhaps the best thing all of us

can do to improve our microbial health is simply reconnect

with those old friends that we evolved with.

That's your idea of big, is it, Emma?

This is Harry, the cocker spaniel.

Harry! This is brilliant.

He's helping his proud owners,

Graham Rook's grandchildren - Emma and Ollie -

to find bugs and beasties.

Wonderful. Thank you, Harry. That's a huge beast.

There's got to be a bug under there.

Oh, look, that little centipede.

We've got two millipedes and lots more woodlice.

And these little guys.

Digging in the dirt is admittedly more of a canine pastime,

but we could learn a thing or two from Harry.

Well, we just saw Harry, for reasons I am unable to understand,

digging holes.

You know, I mean, he's got to pick up all sorts of interesting organisms

from the environment there.

He's managed to get some gubbins onto the lens.

Studies suggest that reconnecting with bacteria in the natural world

is good for our health.

Ooh, you finding anything else?

We can't all have dogs, but there are other ways to re-engage with

green spaces, no matter how small they may be.

Well, first we need to know more about what the ideal

small green space would be, and what are the right plants

to have in it to encourage the right micro-organisms and so on.

Oh, look, there's a millipede.

It might mean then that to get the health benefit of green space,

you don't have to have places the size of Richmond Park here.

It might be possible to have much smaller green spaces

that are specifically designed to contain and release

into the environment the right micro-organism.

It'll come. You know, there are going to be ways ahead for all of this.

Come on, let's go for a walk.

Scientists may still be on the cusp of understanding precisely

which bacteria we need to reconnect with.

Hey, what sort of poo is that?

But Graham has no doubt about how important they are for our health.

There are still of course a few people left on planet Earth

who think of humans as some sort of plastic creature

that arrived from space, and was plonked onto a world

and is completely separate from that world, but of course we aren't.

We evolved within this biosphere.

We are a part of this biosphere,

and in a way this realisation that humans are in fact ecosystems

and that we depend so much on these micro-organisms is probably

the most important advance in medicine in the last hundred years.

I would regard it as more important in a way than

the solving of the genetic code.

For a start, most of our genes are not human anyway.

Come on, then!