How getting your hands dirty in the garden perks up your immune system

ABIT of dirt never hurt any-one, right? That’s what we tell ourselves. Besides, isn’t our modern attach-ment to anti- bacterial everything supposed to be making us ill and leading to a rise in allergies?

It’s true we live in one of the most allergy-prone countries in the world. Cases of eczema and hay fever have trebled in the past three decades, while hospital admissions for anaphylaxis, the most severe form of allergic reaction, have increased six-fold, reports Allergy UK.

The reason, some suggest, is our enthusiasm for cleanliness. Our sterile homes and obsession with soap have disrupted our relationship with the bac-teria and parasites that evolved with us.

‘We’re too clean,’ a celebrity doctor announced recently, suggesting that children should stop washing their hands before meal-times.

But this is too simplistic. ‘There is good evidence to suggest that continued exposure to our microbial world is important for us,’ says Professor Sally Bloomfield, a microbiologist at the London School of Hygiene and Tropical Medicine.

‘But encouraging people not to wash their hands at a time when we’re being urged to avoid antibiotics, and when there are new germs around, is a very dangerous message to be putting out.’

So just how much dirt is good for you? Or rather, are you getting enough of the right sort of dirt?

The idea that cleanliness might make you more prone to allergy can be traced back to 1989, when Professor David Strachan, an epidemiologist now at St George’s hospital in Tooting, South Lon-don, put forward his ‘hygiene hypothesis’.

He’d been grappling with a paradox: although in Western countries the avail-ability of clean drinking water, childhood vaccinations and sanitation had reduced the incidence of diseases such as cholera, allergies were becoming more prevalent.

Professor Strachan discovered that children with fewer older siblings tended to be more prone to hay fever than those with lots of them. Perhaps, he said, children from large families were exposed to more childhood infections — and this protected them against allergies.

His theory was that if immune cells aren’t ‘trained’ by microbes via childhood illness during development, the balance of the cells is tipped, resulting in runaway inflammation and allergies (where the immune system overreacts to substances such as pet dander — tiny flecks of skin).

THe

hygiene hypothesis as formulated by Professor Strachan has since been ‘ reinterpreted’ to mean that our modern obsession with getting rid of ‘germs’ — by means of excessive cleaning — is making us ill because we’re not being exposed to microbes.

But there were problems with the hygiene hypothesis. For one thing, it’s not just allergies that are linked to fewer siblings; autoimmune diseases such as type 1 diabetes and multiple sclerosis are, too.

Indeed, studies have since contradicted the idea that infections are to blame anyway.

‘ You are not protected from allergic disorders by having child-hood virus infections, or by having older siblings who have childhood virus infections,’ says Graham Rook, emeritus professor of medical microbiology at University College London.

‘If anything, it makes it worse. If you have these viruses, they will trigger allergic problems.’

Possibly it’s not lack of exposure to viral infections that lies behind the rise in allergies, but insufficient exposure to bacteria and parasitic worms. In other words, the prob-lem could be that we’re not exposed enough to microbes from animals and in the great outdoors.

Children exposed to farming and cowsheds early in life seem to be protected against allergies and asthma, and especially if their mother is exposed during pregnancy.

In 2014, a paper in the Journal of Allergy and Clinical Immunology found that infants born into homes with cockroach droppings and dander from cats and mice had lower rates of wheezing at age three compared with those from more sterile homes.

Infants living in homes with a greater variety of bacteria were also less allergy prone.

In the early 2000s, Professor Rook coined a term for this tweaked hygiene theory, the ‘old friends hypothesis’.

Basically, as hunter-gatherers, our immune systems were exposed to many organisms in soil, water, air and animals: we evolved along-side these bugs and had to learn to tolerate them in order to survive.

Now that we are more cut off from these ‘ old friends’, our immune systems are developing sub- optimally and they are over-responding to the wrong things, resulting in inflammation.

Meanwhile, the immune cells that should keep this inflammation in check (known as regulatory T cells), aren’t doing so effectively — resulting in allergies, asthma and autoimmune disease.

In other words, it’s not so much improved hygiene as other changes to our lifestyles and environment that are behind the rise in allergies and other health problems. ‘ You want your immune system to have a large repertoire of harmless organisms that it has learned not to attack,’ says Rook.

These include all the common bacteria that inhabit the gut, as well as ones you’re likely to encoun-ter in the natural environment.

‘If you have this, then, because all lifeforms are ultimately built from the same building blocks, you are equipped to recognise almost any-thing that comes along and mount an appropriate immune response.’

The problem, then, is our lack of exposure to a diverse range of microbes.

Many of us live in cities and a recent paper published in the Proceedings of the National Acad-emy of Sciences suggested that city dwellers have less diverse microbes on their skin than people in rural areas, because those in towns and cities are not exposed to soil and animals so often.

The same study also suggested that reduced microbial biodiversity was linked to an increased risk of allergic disease.

We are also passing on fewer of our microbes to the next genera-tion; fewer women breastfeed and increasing numbers of babies are born by caesarean — two major routes by which our gut flora become established.

Some hospitals are now offering to take swabs of the mother’s vaginal fluid and rub it on the skin of caesarean-born babies. ‘It should do no harm — and it may be benefi-cial,’ says Professor Bloomfield.

KISSING

and cuddling babies, not to mention transferring bacteria to them by sharing cups and spoons, is another route.

In 2013, a study published in the magazine Pediatrics found that the children of women who sucked their baby’s dummy to clean it were less eczema-prone than those who received a sterile one.

However, ditching the disinfectant will do little to combat the problem, says Professor William Parker, who researches gut biology at Duke University in the U.S. ‘ even if we never used soap again, we can’t pick up the organisms that we’re missing because we don’t come into contact with them in our daily life. We’re no longer a bunch of farmers tending the land.’

He adds: ‘ Less hygiene is just going to mean more infectious dis-eases such as flu and the common cold that are going to make our immune systems more inflamed.’

Or as Professor Bloomfield puts it: ‘The most important thing we’ve learned in the past ten years is the microbial species we need are not the ones that cause infections.’

Instead, the key is what she describes as ‘targeted hygiene’.

‘You can be as tidy or dirty as you like in your day-to- day activities, but you should make sure you’re hygienically clean at the times and places that matter. If you’re preparing a chicken, once it’s safely in the pot then you should clean up, and disin-fect the surfaces it has touched.’ Hand-washing after the loo is a must, as is regularly disinfecting the toilet seat, flush, taps, bathroom towels and door handles ( she recom-mends doing this once a week). This is because bugs from chickens and faecal bacteria are likely to make you ill if swal-lowed in large quantities.

Similarly, regular hand-washing is advisable if you, or someone close to you, has a cold or other obvious illness. It’s also worth carrying alcohol hand gel as a precaution, for when you’re outside the home.

‘Most microbiologists may choose not to wash their hands in public lavatories after a pee as they believe their own urine is safer for them than using public soaps and towels,’ says Tim Spector, professor of epidemiology at King’s College London and lead investigator of the British Gut project.

Although we may not be able to restore our microbial populations to historic levels, there are other steps we can take to boost their diversity. encouraging your children to play in the natural world is one.

‘Our outdoor environment is teem-ing with microbes, most of which are harmless, on every surface,’ says Professor Bloomfield. ‘They are also airborne so we inhale them constantly while we are outdoors.’

A diet rich in wholegrains, fruits and vegetables is another way of boosting microbial diversity, as they contain compounds that encourage the growth and diversity of beneficial gut bacteria, says Pro-fessor Rook, who follows this advice himself. He also spends ‘ as much time outside as possible’.

even so, our microbes are still only a part of what keeps our immune system healthy. Chronic stress, vitamin D deficiency, lack of exercise and eating a poor diet also play an important role by increasing inflammation in our tissues.

‘All of us have this loss of biodiversity that puts us at greater risk of inflammatory disease,’ says Parker.

‘It means we really have to watch out for these other four factors, and guard against them.’