Pray for me, for I am planning a group camping trip. Two of our group cannot eat gluten. One can’t do dairy. One swells up when bitten by mosquitos, and half of us have hay fever. Were we always so allergic to our food and environment?

According to Dr Adam Fox, consultant paediatric allergist at Guy’s and St Thomas’ hospitals in London, UK, allergies and intolerances are “scientifically very clearly delineated”.

The word “allergy” stems from the Latin for “other response”. Typically, the immune system, Dr Fox explains, reacts to foreign substances in one of two ways: either it recognises them as benign (food, say) and ignores them, or identifies them as infectious agents (like bacteria, or viruses) and attacks them. Allergic reactions involve a third response.

Here, something that should be harmless, such as peanuts or pollen, provokes an immune response that harms you instead of protecting you. For severe food-related allergic reactions, the rise in admissions is even greater. This is because among the chemicals released is histamine, which can provoke a range of symptoms explains Dr Fox, from the irritating — “itchiness, sneezing, running nose,” — right through to the incredibly dangerous – “anaphylaxis, a severe, potentially life-threatening allergic reaction”.

An intolerance, however, is never this severe. Dr Fox explains that instead an intolerance is a reproducible reaction that doesn’t involve your immune system, but most commonly your gut.

Scourge of self-diagnosis

Whether you suspect an allergy or intolerance, do not be tempted to order a test online. The only reliable test involves excluding foods, then reintroducing them, to see if things get better then worse again.

When it comes to allergy tests however, Dr Fox says there are three reliable ones available. There’s the skin prick test — in which a doctor places a small amount of the allergen on the skin, then scratches it with a lancet and watches for redness and bumps, which indicate
an allergy. There’s a blood test, too, which measures the amount of allergic antibody (IgE) to particular proteins.
“A high level of allergic antibody to peanuts makes it more likely you have a peanut allergy. The higher the level,
the more likely the patient is allergic,” says Dr Fox.

Finally, when we genuinely aren’t sure, “the only thing we can do is expose the child to the thing and see that they react or not, under very careful conditions”. Whichever test is used, expertise is required to interpret the results.

Allergy epidemic

So are allergies actually on the rise? “Well, they’re certainly not new,” says Dr Fox. Britannicus, the son of Roman Emperor Claudius, was so allergic to horses he would break out in hives every time he rode. But their rise to prevalence began in the 20th century.

“In the 1860s, it took the doctor Henry Hyde Salter 15 years to collect 50 cases of asthma in London. Now, if you go into a school, just under one in three children are carrying an inhaler,” says Prof. Stephen Holgate at the University of Southampton, UK. Food allergies meanwhile appear to have mushroomed around the millennium.

Root cause

“Back in the 1980s a theory took hold called ‘the hygiene hypothesis’,” explains Dr Fox. “The gist was that we’re much cleaner than previous generations were, so our immune systems aren’t being challenged early and so are developing inappropriate allergic responses.”

What modern science believes to
be happening is slightly subtler. “It’s often referred to the ‘old friends hypothesis’, because it relates to the positive
relationship we have with bacteria that have colonised our guts over millennia, helping us develop appropriate immune responses,” explains Dr Fox.

Over the last 50 years, our gut flora have changed dramatically. And this has changed the way our immune systems develop their relationship with the outside world, tilting us towards more allergic responses. One major reason appears to be the distance from the animal kingdom in our modern times. Holgate cites two groups — the Amish and the Hutterites — who emigrated from the Tyrol in Austria to America sometime in the 18th century.

The Amish held on to their traditional agricultural practices and lifestyles, while the Hutterites adopted industrialised farming practices. A 2016 study found that, despite their similar genetic ancestries, allergies affected 7.2 per cent of Amish school children. Among Hutterite children, the prevalence stood at 33.3 per cent.

“In Amish communities, the animals are housed in sheds adjacent to the living space,” says Holgate. “It was the breathed and the swallowed environment, coming from the domestic animal stock, that was important. Go into a cow shed, there is that characteristic smell. That’s the microorganisms in the air, giving off chemicals. And it’s those microorganisms, which we’ve separated ourselves from,” he adds.

Across the world, when our connection with livestock drops, the diversity of gut and respiratory flora drops, and allergy rates “go whistling up,” points out Holgate.

Daily Telegraph