The list of allergens includes, but is not limited to, latex, gold, pollen, penicillin, insect venom, peanuts, papayas, jellyfish stings, perfume, eggs, the faeces of house mites, pecans, salmon, beef and nickel.
Hay fever brings sniffles and stinging eyes; allergies to food can cause vomiting and diarrhoea. For an unlucky minority, allergies can trigger a potentially fatal reaction known as anaphylactic shock.
EpiPens save lives, and antihistamines can often reduce symptoms; but these drugs also cause drowsiness. We might have more effective treatments if scientists understood allergies, but a maddening web of causes underlies allergic reactions. And there’s an even bigger mystery: why do we even get allergies at all?
“That is exactly the problem I love,” Ruslan Medzhitov, a professor of immunobiology at Yale, told me recently. “It’s very big, it’s very fundamental, and completely unknown.” Over the past 20 years, he has made groundbreaking discoveries about the immune system.
Now he is trying to find out how we get allergies. No one has a firm answer, but one theory suggests they are a misfiring of a defence against parasitic worms.
Professor Medzhitov thinks that’s wrong. Allergies are not simply a biological blunder but an essential defence against noxious chemicals – and one that has served our ancestors for tens of millions of years.