Will's Thoughtstream

Identifying what's responsible for the increased prevalence of allergies is difficult--but several theories abound. One is the so-called "hygiene hypothesis," which posits that we've done such a good job eradicating diseases and sanitizing our environment that our immune systems are looking for something to do. Another theory is that we're introducing potentially allergenic foods too early, or too late, into young children's diets.

Could it be that we're all exposed to more and more of the "Big Eight" allergens through processed foods and this might be contributing to the rising rates? "Possibly," says Annie Khuntia, M.D., clinical associate of allergy and immunology at the University of Chicago. "But it's really difficult to come to this conclusion because there isn't any evidence to support it. This issue hasn't been studied." At this point, say experts, most hypotheses tend to be, well, educated guesses. "Even the big players tend to disagree," says Khuntia. "It's an evolving science."

From UK Independent:

One of the most extraordinary increases has been in peanut allergy, up 117 per cent between 2001 and 2005. An estimated 25,000 people in England are affected, and many are at risk of a severe reaction if they are exposed to the nuts. The report says up to 7 per cent of infants have a food allergy - many are sensitive to egg, but this tends to improve with age. Among adults, the Institute for Food Research estimates that up to 2 per cent are affected. This is often distinguished from food intolerance which is less specific and thought to be more widespread.

The report says that guidance to pregnant women and children not to eat peanuts should be withdrawn because it may actually be exacerbating the problem of peanut allergy. In parts of Africa, where peanuts are made into a soup used for weaning and in Israel where they are incorporated into a rusk for babies, the problem of peanut allergy does not exist. Depriving children of exposure to peanuts early in life might increase the risk of an allergic reac tion later.

No one really knows [why allergies are on the increase]. Allergy is an area of medicine more full of puzzles than most. Take hay fever. In 1955, just over five GP consultations in 1,000 were for hay fever. By 1971, the number had doubled and a decade later it had doubled again. Yet this increase was occurring as pollen counts were falling owing to the cut back in agricultural land.

[The hygiene hypothesis] is the leading theory to explain the rise, devised by David Strachan in the 1980s. It can be summed up in a sentence: as we lead cleaner, germ-free lives, and are exposed to fewer illnesses in childhood because of smaller families, our immune systems are under-developed and over-react when exposed to allergens such as grass pollen, house dust mites and cat hairs. The theory has been confirmed by many studies since. Children raised on farms with livestock have a third fewer allergies than those who are not.

However, the theory does not account for the extraordinary increases in allergies such as asthma seen in townships in Tanzania, on Tristan Da Cunha (the tiny island in the south Atlantic) and other parts of the world remote from the infrastructure of developed nations.