Our allergies, ourselves

ONE HUNDRED YEARS AGO, an Austrian doctor named Clemens von Pirquet coined the term "allergy" to describe how the human body, once exposed to a foreign substance, could inexplicably develop a heightened, occasionally fatal, sensitivity to it.

At the time, according to "Allergy: The History of a Modern Malady," a forthcoming book by the University of Exeter historian of medicine Mark Jackson, such disorders were understood to be uncommon. Hay fever and asthma, for example, were diagnosed primarily among the leisured rich. Like tuberculosis and gout, allergies connoted intellect, sensitivity, even good breeding: The prevailing medical wisdom was that such disorders preyed only upon those with refined constitutions and sheltered lifestyles. Proust and Dickens, famously, were asthmatics. American hay fever sufferers formed associations and spent the late summers sequestered together in exclusive resorts in the White Mountains. According to Morell Mackenzie, a leading late-19th-century English physician, hay fever was "almost exclusively confined to persons of cultivation."

Today, of course, and especially this time of year, allergies carry no cachet. The American Academy of Allergy, Asthma & Immunology estimates that 40 million to 50 million Americans suffer from allergies; 35.9 million of those, the organization claims, have hay fever. An estimated 10 million suffer from allergic asthma. Food allergies account for 30,000 emergency room visits and 200 deaths a year.

If history is any guide, these numbers will rise. Jackson refers to several studies that showed a doubling in asthma, hay fever, allergic dermatitis, and drug allergies in Western Europe between the 1960s and 1980s, and similar trends have been observed in the US. A study published a year ago in the British Medical Journal, looking at telltale antibody levels, found a steadily rising sensitivity to 11 common allergens over the past three decades.

The term itself, meanwhile, has come to encompass more than the merely medical. We talk about how we are allergic not only to bee stings or penicillin, but, figuratively, to our jobs or our in-laws or to smooth jazz. "I used to wake up at 4 a.m. and start sneezing, sometimes for five hours," James Thurber is said to have complained. "I tried to find out what sort of allergy I had, but finally came to the conclusion that it must be an allergy to consciousness."

For all its ubiquity, though, allergy remains a puzzle. The allergic reaction itself is fairly well understood: An antibody called immunoglobulin E mistakes a harmless foreign substance (pet dander, say, or a peanut) for a dangerous invader, and triggers the runny nose, tears, itching, and swelling familiar to allergy sufferers. Yet there's surprisingly little agreement on what triggers that malfunctioning response, and why it seems to be happening so much more than it used to.

Over the years, the explanations (and there has been no shortage of them) have tended to break down roughly into two groups: those that focus on the proliferation of new substances we eat and inhale, and those that focus on the unintended effects of our cosseted, health-conscious lifestyle. In a sense, both sets explain allergies as what Jackson calls "a disease of civilization," the reaction of the human body to an increasingly manmade world. And which aspects of that world are to blame can depend as much on your view of society as on science.

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Allergies were already being blamed on modern living decades before von Pirquet coined the term. The American physician George Beard wrote in 1876 that hay fever was "essentially a neurosis" generated by the shocks of modern life. Among other things, writes Jackson, Beard blamed "novel modes of transport and communication; the range of 'unrhythmical, unmelodious' noises accompanying modern industrialization; an increase in the amount of business and the pace of discovery{hellip}domestic and financial troubles; the increased education and mental activity of women; and even greater liberty."

Beard's ideas were contested even in his day, and they didn't survive the 19th century. But as the medical understanding of allergy improved, the idea that allergies were a price to be paid for human enterprise didn't go away. In a recent essay, Gregg Mitman, a University of Wisconsin historian of medicine (his own book on the history of allergy is due out next year), quotes a hay fever specialist named Roger Wodehouse who worried in 1939 that increases in hay fever cases were "nature's reply to man's destructive and wasteful exploitation of natural resources." As Wodehouse saw it, overfarming had rendered much of the Midwest unfit for anything but ragweed (ragweed pollen was by then understood to trigger the allergy).

In the decades after World War II, an American allergist named Theron Randolph identified a different culprit. Researchers in England and the United States were by then noticing that hay fever rates continued to rise even in places where ragweed pollen levels--thanks to increased urbanization and changing agricultural practices--were declining. For Randolph the answer was clear: Rising hay fever rates, and allergy rates in general, were due to the increasing concentration of synthetic chemicals in our environment--smokestack emissions, car exhaust, household cleaning products, cosmetics, fertilizers, food additives, among many others.

Today Randolph's legacy (he died in 1995) is a controversial one, and the field he founded, clinical ecology, is associated with disputed disorders like multiple chemical sensitivity and Gulf War syndrome, whose physiological basis remains elusive. According to Daniel Hamilos, an allergist at Harvard Medical School, studies that have sought to find a link between allergy and pollution have yielded conflicting results. "Sometimes, in more polluted areas, especially in underdeveloped countries, you find fewer allergies." Nonetheless, Hamilos and others do believe that pollution plays some role in triggering and exacerbating allergies. Several studies have shown that diesel exhaust in particular does increase allergy rates, both in mice and humans.

As a result, allergy has been taken up by environmentalists, who have revived Roger Wodehouse's description of it as "nature's reply"--a sign of the dangers posed by our heedless mistreatment of the environment. Antipollution campaigns regularly mention rising allergy rates, and Greenpeace and European Green parties base their opposition to genetically modified food in part on the criticism that they might trigger food allergies. Environmentalist groups like the National Resources Defense Council have seized on research showing that both the increasing levels of atmospheric carbon dioxide and rising temperatures associated with global warming may increase the amount of pollen that ragweed and other plants produce.

Environmentalist critiques often take on a social justice element, as well. A 1999 study by Diane McLean of the Children's Health Fund found that 38 percent of New York City's homeless children had asthma, several times the overall national rate. Small urban environmental organizations like West Harlem Environmental Action and Boston-based Alternatives for Community & Environment were started in part to publicize inner-city asthma, which has ballooned in recent decades (60 percent to 70 percent of asthma cases are triggered by allergies).

Penn Loh, executive director of Alternatives for Community & Environments, describes asthma as a disease of poverty. "One of the biggest triggering factors indoors is mold, which is much more prevalent in older, rundown housing." And poorer neighborhoods tend to be hot spots for outdoor pollution, too, since that's where bus depots, truck garages, and the like are often found.

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Allergies, it seems, make for an all-purpose marker for societal ills. Even our growing girths have been implicated. The exact nature of the connection is up for debate, but, according to Javed Sheikh, the clinical director of allergy at Beth Israel Hospital, "obesity and asthma clearly seem to be linked."

Still, while the rise of allergies may indeed be the product of pollution, poverty, and sloth, it might also have very little to do with any of these. Slimmer Americans breathing cleaner air might still have reason to dread the spring.

One of the more widely accepted explanations for the rise in allergies is something called the "hygiene hypothesis." By killing off so many of the microbes and parasites that used to prey on us, the hypothesis suggests, we've thrown our immune system off balance. "We've more or less taken away an important function of the immune system," says Hamilos. "It tends to look for other things to do, and it looks to things that aren't very productive, namely attacking allergens."

Instead of focusing the blame on damage we've done to the environment, the hygiene hypothesis sees allergies more as an unintended consequence of our fight against more debilitating diseases. "We want to live longer and better," says Andrew Saxon, a leading allergy researcher at UCLA Medical School, "and the price is allergy."

As proof, researchers point out that allergy rates in poor countries--where diseases long since eradicated in the developed world still run rampant--are correspondingly lower, even in polluted urban centers. Some, like Sheikh, emphasize the role of a compound called endotoxin, produced by E. coli and other bacteria common in animal feces. Studies have found that children who grow up on farms (around microbial havens like untreated ground water, dirt, and manure) are less likely than their urban counterparts to develop allergies. Others look to intestinal worms, citing studies that show an increase in allergy rates among children given deworming medication.

In a related vein, some research has suggested that early exposure to an allergenic substance may actually protect one from developing allergies. As-yet-unpublished results from a study led by Gideon Lack, an allergist at London's St. Thomas' Hospital, suggest that, in countries where babies have a peanut-heavy diet, peanut allergy rates are a fraction of those in countries like England and the US where babies are not fed peanuts--out of a fear they'll prove fatally allergic. To see whether peanut exposure is actually decisive, in July Lack will begin a seven-year study, funded by the National Institutes of Health, in which hundreds of English infants will (under medical supervision) be fed peanuts on a regular basis, tracked to see what sort of allergies they develop, and compared with a peanut-free control group.

Similarly, work by Dennis Ownby, head of Allergy and Immunology at the Medical College of Georgia, has shown that being born into a home with multiple pets decreases dramatically one's odds of developing allergies of any sort.

As of yet, no doctor is suggesting that parents put their babies on a peanut diet or have them play in manure. But there have been attempts to figure out how to recreate certain antiallergenic aspects of the pre-modern lifestyle, what Sheikh calls "the particular dirty profile that leads to protection against allergy." Joel Weinstock, for example, head of Tufts New England Medical Center's gastroenterology division, has speculated that one possible cure for allergies might be a dose of a relatively benign parasite called the pig whipworm.

In the meantime, allergies will remain, as George Beard believed more than a hundred years ago, a disease of modern living--a disease of poverty, pollution, development, and cleanliness. In other words, an epidemiological Rorschach.

Drake Bennett is the staff writer for Ideas. E-mail drbennett@globe.com.