Heyday of Hay Fever
In the north, autumn snows creeping down the mountains have long been known as "termination dust." That first white glitter signals the beginning of the end for summer jobs, building projects--and seasonal sneezes. Hay fever sufferers have real reason to welcome the first snows, and there are more of them every year: allergy to wind-borne pollen is an epidemic on the increase.
Surprisingly, it's a relatively new disease. The first accurate account of hay fever entered medical annals only in 1819,when a London physician described his own "unusual train of symptoms." The first American description of hay fever didn't appear until 1852. In Japan, it was virtually unknown before the 1950s.
There's always a suspicion that minor diseases appear or increase when people are less plagued by major illnesses (why worry about a seasonal runny nose when you're dying of tuberculosis?) and are more willing to report comparatively trivial symptoms to their doctors. Yet detailed historical studies show that the number of hay fever sufferers did increase rapidly during the 19th century, and clinical statistics suggest the increase is continuing.
This bloom of allergy doesn't make evolutionary sense. People and pollen have coexisted peacefully at least since protohominids went roaming semi-upright through clouds of grass pollen on the African savannas. Is something new in the environment triggering trouble?
Maybe so. In 1926, Swiss researchers surveyed the difference between city and country dwellers for hay fever occurrence. They found that people living in urban areas were ten times more likely to suffer from hay fever than were their country cousins, even though pollen densites were higher in the country. A 1985 Swiss study of 2500 people showed the country-city difference had disappeared.
The Swiss say a single factor explains both results: air pollution. In 1926, the cites had polluted air, but the country air was clean. By 1985, air pollution was pervasive.
Some Japanese research seems to corroborate the Swiss view. Cedar pollen is the chief cause of hay fever in Japan, but only five percent of the people living near cedar forests suffer from pollen allergy--unless they also live near busy roads. There more than 15 percent of the residents have hay fever symptoms.
Air pollution seems to make the perfect villain, except for one glitch in the historical record. It wasn't the urban poor, forced to breathe air fouled by uncontrolled factories, who suffered the sudden surge of hay fever symptoms in the last century. It was the upper classes, who often lived under clear skies far from the smoky source of their wealth.
Recent work in Britain now suggests that the aristocrats may have had problems because their upbringing, not their air, was too clean. Epidemiologist David Strachan thinks children are protected against hay fever if they have older brothers or sisters sneezing at them.
He bases his contention on the medical records of more than 17,000 children. What determined best whether a given child would develop hay fever was family size and birth order. Only children were far more likely to develop pollen allergy than were those with several siblings in the household; least likely victims were those with four or more older brothers and sisters.
Strachan suggests two mechanisms to explain his findings. A childhood viral infection possibly affects certain cells in the immune system, making them permanently less reactive--and it's certainly true that siblings pass diseases around despite parents' best efforts. More probable, perhaps, is that older children expose younger ones to small amounts of pollen by sneezing on them. Pollen already weakened by exposure to one nose before being passed by a sneeze to another might induce tolerance instead of an allergic reaction. There's at least circumstantial evidence that this mechanism might work: One treatment for hay fever is gradual desensitization, with initially tiny and slowly increasing doses of the offending pollen administered to the patient during the weeks before the natural pollen bloom occurs.
This speculation may bring comfort to harried parents and day-care center operators trying to contain sneezes, but it's little use to adult hay fever victims. With no way to rearrange birth order or family size in the past, they can only work for clean air in the present--and greet termination dust with pleasure and relief.
