NEW YORK — Allergies are mysterious things, especially considering they affect more than 50 million people in the United States. We have a basic understanding of how allergies work - sufferers produce an antibody called Immunoglobulin E when exposed to substances that are otherwise harmless, like cat dander, peanuts, or ragweed. IgE sets off a chain reaction that results in sneezing, sniffling, and red, itchy eyes.
One of the biggest mysteries is why the disease comes and goes, and then comes and goes again. People tend to experience intense allergies between the ages of 5 and 16, then get a couple of decades off before the symptoms return in the 30s, only to diminish around retirement age.
Three types of explanations have been proposed: environmental, infectious and psychological. But as Mitchell Grayson, an associate professor of allergy and immunology at the Medical College of Wisconsin, points out, they're pretty speculative: "They're not quite hypotheses - there's not even enough evidence to call them that."
Most people live relatively stable lives between birth and 18 years of age. Whatever substances they develop allergic reactions to in their early years are likely to remain in their environment as long as they stay in their parents' home. Once they establish independent lives, though, they may get free of what was ailing them for so many years. College dormitories, while cesspools of infection, are relatively hypoallergenic compared to most homes. Tile floors, cheap, plastic-covered mattresses and the absence of dogs and cats may all contribute to the reduction in allergic symptoms.
A more technical explanation for the disappearance of allergies in the late teens involves viruses. When you infect a mouse with certain viruses, its immune system becomes extremely responsive to IgE. Although our immune systems don't work quite like the immune system of a mouse, there are some tantalizing hints that something similar could be at play in the human body. Infants that have been diagnosed with respiratory syncytial virus or even simple cold viruses go on to develop allergies at a significantly higher rate than kids who haven't suffered from these infections. This may also partially explain why most children develop pet allergies at a younger age than they do pollen allergies. Pets are present during cold season, and their dander could cause an immediate immune response while the virus is in the system. Pollen is less likely to be around at the same time as a virus.