But maybe it's not so simple. We live in a nation where states have enacted legislation permitting asthmatic children to carry their inhalers to school (one in 13 must do so). A federal labeling law mandates manufacturers clearly state in plain English whether major allergens—peanuts, soy, shellfish, eggs, wheat, milk, fish, and tree nuts—are ingredients in any product. And Americans spend billions of dollars annually on antihistamines to treat the symptoms of allergies.

Those of us over 40 don't remember having so much as a conversation about food allergies in school. Today 6 percent of young children have food allergies—and the number of those with potentially fatal peanut allergy doubled between 1997 and 2002. Children like Cameron sit at special tables at lunchtime; there are websites and support groups for parents homeschooling their severely allergic children.

Still, most allergies seem relatively innocuous. And it's true that more people believe they have allergies than actually do. For example, the gas and stomach pain of lactose intolerance? Not an allergy. But the rise in allergies is real. On a global level we need to better understand what's happening.

Here's how an allergy unfolds: One day, a body is exposed to a protein in something that seems perfectly harmless—the wheat flour, say, in a home-baked muffin. But for some unclear reason, the body looks at the protein and sees Trouble. There will be no symptoms at first, but the body is remembering—and planning.

That first exposure causes the immune system to produce an antibody called IgE (immunoglobulin E). Then IgE antibodies attach to certain cells, called mast cells, in tissue throughout the body. There they stay like wary sentinels waiting for war. With a second exposure, even months later, some of the allergen binds with the IgE on the mast cell. This time the mast cell releases a cascade of irritating chemicals: histamine, prostaglandins, and leuko trienes, which cause inflammation, work on nerve endings to make you itch, affect blood pressure and muscle contractions, and act on glands to cause mucus production and vasodilation, so you clog up.

A minor or isolated reaction can become chronic with repeated exposure to an allergen, or when other cells involved in the immune system, the T cells, come into play. Certain T cells remember the "insult" of the allergen and ensure that some part of the body keeps becoming inflamed. Often the allergen and the immune system become increasingly antagonistic, and the reaction worsens.

Sometimes, however (particularly with food allergies), the process is not gradual at all. This is what happened when Cameron Liflander ate tuna fish. He had to have been exposed to the allergen at least once before for IgE to be attached to mast cells and ready to react, but once the reaction was triggered by a subsequent exposure, an anaphylactic crisis occurred imme-diately. An allergist's tests showed that Cameron was severely allergic to fish, shellfish, mustard, sesame, peanuts, tree nuts, soy, dogs, cats, some antibiotics, mold, pollen, and dust mites. "The doctor said Cameron tested positive to more substances than almost any child he'd ever seen," Pamela Liflander says.