Why are we so allergic? Suddenly it seems that everyone is allergic to something, from pet dander to peanuts. Why is it happening and what can you do? - Exclusive Report

EVEN IF YOU DON'T HAVE ALLERGIES, chances are that a family member or co-worker does. Studies and anecdotal reports show that the number of adults and children with allergies is growing rapidly.

Researchers confirm the surge, though definitive statistics are hard to come by. "It's clear that allergies have increased, and it's a major problem," says Andrew Liu, M.D., an allergy researcher at the National Jewish Medical and Research Center in Denver. A 1999 survey by the American College of Allergy, Asthma and Immunology (ACAAI) in Chicago found that 38 percent of the 1,000 adults polled had allergies like hay fever--almost double the number researchers expected to find.

School nurses have also noticed the trend. When Karen Kaverman, R.N., began to work at the private Breck School in Minneapolis 10 years ago, only three children had identified food allergies. Now more than 20 out of 1,200 do. "We also have lots of kids with environmental allergies, and when I started I didn't see as much of that either," she says.

Allergies signal an immune system in trouble. If you have a respiratory, food, or skin allergy, your immune system launches a sudden all-out attack on a harmless substance like pollen, animal dander, peanuts, or latex. Because your immune system misreads this substance as a dangerous invader, it immediately releases inflammatory chemicals to flush it out, triggering symptoms ranging from sneezing to the potentially deadly anaphylaxic shock. (Food allergies differ from food intolerances and sensitivities, which may produce allergy-like symptoms but involve other mechanisms in your body.) You can develop allergies at any point in your life, researchers say.

And they create more trouble than immediately meets the eye. In a recent survey by the ACAAI, 94 percent of sufferers reported that their allergies took a toll on everything from work to sleep to sex. Allergies also increase your risk of asthma and may even harm your heart: Two studies found that IgE, an antibody your body produces during allergic reactions, is associated with increased heart attack risk.

Although your genes definitely play a role in whether or not you get allergies, many experts believe that something has changed in the way we live to spark what they say is an epidemic. There are several possible explanations; in this report we detail the four most popular theories. Fortunately, you can take measures to prevent allergies; we'll show you how. And if you or any of your family already have allergies, we provide simple, natural ways to treat them.

Cleanliness May Be to Blame To explain why we're so allergic, some researchers have proposed a theory called the hygiene hypothesis, which suggests that you need exposure to germs as a child to develop a properly functioning immune system. Some researchers think that adults, although their immune systems are already developed, might also benefit from exposure to certain germs.

To understand this theory, imagine an 18-month-old digging in the dirt. While digging, he's naturally exposed to microbial compounds. Researchers are particularly interested in one of those compounds, known as endotoxin, which is the remains of dead bacteria and too small to be seen with a microscope. Some researchers wonder if the child's developing immune system reacts to endotoxin and possibly other microbes in the dirt by shutting off the aggressive immune responses that lead to allergies.

Now imagine that the family dog comes over and licks the boy's face. This gives his immune cells still more stimulation; endotoxin is particularly abundant around animals. A study in the Journal of the American Medical Association last August found that children exposed to two or more pets in their first year were half as likely to have allergies (to dust mites, ragweed, grass, dogs, and cats) at ages 6 and 7 than children without pets. Scientists speculate that to be effective, this exposure to pets and dirt may need to happen daily, from soon after birth until a child is 2 or 3.

But this scenario isn't happening enough, say proponents of the hygiene hypothesis. Much of the problem is beyond our control; experts believe that environmental bacteria and endotoxin exist in much lower concentrations than they did in earlier times, when people were more likely to encounter germs in mud and untreated water. But we're also obsessively clean, showering once or more every day and spraying, dusting, and scrubbing Our homes to spotlessness. We're especially clean around our babies, whose immune systems are in their most critical development phase, says Fernando Martinez, M.D., professor of pediatrics and director of the Respiratory Center at the University of Arizona in Tucson.

While experts don't suggest that we quit keeping our kids clean (after all, hygiene prevents deadly diseases), some say relaxing our standards might not be all bad. "You wouldn't want to lick the inside of a raw chicken, but there's not the slightest reason why your child shouldn't play in the garden and come back and have his hands covered in earth and eat a [snack]," says Graham Rook, professor of medical microbiology at University College London in England. In fact, some studies show that allergies of all types are less common in children who wash their hands less frequently.