If you have spent any time inside an elementary school classroom over the past few years, you have likely noticed signs banning peanuts or other types of food. The bans, which can apply to individual classrooms or entire school systems, are relatively new, especially in their widespread use. Teachers, aides, and other administrators are now frequently trained in the use of EpiPens, an auto-injector that can deliver a life-saving dose of epinephrine to a child.

The reason for all the precaution: the dramatic rise in food allergies among children over the past two decades. The exact numbers are up for debate, but the general trend is not. A study of 40,000 families conducted by Dr. Ruchi Gupta from Children's Memorial Hospital and an associate professor of pediatrics at Northwestern University's School of Medicine found that eight percent of kids had a food allergy. Another found that almost 15 million children were allergic to cow's milk, egg, soy, wheat, peanuts, tree nuts, shellfish, or fish.

Dr. Scott H. Sicherer, a professor of pediatrics and chief of the Division of Allergy and Immunology at The Mount Sinai Medical Center's Jaffe Food Allergy Institute, told me that his team conducted a random calling in 1997. It showed one in 250 children were allergic to peanuts. When they did the same study in 2008, the number jumped to one in 70. "That sounds crazy, because it's a tripling, but the numbers from other countries are similar," the American Academy of Allergy, Asthma & Immunology (AAAAI) fellow said, pointing to similar studies with similar results from Canada, the U.K., and Australia. (Hay fever, asthma, and eczema are also on the rise.)

The rise of allergy is likely due to a number of factors that are mostly the result of an increasingly wealthy, sophisticated, modern Western society. In other words, First World Problems.

Is the rise due to increased awareness about allergies or an actual rise in the percentage of people developing allergies? Allergists in the field generally agree that it's a little bit of the former but more of the latter. "We are convinced that there has been a true increase above and beyond better recognition," Dr. Robert Wood, who works at the Johns Hopkins University School of Medicine and is a colleague of Sicherer's at the AAAAI, told me. Dr. Kevin McGrath, an allergist and fellow of the American College of Allergy, Asthma and Immunology, agrees: "People are more aware of it so it's getting diagnosed more, but I think there's also a real increase." Anecdotally, those observations bear out as well. The country, hopefully, would have noticed if school children kept falling into anaphylactic shock 25 years ago.

PEOPLE DEVELOP ALLERGIES BASED on both genetics and environment. Sicherer and his team ran a study of peanut allergies on identical and fraternal twins. While only seven percent of fraternal twins had the same allergy, in identical twins—kids with the same genes—the rate of allergy was two-thirds. "That tells you two things,” he said. “One is that there's a strong genetic component. But on the other hand, one-third of the identical twins didn't share the allergy. So environment has a lot to do with it. And for the rate of allergies to increase over a 20-year period, clearly there is some environmental thing going on because genes don't change that quickly.

Environmental factors include a wide variety of things. For example, scientists have found that a child who grows up on a farm or lives in a family with at least one other sibling is less likely to develop allergies. (Interestingly, if they do, however, they are more likely to get asthma as well.)

These facts and observations lead, meanderingly, to one of the leading theories about the rise of allergies. The so-called Hygiene Theory states that changes in our environment—things like cleaner water, fewer parasites, and the use of antibiotics—have resulted in changes in the body, specifically the immune system. An allergy is nothing more than the immune system's response against proteins in the body and the environment. According to the Hygiene Theory, the immune system can't find anything harmful to attack, so it mistakes harmless food protein (or pollen, cat dander, etc.) for something invasive that needs to be remedied.

The Hygiene Theory has many advocates, and it's likely part of the picture, but it's not the entire explanation. "It's the leading theory, but that doesn't mean it's going to turn out to be the right one," Wood said. "It has some evidence to support it, but it's pretty clear to most of us that there must be other things going on. The world hasn't changed that dramatically in that short a time. We're talking about a 20-year timeframe. If we were talking about 100 years, you might be able to explain it, but the environment hasn't changed that much in 20 years."

Another theory posits that humans lack vitamin D because we spend more time indoors and then use more sunscreen when we are outside. Vitamin D deficiency has jumped in the past 15 or 20 years, and there's a noticeable increase in allergies reported in northern climates compared to the percentage reported in the south, where people are generally outside more.

A third working theory is that babies get too much folate. Roughly two decades ago, pregnant women began supplementing their diets with high levels of folic acid, which was shown to protect against spinal cord defects. This is obviously a good thing, but it may have contributed to the rise in allergies, although no one knows exactly why.

(One discounted theory: genetically modified foods. "Those theories haven't held up and don't look like they are part of this,” Wood said, “but they are big changes in our lifestyles over the past 20 years and they could still tie in.")

THE RISE OF ALLERGY is likely due to a number of factors that are mostly the result of an increasingly wealthy, sophisticated, modern Western society. In other words, First World Problems. "For any combination of these reasons, you don't see allergy in very under-developed countries,” Wood said. “We think the hygiene theory explains most of that. If a newborn baby is really exposed to really bad conditions and contaminated water and parasites, their immune system will not be spending any time worrying about allergy."

A good tradeoff? Probably. "[The allergies are] easier to take care of and treat than polio or rubella," according to McGrath.

The issue now facing these three doctors and their colleagues is two-fold: treatment versus cure. For now, and for the foreseeable future, treatment is the option. That means avoiding foods that cause an allergic reaction, keeping an EpiPen nearby, and raising awareness. Mistakes happen, but the risk to a person's life can be minimal. Hence the increase of peanut bans and other tactics. But still, "it's sort of like living in a field of landmines," Sicherer said.

Some good work is being done in the desensitization field. People who eat small doses of peanut flour in controlled situations and then continue eating a certain amount of peanuts per day can develop protection, although studies show that 10 percent of people reactivate their allergies. Additionally, a group of doctors in Boston has found some positive results using Chinese herbal medicine, and there is hope that this will yield some breakthroughs. Another thought is to try to stop the allergies from starting. Experts now recommend mothers expose their children to peanuts and other potential allergy-causing foods at an early age, a sharp change from the theories of the past.

But still, while these methods are effective, they are just treatments, not cures. (Think of an asthma inhaler, which deals with symptoms but does nothing to fix the underlying concern.) And the rise will continue. While the rate of asthma and hay fever has leveled off, food allergies will continue to accelerate over at least the next 10 or 15 years. Cures are a long way off. "I'll probably work for another 15 years or so,” Wood said, “and in that timeframe I don't see any hope that we'll have real prevention."

For now, expect to see more signs in classrooms around the country.