According to the Centers for Disease Control and Prevention (CDC), 4 to 6 percent of children in the U.S. suffer from a food allergy and the number has increased 18 percent from 1997 to 2007.

The most common food allergies are milk, eggs, fish, crustacean shellfish, wheat, soy, peanuts and tree nuts, which account for 90 percent of all food allergies. While not all food allergies can cause anaphylaxis, a sudden reaction that can be fatal, children with food allergies are two to four times more likely to suffer from asthma or other allergic issues.

The CDC also published a major study on children and allergies several years ago. The results were astounding. Among other things, the government survey suggested:

  • 1 in 20 children have food allergies (up 50 percent from the 1990s)
  • 1 in 8 have skin allergies or eczema (that number is up 69 percent)
  • There has been no increase in hay fever or other respiratory allergies

One of the most common food allergies, peanuts, is increasing at an alarming rate. Researchers from the Jaffe Food Allergy Institute in New York discovered that the number of children who are allergic to peanuts increased from one in 250 children in 1997 to one in 70 in 2008.

"It really is almost an epidemic," Dr. Scott Sicherer, the institute's director, told CNBC. "It's impossible to deny an increase, even with anecdotal reports from school nurses," he said, adding that "about two (children) per classroom have food allergies. It's not just our imagination."

In some ways, these numbers are no surprise.

The hygiene hypothesis

Hand washing and hygiene Does this research mean we should stop washing our hands? It's not a simple yes-or-no answer. (Photo: Oksana Kuzmina/Shutterstock)

Experts do tend to agree, however, that instances of both food allergies and hereditary atopic disorders such as eczema and asthma have seen a dramatic increase in recent decades, at least in so called "developed" economies. And herein may lie a big clue: Westerners may be experiencing more allergies because our culture has become too effective at controlling or eliminating exposure to microbes.

Microbes, you see, are central to training our immune system to deal with allergens.

Nevertheless, researchers like SF Bloomfield of the London School of Hygiene and Tropical Medicine in London warn against too simplistic a reading of this so called "hygiene hypothesis." If your child develops allergies, it's not necessarily because you cleaned your house too well. It's more likely the result of broader, societal changes.

Rural kids have fewer allergies

Studies would seem to back up this broader, societal reading of the "hygiene hypothesis."

Kids are less likely to develop asthma if they grow up on farms, for example. And children in cities have more food allergies than those in the country. (Exposure to air pollution in cities may also be a factor in this latter case.) There have even been studies suggesting that babies born in hospitals, and particularly those born by cesarean section, may have a different balance of gut bacteria making them more prone to allergies.

Food guidelines revised

Finally, it's worth noting recommendations as to how and when to introduce potential food allergens to a child's diet.

As my wife Jenni, a registered dietitian, said it used to be recommended that parents avoid giving children cow's milk until the age of 1, and tree nuts before the age of 2. In 2008, the American Academy of Pediatrics revised its guidelines, stating that unless there was a strong family history of allergies, potential allergens could be introduced as and when developmentally appropriate. (Parents should still avoid whole nuts and thick layers of peanut butter with young children as they are a potential choking hazard.)

Mostly, it appears that these guidelines were revised because there was simply no correlation between the onset of allergies and the withholding of certain allergens. Yet some researchers like Morton Galina, a pediatric allergist at Atlanta's Emory School of Medicine, have even suggested that there may be more going on — and that the previous practice of not giving children allergens may in fact have increased, not decreased, their risk factor.

Emory's Galina said the new CDC statistics may reflect a recent "sea change" in the recommendations for when young children should first eat certain foods. In families with a history of eczema or food allergies, parents were advised to wait for years before introducing their young children to foods tied to severe allergies, like peanuts, milks and eggs. But professional associations changed that advice a few years ago after research suggested that allergies were more likely in those kids when the foods were delayed.
The old advice "was exactly the wrong thing to do," and could have contributed to some of the increased cases, Galina said.
As with most things in life, it seems the best advice is to practice moderation. Let your children play in the dirt, and then call them inside to wash their hands. Go ahead and feed them a PB&J sandwich; just make sure they are old enough to chew it properly.

Editor's note: This article has been updated since it was originally published in September 2013.

Why are so many kids allergic?
Sometimes it seems like every other kid is allergic to something. Is that really the case and, if so, what can be done about it?