Outrage over soaring prices for EpiPen, a life-saving allergy treatment, has drawn renewed attention to the number of children suffering from allergies.
As more children grapple with these ailments, the reasons behind the spike are still being debated. Lots of money is at stake: The diagnosis and treatment of allergies is a nearly $26 billion market, according to data from Grandview Research.
Research from the U.S. Centers for Disease Control and Prevention shows that food allergies in children have increased approximately 50 percent between 1997 and 2011, now affecting 1 in 13 children in the United States. This translates to roughly two students in every classroom.
About 90 percent of allergic reactions come from these eight foods alone: Milk, eggs, peanuts, tree nuts, soy, wheat, fish and shellfish. In total, food allergies cause about 300,000 ambulatory-care visits a year, just among children under age 18.
With those numbers on the rise, a few theories are being explored, including one linked to Western society's obsession with fighting germs. The so-called hygiene hypothesis posits that a lack of exposure to infectious agents early in childhood can create a scenario where the immune system mistakes a food protein as an invading germ.
To be sure, the idea that excessive cleanliness triggers immune ailments is still being studied and debated. However, a sizable number of physicians believe the hygiene hypothesis has some merit, including the FDA, which is also delving into the issue.
"We are being too clean," Dr. Leigh Vinocur of the American College of Emergency Physicians told CNBC recently. "We're essentially creating allergies for ourselves."
Vinocur said if medicines such as antibiotics or acid-reducing stomach medication are overused, the gastrointestinal tract can be altered, creating more health-related problems.
"We've gotten rid of so many basic microbes that we are exposed to, that our immune systems are sitting idle, waiting to rev up for an attack," Vinocur said.
Yet another reason for the explosion in allergies may be environmental changes. Allergist Dr. Ujwala Kaza has seen this change first hand, noticing an influx in patients coming into her office.
Climatologists say 2000-2009 was the hottest decade on record, and that the average annual temperature in the United States could rise by 10 degrees in coming decades. The warmer climate may worsen respiratory allergies, as the growing season for plants becomes longer and thus increase pollen and allergen counts, some scientists argue.
Dr. R. Sharon Chinthrajah of the Sean N. Parker Center for Allergy and Asthma Research at Stanford University believes the cause of allergies will ultimately come down to a combination of many factors.
Chinthrajah told CNBC that cleanliness and changes in the environment are contributing factors, but she also noted that how genes are expressed — known by its scientific term called epigenetics — play roles.
For instance, the various factors a baby is exposed to in utero may have a big impact on its childhood. The doctor said researchers are continuing to study what foods mothers eat during pregnancy, at different times in the trimester cycle, to determine how that impacts the baby.
"We are all trying to actively understand a certain part of the puzzle when it comes to allergies," she said. "Understanding small pieces will help us eventually figure it out."