Dec. 3, 2012 — People exposed to higher levels of certain germ- and weed-killing chemicals may also be more likely to develop food allergies, a new study shows.

The chemicals are called dichlorophenols (DCPs). They are created by the breakdown of common pesticides, including chlorinated chemicals used to purify drinking water. They also turn up in moth balls, air fresheners, deodorizer cakes in urinals, and certain herbicides sprayed on crops.

“They’re quite common,” says researcher Elina Jerschow, MD, an allergist at Montefiore Medical Center in the Bronx, N.Y.

Doctors don’t know why, but rates of food allergies are rising in the U.S. A 2008 study by the CDC found an 18% jump from 1997 to 2007.

Jerschow wondered if increased protection from germs might somehow be lowering the body’s tolerance to foods.

Pesticides and Food Allergies

Using data collected by the National Health and Nutrition Examination Survey (NHANES), she compared levels of the chemicals in urine to antibodies to foods in the blood.

She admits that’s an imperfect way to measure food allergies, since people can be sensitive to certain foods without having any problems when they eat. Of the 2,211 people included in the study, most had detectable levels of DCPs in their urine. About 400 showed sensitivity to at least one food, like peanuts, eggs, or milk. More than 1,000 people were sensitive to an environmental allergen, like ragweed or pet dander.

People with the highest levels of of the chemicals were nearly twice as likely to show sensitivity to at least one food compared to those with lowest levels of those chemicals. That remained true even after researchers adjusted their data to account for other factors, like race, age, and a diagnosis of allergies or asthma.

“For some reason, in our study, we found people who were sensitized to foods had the highest levels of dichlorophenols,” Jerschow says.

The study is published in the Annals of Allergy, Asthma, and Immunology.

More Research Needed

The study doesn’t prove that DCPs cause food allergies. It merely shows the two are related in some way.

Still, the study lends some support to an idea called the hygiene hypothesis. The hygiene hypothesis suggests that the cleaner our environment, the sicker we become, since our immune system has been robbed of the opportunity to meet and fight off invaders.

Experts who were not involved in the research say the idea that pesticides may be a driver of food allergies is an interesting idea, but they aren’t yet convinced of the connection.

“The massive increase in food allergies is a relatively recent phenomenon, but we have been using chlorine to disinfect tap water since the mid-19th century. So it does not seem likely that the source of the problem is chlorinated tap water,” says Elizabeth Scott, PhD, co-director of the Center for Hygiene and Health in Home and Community at Simmons College in Boston.

But since drinking water isn’t the only source, it may be that we’ve reached a kind of environmental tipping point with these chemicals.

It’s an idea that needs more study, she says.