Is our drinking water making us sick?

Over the past 20 years, the number of people allergic to milk, eggs, wheat nuts and shellfish has soared, jumping by 18% between 1997 and 2007, according to the U.S. Centers for Disease Control and Prevention (CDC). But why?

A team of researchers reporting in the Annals of Allergy, Asthma and Immunology, the journal of the American College of Allergy, Asthma and Immunology (ACAAI), decided to look at whether that rise in food sensitivities could be related to another growing trend during that time period — the use of environmental pesticides and purifying chemicals.

(MORE: Why Kids with Known Food Allergies Are Still at Risk)

Specifically, the scientists focused on a group of pesticides called dichlorophenols that is also used to purify water. They began with 10,348 participants from the US National Health and Nutrition Examination Survey 2005-2006, 2,548 of whom showed dichlorophenols in their urine. In the end 2,211 were included in the study; food allergy was found in 411 of these participants and 1,016 had an allergy to an environmental agent, whether it was air pollutant or compounds found in products like pesticides. Those with higher levels of dichlorophenols in the body were 80% more likely to have food sensitivity than those with lower levels, and the authors believe the exposure to the chemicals may be contributing to a hyper-sensitive immune system that recognizes even common food proteins as foreign.