Why is food allergy increasing? Skin might be involved

Food allergy occurs in one of every 13 children in the U.S., nearly 6 million, and the incidence is increasing. Why this is happening has been a burning question for the public and researchers alike.

The "hygiene hypothesis," which has been proposed to explain the increase of allergies, holds that early exposure to germs impacts the immune system and lowers the risk of allergic disease. However, results published in Allergy and Asthma Proceedings showed that food allergy had less profound associations with hygiene factors -- such as pet exposure -- than asthma. While it is well established in asthma, the hygiene hypothesis has not been thoroughly investigated in food allergy.

"Our results do support the hygiene hypothesis showing that increased number of siblings is protective for food allergy," said lead author Ruchi Gupta, MD, MPH, pediatrician and researcher at Ann & Robert H. Lurie Children's Hospital of Chicago and Associate Professor of Pediatrics and Medicine at Northwestern University Feinberg School of Medicine. "The association of food allergy with early skin infection and eczema, however, might shed some light on how food allergies develop. Our findings support the hypothesis that food sensitization might start with exposure through the skin. This might have implications for prevention of food allergies."

The study included 1,359 participants, from birth to 21 years old, with and without food allergies. A unique strength of this family-based study is that it included siblings who may or may not have had allergies. The similar genetic makeup of the subjects and controls helped the authors assess the impact of different exposures on food allergy and asthma.

The study investigated key hygiene factors in association with food allergy and asthma, including antibiotic use, infection history, number of siblings, pet exposure, and maternal child health factors such as maternal age at birth, cesarian section, breastfeeding and out-of-home child care. The number of siblings and child care in a child care center were the only hygiene factors that were associated with decreased food allergy.