The hygiene hypothesis versus the skin theory

The hygiene hypothesis is a hypothesis that states a lack of early childhood exposure to germs increases the likelihood of developing asthma and allergies by suppressing the natural development of the immune system. However, some studies show food allergy has less profound associations with hygiene factors – such as pet exposure – than asthma.

Some of the more recent research is now focusing on the role of early exposure to food allergens through broken skin as the inception of food allergy development. For example, a recent study found increased prevalence of food allergy if a child had skin infections or eczema in the first year of life.

The study was conducted at the Ann & Robert H. Lurie Children’s Hospital of Chicago and included 1,359 participants, from birth to 21 years old, with and without food allergies, as well as siblings who may or may not have had allergies.

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, caesarian section, breastfeeding and out–of–home child care.

While the results do support the hygiene hypothesis – showing that increased number of siblings is protective for food allergy – the association of food allergy with early skin infection and eczema also supports the hypothesis that food sensitization might start with exposure through the skin.

A greater number of siblings were associated with a 21% decrease in the prevalence of food allergy and an 18% decrease in the incidence of asthma. Owning a cat was associated with 36% decreased prevalence of asthma.

The number of siblings and child care in a child care center were the only hygiene factors that were associated with decreased food allergy.

Reference: Gupta, et al. 2016. Allergy and Asthma Proceedings, Vol. 37(6) pp. e140-e146(7)

For additional reporting, see the Lurie Children’s Hospital website.