Phthalates predispose mice to allergies.

Shigeno T, M Katakuse, T Fujita, Y Mukoyama and H Watanabe. 2009. Phthalate ester-induced thymic stromal lymphopoietin mediates allergic dermatitis in mice. Immunology 128:e849-57.

Dibutyl phthalate (DBP) rubbed onto mouse skin changed the chemistry of the rodents' immune system and made them more prone to developing contact allergies, reports a new study published in the scientific journal Immunology.

This is the first study to show how DBP modifies the mouse immune system to predispose it to developing a type of allergy known as contact hypersensitivity. The results support prior studies that have found a connection between phthalates and allergies.

Allergies are an immune response to a substance that is not usually harmful. The response, however, is often damaging and uncomfortable. Contact hypersensitivity occurs when an individual becomes sensitized to a chemical and the skin becomes inflamed after touching the substance. The allergic reaction to poison ivy is the best known example of contact hypersensitivity.

Roughly 20 percent of Americans suffer from allergies. Rapid increases in the prevalence of allergies – especially among children in urban areas – suggest that environmental factors play a role in predisposing people to developing them.

Dibutyl phthalate (DBP) is an airborne environmental pollutant. It is a plasticizer found in many common household products, toys, cosmetics and health products. DBP is an endocrine disruptor associated with developmental, metabolic and reproductive disorders. It has also been shown to sensitize skin during immunological studies.

In this study, researchers sensitized mice to chemical mixtures by rubbing them onto the left ears. During the sensitization process, chemicals interact with proteins in the skin and are recognized as a foreign body or an antigen by the immune system.

Five days later, they rubbed the same mixtures on the mice’s right ears. They noticed that the mixture that contained DBP caused an allergic reaction. The mice ears became swollen after this second exposure. The mice rubbed with the mixtures without the chemical did not react.

After testing the individual components of the mixture, scientists discovered that DBP is the chemical that caused mice to elicit an immune response after the second exposure. The first time the DBP-containing substance was rubbed on a mouse's ear, it changed the protein chemistry of the immune system to make it react more severely to consequent exposures.

These findings suggest that exposure to environmental pollutants such as DBP can contribute significantly to developing allergies.