Shampoos.

Shampoos are used almost universally in developed countries to wash the hair on a daily basis. A number of known contact allergens are used as ingredients in shampoos, and contact allergy due to shampoos is a well known entity. Patch testing can be used to identify ingredients to which patients are allergic, after which the physician can help the patient to find a shampoo that is free of the ingredients to which they are allergic. The ingredients used in shampoos have not been systematically reviewed in recent years in the United States. We use a database of products sold at a major drug store to quantify the most frequent allergens used in shampoos. The allergens most commonly present, in order of prevalence are as follows: fragrance, cocamidopropyl betaine, methylchloroisothiazolinone/methylisothiazolinone, formaldehyde releasers, propylene glycol, vitamin E, parabens, benzophenones, iodopropynyl butylcarbamate, and methyldibromoglutaronitrile/phenoxyethanol.