Abstract
Background
Allergic contact dermatitis is an inflammatory condition that less commonly presents with scalp involvement. Recently, T regulatory cells have been documented to be residents of hair follicles, illuminating why contact allergens are less likely to elicit dermatitis in the scalp.
Objective
The aims of the study were to determine the prevalence of scalp symptoms, with and without other affected areas, in patients presenting for evaluation of allergic contact dermatitis and to determine the allergens most likely to be associated with scalp dermatitis.
Methods
We examined allergens commonly found in hair products and stratified positive patch test results by the following affected areas: face, eyelid, neck, or hands, where exposure by runoff is common, versus scalp.
Conclusions
Para-phenylenediamine (PPD) is the most common allergen in patients with scalp dermatitis. The rate of PPD sensitization is higher in nonwhite compared with white patients. In the small number of patients with isolated scalp involvement, positive patch tests to PPD were documented in a minority. Other allergens found in hair products may present without scalp symptoms. Patients with dermatitis affecting areas other than the scalp should provide their hair product ingredients to guide patch test selection.
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