ABSTRACT
The thicker scalp skin, with abundant pilosebaceous units and a relative absence of rhytids or crevices, is the ideal barrier against contact dermatitis. Even in cases where an aggressive allergen is present, the scalp is often not affected or only minimally affected, despite significant involvement of the face, ears and/or neck. It is often more useful to talk about “scalp-applied” irritants and allergens rather than isolated scalp contact dermatitis. Patients with documented scalp dermatitis who underwent patch testing showed that hair dyes, hair cleansing products, and medicaments combined for nearly two-thirds of the positive patch test reactions. The rinse-off or drip pattern sign is a clinically useful clue to suggest a scalp-applied allergen. An emerging allergen frequently applied to the scalp is Melaleuca alternifolia, commonly known as tea tree oil. Minoxidil may be the most frequent cause of scalp dermatitis medicamentosa.
