This summary discusses adult patients. Allergic contact dermatitis in children is addressed separately.

Contact dermatitis of the nail unit may be either irritant or allergic, and allergic contact dermatitis comprises 20% of contact dermatitis cases of the nail. Allergic contact dermatitis of the nail apparatus commonly involves the proximal nail fold (PNF) and the hyponychium and may cause both skin changes and nail plate abnormalities. Onycholysis is the most common nail change. Other nail findings include pitting, Beau lines, and onychodystrophies. These changes are caused by involvement of the adjacent proximal nail matrix. Hyponychium involvement results in severe subungual hyperkeratosis and nail bed splinter hemorrhages.

There are multiple causes of allergic contact dermatitis of the nails. A careful history can elicit allergens that commonly come into contact with the fingers. Workers in certain occupations, such as hair dressers, manicurists, dental workers, fiberglass workers, printers, and glue workers, are at high risk for developing irritant as well as allergic contact dermatitis. Common allergen-containing products include sunscreens (oxybenzone [benzophenone-3]), cosmetics, soaps, and dyes.

A history may elicit exposure to long-lasting nail polishes containing methacrylates. Methacrylates can also be found in dental products and hard plastics. Formaldehyde, which is found in nail hardeners, is another cause of contact dermatitis. Foods can rarely cause allergic contact dermatitis. Efinaconazole can also cause contact dermatitis.

Per February 2019, isobornyl acrylate was named the "contact allergen of the year" by the American Contact Dermatitis Society. It is an acrylic monomer often used as an adhesive. Acrylic nails are a potential source. Clinician awareness is important, because testing using routine panels does not identify isobornyl acrylate.

Related topic: Hand dermatitis