Contact Dermatitis Caused by Topical Minoxidil: Allergy or Just Irritation

Topical minoxidil is the mainstay of treatment for androgenic alopecia and is also used off-label for other forms of hair loss. Despite its efficacy and favourable safety profile, the use of minoxidil is associated with various side effects, the most commonly reported of which is contact dermatitis. A clear distinction between allergic contact dermatitis and irritant contact dermatitis to minoxidil is critical for management of androgenic alopecia. This article presents a systematic review of the current literature, evaluating minoxidil-induced allergic contact dermatitis. Of the 251 records identified through the database search, a total of 21 studies were included in the review. Most patients presented with classic signs of contact dermatitis, including erythema, pruritus, and increased scaling of the scalp. Of the patients with positive patch tests, a total of 54 patients showed sensitization to minoxidil itself and 12 patients to vehicle components. Patients with suspected signs of contact dermatitis such as erythema, scaling, and pruritus after minoxidil application should undergo patch testing to confirm or exclude allergy. For the test, the differential reactivity of minoxidil in various vehicles should be considered. Patients who are sensitive to propylene glycol should be offered alternative minoxidil formulations.