Becker's nevus

Becker's nevus (also known as "Becker's melanosis," "Becker's pigmentary hamartoma," "Nevoid melanosis," and "Pigmented hairy epidermal nevus") is a skin disorder predominantly affecting males. The nevus generally first appears as an irregular pigmentation (melanosis or hyperpigmentation) on the torso or upper arm (though other areas of the body can be affected), and gradually enlarges irregularly, becoming thickened and often hairy (hypertrichosis). The nevus is due to an overgrowth of the epidermis, pigment cells (melanocytes), and hair follicles. This form of nevus was first documented in 1948 by American dermatologist Samuel William Becker (1894–1964).