This information is provided by the National Institutes of Health (NIH) Genetic and Rare Diseases Information Center (GARD).
Becker’s nevus is a non-cancerous, large, brown birthmark occurring mostly in males. It can be present at birth, but is usually first noticed around puberty. It typically occurs on one shoulder and upper trunk but occasionally occurs elsewhere on the body. A Becker’s nevus often becomes darker, and excessive hair growth (hypertrichosis) and acne may develop within the nevus.
Becker’s nevus is due to overgrowth of the epidermis (upper layer of the skin), pigment cells (melanocytes) and hair follicles. The specific underlying cause is unknown. Because it often forms around puberty in males and is sometimes associated with acne and hair growth, its development may be triggered by androgens (male sex hormones such as testosterone).
Treatment is primarily for cosmetic reasons (hyperpigmentation or hair growth) and may include Ruby laser treatment or laser-assisted hair removal.
In very rare cases, Becker’s nevus is associated with other skin features; muscular or skeletal features; or underdevelopment (hypoplasia) of the breast. When this occurs, the condition is known as Becker’s nevus syndrome.
For more information, visit GARD.