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).

It is thought that it is due to a gene defect, which has not yet been identified. It may be triggered to develop by circulating androgens (male hormones such as testosterone), which is why it appears in males at puberty.

Features of Becker Nevus

A Becker naevus is a large one-sided brown patch, sometimes over half the upper back or chest. After puberty it often becomes darker and quite hairy, a feature also called hypertrichosis. Occasionally acne may develop in the naevus.

Beckers nevus syndrome

Rarely, like other birthmarks, there may be some abnormality of underlying tissues derived from the same embryonic cell type, the ectoderm. This is known as the Becker nevus syndrome. These abnormalities may include:

Smooth muscle hamartoma (overgrowth of smooth muscle tissue like a deep birthmark)
Under-development of underlying structures such as breast, pectoral muscle, fat, limb, chest wall, spine
Over-development of a tissue such as adrenal gland, limb, fingers or toes, scrotum.

Treatment of Beckers nevus

There is no effective treatment for the majority of Beckers nevi. However, the dark brown color is less obvious if the affected area is kept out of the sun so that it doesn't tan.

The excessive hairs can be reduced by repeated treatments with a hair removal laser or by electrolysis. The pigmentation can be reduced by a pigment laser, but this is not always effective and it may also be made worse by laser treatment.

Becker nevus-associated acne can be treated with standard acne therapies, including in severe cases, oral isotretinoin.