Definition of Bathing trunk nevus:

A bathing trunk nevus is a dark colored, often hairy patch of skin present at birth, which may cover an extremely large area of the body. Sometimes the disfiguration covers most of the middle of the body, the upper arms, and thighs.

Causes, incidence, and risk factors:

Bathing trunk nevi are thought to be caused by defects or problems that occur as a baby grows in the womb. But, in some families, the frequent appearance of the condition suggests that bathing trunk nevus may be inherited.

Bathing trunk nevus may be associated with other birth defects.

The skin may vary from smooth to wart-like, and the color can range from brown to bluish black. Bathing trunk nevi may cause emotional problems because of their appearance.

Bathing trunk nevi can develop into melanoma (a type of skin cancer). The risk is thought to be between 3-7%.