A bathing trunk nevus is a dark colored, often hairy patch of skin that is present at birth.

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

Bathing trunk nevus may occur with:

• Growth of fatty tissue cells (lipomas)
• Neurofibromatosis
• Other nevi
• Spina bifida

The risk of this condition is thought to be 3 - 7%.

• Dark-colored patch of skin covering a large area of the middle body or arms and legs
  • Brown to bluish-black color
  • May contain hair
  • Skin may be smooth to wart-like

All birthmarks should be evaluated by your health care provider. A biopsy of suspicious areas may be obtained for examination to determine if the cells have become cancerous. An MRI of the brain might be performed.

Treatment consists of surgery to remove the nevus. Skin grafting is done when necessary. Extremely large nevi may be removed in several stages. Although surgical removal is the treatment of choice, lasers can also be used to improve the appearance.

Steroid medications may be used, but they can have side effects.

Psychological treatment can help with the emotional impact of having a disfiguring disorder.

Bathing trunk nevi are not serious, unless the nevus turns into skin cancer (malignant melanoma).

• Depression and other emotional problems (due to appearance)
• Skin cancer (melanoma)

Rarely, bathing trunk nevi occur with a condition that causes a growth of pigment-producing cells in the head (leptomeningeal melanocytosis). Complications include:

• Hydrocephalus
• Motor abnormalities
• Seizures

This condition is usually diagnosed at birth. Call for an appointment with your health care provider (or mention it during a well-baby exam) if your child has a large pigmented area anywhere on the skin.