Diseases & Conditions

Bathing Trunk Nevus

Overview, Causes, & Risk Factors

A bathing trunk nevus is a large, pigmented, molelike birthmark. It covers an extremely large area of the body, often in the area covered by a pair of bathing trunks. It is often covered with hair.

What is going on in the body?

A collection of mole, or nevus, cells forms a very large brown mole during fetal development. The bathing trunk nevus is present at birth.

What are the causes and risks of the condition?

Although the cause of bathing trunk nevus is unknown, there may be a hereditary factor in some cases.

Symptoms & Signs

What are the signs and symptoms of the condition?

Symptoms of a bathing trunk nevus may include:

  • a brown molelike birthmark covering an extensive area of the trunk or legs
  • color varying from brown to blue-black
  • hair growing from the mole
  • smaller lesions near the large mole
  • surface texture varying from smooth to warty

  • Diagnosis & Tests

    How is the condition diagnosed?

    The healthcare provider can diagnose a bathing trunk nevus when he or she examines the characteristic birthmark. A biopsy may be done to determine if the cells have become cancerous.

    Prevention & Expectations

    What can be done to prevent the condition?

    There is no known prevention for a bathing trunk nevus.

    What are the long-term effects of the condition?

    A bathing trunk nevus may develop into melanoma, a particularly serious form of skin cancer. The cosmetic appearance may cause psychosocial problems.

    What are the risks to others?

    There are no risks to others.

    Treatment & Monitoring

    What are the treatments for the condition?

    The lesion must be carefully monitored for any changes in color or texture. Surgery to remove the nevus may be recommended to prevent the development of melanoma.

    What are the side effects of the treatments?

    Surgery may cause bleeding, infection, and allergic reactions to the anesthesia.

    What happens after treatment for the condition?

    After the nevus is removed, the area needs to be watched closely for signs of infection.

    How is the condition monitored?

    A bathing trunk nevus should be closely monitored by the healthcare provider. The affected person, or the family, should report any changes in texture or color to the healthcare provider.


    Author:Lynn West, MD
    Date Written:
    Editor:Crist, Gayle P., MS, BA
    Edit Date:05/28/02
    Reviewer:Gail Hendrickson, RN, BS
    Date Reviewed:10/01/01


    Skin Disorders: Mosby's Clinical Nursing Series, MJ Hill, 1994.