Bathing trunk nevi are thought to be congenital, but in some families the frequent appearance of these lesions suggests a hereditary component.
The surface texture may vary from smooth to warty, and the color varies from brown to bluish black. Bathing trunk nevi may cause psychological (emotional) problems because of their cosmetic appearance.
More importantly, the nevus has a high risk of developing into malignant melanoma (a type of skin cancer). The risk is thought to be between 3% and 7%, although this number varies in different medical studies.
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