Melanosis

**Semantic type:** Finding

**Definition:** A benign congenital or acquired lesion that arises from mucosal sites and is characterized by melanin pigment deposition in the basilar keratinocytes. It may be associated with a slight proliferation of junctional melanocytes. It presents as a single or multiple pigmented macules or patches in the external genitalia, anorectal region, distal urinary tract, and oral cavity.