Ashy dermatosis (AD), or dermatosis cenicienta, is an acquired condition of unknown etiology characterized by asymptomatic blue-gray or gray-brown "ashy" macules and/or patches, most commonly symmetrically distributed on the neck, trunk, and proximal extremities.

Many consider AD and erythema dyschromicum perstans (EDP) synonymous. However, some use the term EDP to refer to the subset of patients who present with annular erythematous / inflammatory borders around the ashy macules and patches, which is usually an early finding.

AD is most common among individuals with skin phototypes III-IV and may present in any age group without any sex predilection. Lesions are usually asymptomatic but may be pruritic. Macules often enlarge and coalesce into patches over multiple weeks. Overall, AD is slowly progressive and does not typically regress in adults, but it may spontaneously resolve in children.

Pathogenetically, a cell-mediated immune reaction to antigens located in basal and mid-epidermal keratinocytes is postulated. No definitive cause has been identified; however, AD has been associated with certain exposures, including ammonium nitrate, oral radiographic contrast media, cobalt, enteroviral infection, HIV seroconversion, chronic hepatitis C infection, and whipworm infection.

An AD-like eruption from osimertinib has been reported. See drug-induced hyperpigmentation for discussion of drugs that may cause an AD-like reaction.