Monarch Disease Ontology id MONDO_0013688 (linear and whorled nevoid hypermelanosis) (LWNH) is a rare skin condition characterized by swirling streaks of hyperpigmented (darkened) skin. The pigmentation follows the lines of Blashko and is mainly located on the trunk and limbs. It is present at birth or appears in the first few weeks of life. It typically progresses for one to two years and then stabilizes. Hyperpigmentation is usually the only symptom but there are isolated reports of other symptoms, involving mostly the central nervous system, musculoskeletal system, and heart. While most cases of LWNH are sporadic, apparent genetic transmission rarely has been described. A few people with LWNH have been diagnosed with chromosomal mosaicism. Also known as: Becker Nevus, Becker's Nevus, linear papular ectodermal-mesodermal hamartoma, melanosis Neviformis, pigmented hairy Epidermal Nevus, pigmented hairy Nevus of Becker, progressive cribriform and zosteriform hyperpigmentation.