noun, plural: naevi
A pigmented area in the skin which may be congenital or acquired
A naevus is a pigmented area in the skin and is often associated with benign skin lesions. It is sometimes used synonymously with a birthmark (or a mole) since etymologically it is the Latin for birthmark. However, in stricter sense, it is more inclusive than birthmarks. A birthmark is a discoloration in the skin that is often present at birth (congenital). A naevus is similarly a pigmented area in the skin that may be congenital or acquired, i.e. forming later at life. Furthermore, the term naevus is a medical term to refer to any raised, coloured chronic lesion of the skin or the mucosa. It may pertain to any skin pigmentation disorder either involving an increased melanin (hypermelanotic) or a decreased melanin (hypomelanotic). Thus, naevi may be classified into two groups based on the melanin content. Examples of hypermelanotic naevi that are acquired include acquired melanocytic naevus, atypical naevus, becker's naevus, blue naevus, Hori's naevus, naevus spilus, spitz naevus, etc. Congenital hypermelanotic naevi include congenital melanocytic naevus, naevus of Ito, and naevus of ota. Acquired hypomelanotic naevi is exemplified by naevus anemicus. Congenital hypomelanotic naevi include naevus depigmentosus, epidermal naevi, connective tissue, naevi, and vascular naevi.