Melanocytic naevi(moles) are localised benign clonal proliferations of melanocytes.Their cause is unknown but may relate to abnormalities of the normal migratory pattern of melanocytes during developement.It is quite normal to have 20-50 although,interestingly,individuals with red hair have fewer.

Genetic and environmental factors are implicated.Monozygotic twins have higher concordance in naevi numbers than dizygotic twins.Individuals who have had greater sun exposure have higher numbers of naevi.most melanocytic naevi appear in childhood and early adult life,or during pregnancy or oestrogen therapy.The onset of a new mole is less common after the age of 25 years.Congenital melanocytic naevi occur at or shortly after birth.

Clinical features

Acquired melanocytic naevi are classified according to the microscopic location of the melanocyte nests.Junctional naevi are usually macular circular or oval,and mid-to dark brown.Compound and intrader mal and may be hair-bearing.Intradermal naevi are usually less pigmented than compound naevi.Their surface may be smooth,cerebriform,hyperkeratotic or papillomatous.