A congenital melanocytic naevus (or CMN) is a type of birthmark.
- Congenital = present at birth
- Melanocytic = to do with melanocytes. Melanocytes are cells in everyone’s skin and hair that produce the pigment melanin. This is what which gives us our hair and skin colour. The cells in a CMN look most like melanocytes and they produce pigment, so they are called melanocytic.
- Naevus = birthmark (the plural is naevi).
Though CMN means birthmark or mole at birth, in fact, not all of them are present at birth. Around 1% of CMN appear after birth, usually in the first year of life. They look exactly the same as the ones present at birth, but are called CMN “tardive”, which means “late”.