99% of people have nevi and any part of the skin can be affected. A nevus is a spot on the skin that can be: black, blue or brown, raised, smooth or growing with hairs. What causes a nevus is an accumulation of "melanocyte" cells that give colour to the skin. There are two types of nevus: congenital and acquired during growth. Reasons: sunlight, hormonal disorders. If a nevus develops, it is always advisable to consult a dermatologist: it may be larger than 20, the shape of the border or its colour changes, its size increases, etc.