Nevi (or moles) are very, very common. They are generally well-circumscribed dark spots (or “papules” to use the dermatological terminology) that can appear at any time in someone’s life.
Histologically they are composed of groups of melanocytic nevus cells and can be found in the epidermis, dermis or both.
The problem with nevi is that they are pigmented and people tend to get worried about pigmented things on the skin (for good reason as melanoma can be a pretty scary disease).
Common acquired nevi are grouped into three categories (I’ll leave out congenital and dysplastic nevi for now)
- Junctional: the nevus cells are completely in the epidermis, just above the dermal-epidermal junction. Clinically they are <1 cm, flat or minimally elevated and dark in colour.
- Compound: the nevus cells are in both the epidermis and the papillary dermis (top layer of the dermis), and cross the basement membrane. Clinically they are raised, and a medium-brown colour.
- Dermal: the nevus cells are completely in the dermis. Clinically they are raised and almost always pigment less as the cells lose their capacity for melanization when in the dermis. They usually have telangectasia and may or may not have hair. They don’t tend to appear until the 2nd or 3rd decades of life.