Wounds and burns can be categorized by their depth of penetration into the skin.
Superficial wounds or burns, previously known as first degree, are similar to sunburns and heal in a few days without any sequelae.
Partial thickness wounds or burns, previously known as second degree, will typically involve the epidermal skin layer while only partially damaging the dermal layer. The implications here are that the injury can heal spontaneously over several days to weeks by re-epithelialization from some of the hair follicles and glands within the dermis and will do so with no scar or minimal scarring.
Full thickness, previously called third degree, involve both the epidermis and the dermis and will not heal spontaneously without severe scarring and most often are treated by surgical excision and skin grafting. This type of treatment can lead to serious scarring of the wounded areas as well as the areas where the skin grafts are taken. Sometimes wound depth cannot be initially diagnosed clinically.