The severity of a cutaneous burn wound depends not only upon the depth of the burn but also upon the extent of the body surface area affected, which determines the loss of fluids and heat and therefore the impact on the major physiological systems of the body.
Burns which only injure the epidermis, such as mild sunburn, are known as first degree burns. They result in temporary erythema (redness), due to dilation of the capillaries, and oedema (swelling). Burns which extend into the living layer of the skin, the dermis, are much more serious. It is common to distinguish between second degree, or partial thickness, burns, and third degree, or full thickness, burns. Second degree burns are those in which necrosis extends into the dermis, but with the survival of a sufficient foundation of such skin appendages as sweat glands and hair follicles to ensure that the skin regenerates without having to heal from the edges of the wounds. Third degree, or full thickness, burns are those in which all the dermis is destroyed. In addition there may be destruction of the underlying fat, muscle, bone and other tissues. The terms fourth and fifth degree burns are sometimes used to describe such injuries.