Burns may be caused by heat generated by radioactive, chemical, or electrical agents. Two factors affect burn severity: the depth of the burn and the extent of the burned area. There are three categories of burns:

First-degree burns—Burns that are red and painful, but not swollen and blistering, such as from a sunburn, and damage only the epidermis.

Second-degree burns—Burns that are red, painful, and blistering, these burns involve injury to the epidermis and the upper region of the dermis.

Third-degree burns—Burns that are severely painful, giving the skin a white or charred appearance; they destroy all layers of the skin, including blood vessels and nerve endings. Skin damaged by third-degree burns does not regenerate. Damage to the skin affects the body’s ability to retain fluids.