First-degree burns, which are the least dangerous because they involve only the outer, epidermal, layer of the skin, usually do not require hospitalization. Thin as a sheet of paper, the epidermis consists of about five layers of cells. The cells in the deepest layers constantly reproduce, pushing older layers to the surface, where they slough off after two weeks or so. Thus while first-degree burns appear red and swollen and are painful to the touch, they usually heal on their own.

Second- and third-degree burns, the kind treated by the New York team, call for much more care and, often, extended hospital stays. Penetrating below the epidermis, second-degree burns reach into the upper layer of the dermis, a thin layer of cells 1 to 3 mm thick that contains blood vessels, nerves, hair follicles and sweat glands. This upper portion can slowly regenerate and heal if damaged. But if the burn is third degree and destroys the dermis down to fat and muscle, skin grafts are needed for effective healing.

When the skin suffers a deep third-degree burn, two major regulatory systems go awry. The body loses its ability to control its temperature, causing burn patients to shiver even in temperatures as high as 75[degrees]F. Consequently, burn-unit rooms are often kept around 90[degrees]F, and a burn team's first priority is to warm the patients with heated fluids or heat shields suspended above the patient's bed.