Burns are injuries to the skin due to heat, cold, chemicals, friction, electricity, or radiation. Burns are classified into several different types, depending upon the layers of skin involved and their appearance, severity, and prognosis.
- When only the epidermis is injured, the burn is described as a superficial, first-degree burn. First-degree burns appear red but have no blisters, and they generally heal well without intervention.
- When the injury extends into the upper layers of the dermis, the burn is described as a superficial, partial-thickness, or second-degree burn. These burns appear red, with clear blisters. Although local infection is a risk, these burns typically heal well with no scarring. Some second-degree burns may be more severe and extend into the deep layers of the dermis. These burns are described as deep partial-thickness burns. While they are still considered second-degree, they may result in scarring and may require skin grafts, a procedure where healthy skin is transplanted to a new location.
- Burns that extend throughout the entire epidermis and dermis are described as full-thickness or third-degree burns. These burns may appear stiff and white or brown, may produce significant scarring, and may never fully heal.
- Finally, burns that extend through the entire skin and into the underlying tissues are described as fourth-degree burns. These burns appear black or charred, and they may require amputation. Fourth-degree burns can be fatal.
When burns are extensive, the body is at high risk of infection and dehydration. When a person is burned and depending on the severity of burn, the blood vessels, including the capillaries, may be affected. Combined with the release of chemical substances into the blood, this will lead to increased capillary permeability to fluids, leading to the leaking of fluids from the blood vessels into the tissues. The higher the percentage of burned skin, the more severe the loss of fluid will be and the greater the dehydration will be. In a third-degree burn, the entire thickness of skin (epidermis and dermis) is involved, and nerve endings have been destroyed. The body's barrier against water loss is no longer there. Unless fluids are replaced immediately, renal shutdown could occur.
Skin is both a physical barrier, preventing water loss, and a chemical barrier, preventing the growth of bacteria. The damaged skin has openings in it through which bacteria and other pathogens could enter the body. If this is the case, skin grafts may be used to seal the openings. There are two types of skin grafts, split-thickness skin grafts and full-thickness skin grafts. Split-thickness skin grafts include the epidermis and only part of the dermis. This type of graft can cover a large area of skin, and it has a lower risk of rejection. The donor site must heal through reepithelialization, when keratinocytes migrate into the new tissue to strengthen it. Full-thickness skin grafts include the epidermis and the entire dermis. There is a higher risk of rejection with full-thickness grafts, but the donor site may be sutured, leaving a scar line that heals more easily.