Depending on their depth and the layers of skin affected, burns are divided into 3 categories:
- 1st degree:
The damage extends only to the uppermost layer of the skin (e.g. sunburns). These are superficial burns affecting only the epidermis.
- 2nd degree:
The damage extends beyond the upper and middle layers of the skin and blisters appear. They are partial-thickness burns and involve the epidermis and the choroidal part of the skin. They usually heal within three weeks with appropriate treatment.
- 3rd degree:
The destruction of the skin in the area is total. It is a full-thickness burn and involves the epidermis and the dermis, and the depth of the burn extends to the subcutaneous fat.
In addition to the depth of the burn, the extent in terms of total body surface area is an important predictor of the outcome of the burn. It is calculated as a percentage of total body surface area and special calculation charts (Lund & Browder charts) are available to facilitate its calculation.
Another way of dividing burns is into epidermal (corresponding to those of grade A and B) and subcutaneous (grade C).