Determining the severity of a burn includes establishing how deep the damage goes into or through the skin. Burn thickness in most burn units is classified by degree -- the higher the number, the worse the burn.
First-Degree BurnsThis means a superficial burn. The surface of the skin is damaged, but the epidermis (the outermost layer of skin) is still intact, and therefore able to perform its functions (control temperature and protect from infection or injury). When determining severity, care providers ignore first-degree burns.
Second-Degree BurnsThis means damage that has extended through the epidermis and into the dermis (the second layer of skin). Second-degree burns also are known as partial-thickness burns. In determining the severity of burns, the presence of second degree burns indicates a loss of skin function.
Blisters are the first sign of a second-degree burn. As the epidermis is destroyed, it begins to separate from the dermis. Fluid builds beneath it, causing blisters. Eventually, the blisters will spread into one another until the very thin epidermis falls away, exposing the raw dermis underneath.
Once the epidermis has separated from the raw dermis, the victim begins to lose fluid, heat, and the ability to block infection. The raw nerve cells of the dermis also mean second degree burns are the most painful.
Third-Degree BurnsThis indicates the burn has destroyed both the epidermis and dermis. The victim has the same trouble with fluid loss, heat loss, and infection that come with second-degree burns. Full-thickness burns also cause nerve death, so the victim may not be able to feel anything in the area of the burn.
There's no easy way to tell the difference between a deep partial-thickness burn (2nd degree) and a full-thickness burn (3rd degree) when looking at it in the field, so we don't try. Instead, all burns that are deep enough to separate the epidermis from the dermis are counted when determining severity. In other words, we count all burns that are bad enough to form blisters - or worse - when assessing burn severity.