In medicine, a burn is a type of injury to the skin caused by heat, electricity, chemicals, or radiation (an example of the latter is sunburn).
In classical medical literature, there were six degrees, the first three of which are still commonly used by the public:
First-degree: burns are usually limited to redness (erythema), a white plaque and minor pain at the site of injury. These burns usually extend only into the epidermis.
Second-degree: burns additionally fill with clear fluid, have superficial blistering of the skin, and can involve more or less pain depending on the level of nerve involvement. Second-degree burns involve the superficial (papillary) dermis and may also involve the deep (reticular) dermis layer.
Third-degree: burns additionally have charring of the skin, and produce hard, leather-like eschars. An eschar is a scab that has separated from the unaffected part of the body. Frequently, there is also purple fluid. These types
of burns are often painless (insensate) because nerve endings have been destroyed in the involved areas.
A cold burn is a kind of burn which arises when the skin is in contact with a low-temperature body. They can be caused by prolonged contact with moderately cold bodies (snow for instance) or brief contact with very cold bodies such as dry ice, liquid helium or liquid nitrogen, which are used in the process of wart removal. In such a case, the heat transfers from the skin and organs to the external cold body (as opposed to most other situations where the body causing the burn is hotter, and transfers the heat into the skin and organs). The effects are very similar to a "regular" burn. The remedy is also the same as for any burn: for a small wound keep the injured organ under a flow of comfortably temperatured water; the heat will then transfer slowly from the water to the organs and help the wound. Further treatment or treatment of more extended wound also as usual.