Burns on the human body are classified into three different degrees: first, second, and third degree. First degree burns are the least severe, while third degree burns are the worst.
All burns generally come from exposure to extreme heat, which may include hot liquids like boiling water or cooking oil, from a sunburn, or from a fire. It is also possible to be burned by severe cold; these burns look much the same and are treated in similar methods to burns from severe heat. The variation in degrees of burns from one case to another can depend on the degree of heat or coldness, the physical proximity to the heat or cold source, and the amount of time exposed to the source.
The most minor burns only extend to the top layer of skin, the epidermis, which means that they will generally not leave a permanent scar. These burns can occur when a person momentarily touches a hot object like a stove or a radiator, but does not hold his or her body to the object long enough to sustain serious damage. The result of a first degree burn will be a temporary redness and soreness in the area affected.
Somewhat more serious is the second degree burn, which causes immediate redness and, within a day or two, will result in a blister that fills with pus. Unlike the other degrees of burns, second degree burns may be more or less painful depending on whether the burn affects the nerves.
The most severe type, the third degree burn, always causes lasting damage. In the most serious cases, the skin is charred and will separate from the body in a type of scab called an eschar. The victim is not in pain because the burns have destroyed the nerve endings in the skin. In cases where a person has received third degree burns and survived, cosmetic reconstructive surgery is often necessary, where a graft of skin will be taken from a healthy part of the person's body and stitched into a burned area.
By some accounts, there are three other degrees of burns, though they are not commonly discussed. Burns where the skin is irreparably damaged can be called fourth degree burns, burns where the muscle beneath the skin is also lost are called fifth degree burns, and burns where the bone itself is charred are called sixth degree burns.