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Skin is the largest organ of the human body. Exposure to extreme heat, radiation, electrical shock or chemical agents can burn the skin causing pain, blistering, and, in severe cases, irreversible damage. The epidermis is the outermost layer of skin and the dermis is the middle layer, with the subcutaneous tissue lying beneath. Burns are classified as first-, second-, or third-degree burns depending on the amount and depth of tissue damage. A first-degree burn causes damage to the epidermis, causing pain, redness and some swelling. Typically, this type of burn will heal without scarring. A second-degree burn causes damage to the epidermis and the dermis, and this burn usually results in pain, redness and blistering. Third-degree burns are the most severe because the damage extends past the upper layers of skin to the sensitive subcutaneous tissue, destroying nerves, blood vessels, and other dermal components. Extensive third-degree burns can be fatal because the threat of infection is extremely high. In fact, bacterial infection is the leading cause of death in burn victims.