 Burns that affect only the superficial skin layers are known as superficial or first @-@ degree burns . They appear red without blisters and pain typically lasts around three days . When the injury extends into some of the underlying skin layer , it is a partial @-@ thickness or second @-@ degree burn . <unk> are frequently present and they are often very painful . Healing can require up to eight weeks and scarring may occur . In a full @-@ thickness or third @-@ degree burn , the injury extends to all layers of the skin . Often there is no pain and the burn area is stiff . Healing typically does not occur on its own . A fourth @-@ degree burn additionally involves injury to deeper tissues , such as muscle , tendons , or bone . The burn is often black and frequently leads to loss of the burned part . 
