Aloe vera obtained from a plant whose leaves are filled with a jelly-like substance has been used medicinally for centuries. There is a salicylate component of aloe gel that inhibits one of the body's pain-producing agents. Another component called magnesium lactate can inhibit a body chemical known to produce itching. For these reasons, applying aloe gel topically seems to enhance the healing process of skin inflamed with frostbite, sunburn, or regular burns. It is thought that topical use of aloe gel can also aid the clearing of psoriasis plaques. While there is some evidence that topical use might help minor skins wounds heal, more medical research is needed in this area. Some evidence also suggests that aloe gel may have antibacterial and antifungal properties as well. Medical researchers in the United States have found in test animals that after severe blood loss, a small amount of a derivative of aloe vera gel given intravenously prolonged survival and increased body-wide oxygen consumption. The derivative is thought to decrease the resistance to blood flow in traumatized vessels and help oxygen to reach target tissues.