Necrotizing skin infections include necrotizing cellulitis and necrotizing fasciitis, which are severe cellulitis characterized by necrosis of infected tissue. The affected skin is red, the surface is hot, and sometimes swollen and bubbles form under the skin. The patient usually feels very uncomfortable around the body and has high fever. Treatment includes removal of the necrotic skin, which may sometimes require extensive surgical excision and intravenous antibiotics. Most skin infections do not result in necrosis of the skin and surrounding tissues. However, sometimes bacterial infections can cause blockage of small blood vessels in the infected area. The blockage causes necrosis of the tissue supplied by these vessels due to ischemia. It is difficult to control the rapid spread of the infection because the body’s immune defenses (such as white blood cells and antibodies), which function through the blood system, cannot reach the area. Even with appropriate treatment, necrosis can occur. Some necrotizing skin infections spread deep in the skin along the surface of the muscle (fascia) and are called necrotizing fasciitis. Other necrotizing skin infections that spread in the outer layers of the skin are called necrotizing cellulitis. A variety of different bacteria can cause necrotizing skin infections, such as streptococci and clostridia, although most patients are caused by a combination of bacteria. A particular streptococcal infection has been reported as a “flesh-eating disease,” although it is not very different from other streptococcal infections. Some necrotizing skin infections begin with puncture wounds or avulsions, especially those contaminated with soil and debris. Other infections originate from surgical incisions or healthy skin. Sometimes patients with diverticulitis, intestinal perforation, or intestinal tumors develop necrotizing infections in the abdominal wall, genital area, or thighs. This infection occurs when certain bacteria escape from the intestine and spread to the skin. The bacteria can initially form an abscess in the abdominal cavity and spread directly outward to the skin or spread through the bloodstream to the skin and other organs. The initial symptoms usually resemble cellulitis. The skin is initially pale in appearance, but soon becomes red or bronze, burning to the touch, and sometimes swollen. Subsequently, the skin turns purple, often accompanied by fluid-filled blisters that are brown, watery, and sometimes foul-smelling. The skin in the necrotic area turns black (gangrene). Certain types of infections (including those caused by Clostridium difficile and mixed bacterial infections) produce gas. These gases form bubbles under the skin and sometimes the gas itself is in the blister and when squeezed the skin feels like it will break easily. The affected area initially feels painful, but as the skin necroses and the nerves lose function, the affected area loses sensation. Patients are usually symptomatic, with high fever, tachycardia and mental decompensation (from confusion to unconsciousness). Blood pressure drops (toxic shock) due to the release of toxins from the bacteria and the body’s response to infection-to-infection. The diagnosis of necrotizing skin infection can be made by the physician on the basis of clinical manifestations, especially the presence of subcutaneous gas. x-rays show subcutaneous gas very well. If a specific bacterial infection is involved, laboratory analysis of infected body fluids and tissue specimens is required. However, the physician should initiate treatment before identifying the causative organism. The overall mortality rate of this disease is approximately 30%. The prognosis is worse in elderly patients with other medical conditions and in those with advanced disease. Delays in diagnosis and treatment and inadequate excision of necrotic tissue can affect the prognosis. Necrotizing fasciitis should be treated by surgical excision of necrotic tissue coupled with intravenous antibiotics. Often a large amount of skin, tissue, and muscle must be removed, and in some cases, amputation may be necessary if the arm or leg is infected. Some physicians believe that hyperbaric chamber therapy can be given, but the efficacy is not yet clear.