Gangrene is the death of an area of the body usually due to loss of blood supply or from a bacterial infection. It is of two types; dry gangrene which is caused by decrease in blood flow to a particular area of the body and wet gangrene is caused by bacterial infection that has not been treated.
1. Wet gangrene is usually caused by an injury such as a cut or open wound that becomes infected with bacteria. The infection gets full of pus and does not drain well, blocking off the blood supply and the oxygen to that part of the body, soon the tissue dies. If left untreated the area will become shrunken and black and could continue spreading to other parts of the body. Treatment with antibiotics to kill the bacteria is often necessary and surgically removing the blackened tissue will cease the spread of the infection. Amputation is rarely necessary if caught in the early stages. Disinfecting and keeping wounds clean can prevent them from turning into gangrene.

2. Dry gangrene is caused by the blood flow being stopped or reduced to an area of the body from an injury or disease. This area becomes oxygen deprived and turns black and shrinks when the tissue dies. Dry gangrene can be caused by an injury which cuts off the supply of blood. An injury can be a blunt trauma, usually to the toes or feet. When this kind of trauma occurs it may involve an acute arterial obstruction, blocking the blood supply. He signs are pain, red and swollen area. Surgery may be needed to unblock the arterial obstruction. Sometimes dry gangrene can be caused by frostbite. The area becomes so cold it gets deprived of oxygen and dies. Frostbite gangrene will not spread to other parts of the body. With frostbite you may feel numbness in the area but when the flesh dies it will become very painful. Once the tissue is dead it will be numb again and darken over time.
Other causes of dry gangrene are diabetes due to poor circulation of the blood to the extremities. Also, any kind of disease with poor circulation, hardening of the arteries, AIDS or arterial embolism can cause gangrene.
 The signs that dry gangrene is beginning are a dull, aching pain and coldness in the area. The area may get a sickly pallor to it. If gangrene is developing slowly it can be reversed by surgery. Treatment of poor circulation to prevent tissue from dying can be done in a hyperbaeric oxygen chamber prior to gangrene setting in. The patient goes into a chamber with richer oxygen level than we normally breathe to quickly oxygenate the blood. Treatment in the chamber is usually done once a day for months at a time. But it is difficult to get it done.