When gangrene affects the skin, signs and symptoms may include: 
Changes in skin color — ranging from pale gray to blue, purple, black, bronze or red
Swelling
Blisters
Sudden, severe pain followed by a feeling of numbness
A foul-smelling discharge leaking from a sore
Thin, shiny skin, or skin without hair
Skin that feels cool or cold to the touch
 If gangrene affects tissues beneath the surface of your skin, such as gas gangrene or internal gangrene, you may also have a low-grade fever and generally feel unwell. If the germs that caused the gangrene spread through the body, a condition called septic shock can occur. Signs and symptoms of septic shock include: 
Low blood pressure
Fever, although some people may have a body temperature lower than 98.6 F (37 C)
Rapid heart rate
Lightheadedness
Shortness of breath
Confusion
