Symptoms of necrotizing fasciitis may develop quickly, often as soon as 24 hours after a minor skin injury. The rapid onset of symptoms is one of the most important clues that you may need immediate medical care. Another common feature of this disease is pain that is greater than you would expect from the wound or injury.

Necrotizing fasciitis most commonly affects extremities, particularly the legs, but can affect any part of the body. When necrotizing fasciitis occurs in the area of the genitals, it is called Fournier gangrene.

The most common early symptoms include:

• Sudden, severe pain in the affected area.
• Fever, nausea, vomiting, fatigue, and other flu-like symptoms.
• Redness, heat, swelling, or fluid-filled blisters in the skin over the affected area. If the infection is deep in the tissue, these signs of inflammation may not develop right away.

Later symptoms may include:

• Signs of shock (including confusion, fainting, or dizziness), which are often worse when you get up from sitting or lying down. These symptoms are caused by a drop in blood pressure.
• Scaling, peeling, or discolored skin over the affected area, which are signs of tissue death, or gangrene.

A common entry point for the bacteria is through a wound such as a burn, cut, scrape, or insect bite. Within 24 hours after the bacteria have entered the wound, swelling, heat, redness, and tenderness spread quickly from the original wound site. Within 24 to 48 hours after spreading, the redness may darken to purple and then to blue. Blisters containing yellow fluid may also form. Within 4 to 5 days after the initial infection, gangrene develops. Within 7 to 10 days, dead skin separates from healthy skin as the infection continues to spread into other tissue. Certain strains of bacteria (such as streptococci) can be more aggressive, shortening the entire process to 2 to 4 days.