Gas gangrene is mainly caused by open trauma deep into the muscle being infected by anaerobic bacteria such as P. aeruginosa, which releases exotoxins and enzymes that produce large amounts of gas causing the tissue to swell and necrosis. These bacteria require an oxygen deficient environment to grow and multiply in the body, therefore, tissues with deep wounds are generally susceptible to infection, so infection does not occur in the general population when exposed to anaerobic bacteria and secretions from patients with gas gangrene.