Cellulitis is a swelling of the soft tissue under the skin, which is caused by bacterial infection. The bacteria that cause cellulitis enter the body through cracks in the skin that result from, for example, insect bites, wounds, or burns. The bacteria that are most often responsible for cellulitis are Group A streptococcus and staphylococcus. Cellulitis creates redness, warmth, tenderness and swelling in the infected areas. If the infection is allowed to spread, it can attack muscle and bone and, in rare cases, it can kill living tissue. Cellulitis can ... cause enclosed collections of pus called abscesses, which must be drained to prevent further infection.