Cellulitis is the medical term for bacterial infection of the skin. This infection causes redness, heat and pain in the affected area. Cellulitis may appear after an injury that you remember or may seem to appear out of nowhere. If left alone, cellulitis can progress into a serious infection even spreading to the bloodstream. While cellulitis can appear anywhere on the body, it is most common on the legs. The two most common bacteria causing cellulitis are staphylococcus and streptococcus. ...