Cellulitis is a bacterial infection of the deepest layers of your skin. It is usually caused by group A streptococcus, the same bacterium that leads to strep throat. But it may also be due to Staphylococcus aureus, such as MRSA, and other types of bacteria. Symptoms of cellulitis include a red, swollen, and painful lump or area on your skin. It most often affects the legs, arms, or face, but can develop anywhere on the body. If the infection spreads throughout your body, you may feel tired and have chills. Cellulitis can be a serious condition. Follow the links below to find WebMD's comprehensive coverage on how cellulitis develops, what it looks like, how to treat it, and much more.