Erysipelas is a skin infection. It is a form of cellulitis, but unlike cellulitis, which affects deeper tissue, erysipelas only affects the upper layers of the skin. However, the two conditions can overlap, which can make it hard for a doctor to tell the two conditions apart. Previously, doctors thought that erysipelas only affected the face, but the National Organization for Rare Disorders now estimate that around 80 percent of all cases occur on the legs. It can also appear on the arms and torso. Erysipelas is usually caused by the Group A Streptococcus bacterium, the same bacterium that causes strep throat. The infection results in large, raised red patches on the skin. This is sometimes accompanied by other symptoms, including blisters, fevers, and chills. Erysipelas most frequently occurs on the face and legs. Erysipelas often improves with treatment. The infection can usually be treated effectively with antibiotics.