Erythema nodosum is an inflammation in the subcutaneous fat triggered by an immunological reaction. The nodules are clearly palpable, sore and burning knobs. The fierce reddening turns into bruising as the healing progresses. The nodules will heal without leaving scars. The patient often feels ill, and fever may also be present. Infections caused by streptococcus or yersinia, and sarcoidosis are the most common triggering factors.