Erythema nodosum, if it causes swelling of the feet, is most often due to edema caused by the acute phase of inflammation. Erythema nodosum is mainly characterized by acute inflammation of the adipose tissue, which is commonly found in the thighs or calves or face and neck, and seldom involves the feet because there is little adipose tissue in the feet; a small amount of acute early stage may cause generalized edema involving the feet, which is rare. As the disease migrates, the edema will gradually resolve and usually requires no treatment. The pathogenesis of erythema multiforme has many factors, most of them are caused by infectious factors, drug factors or other immune factors, and the treatment needs to be targeted treatment. If you have erythema nodosum, it is recommended to go to the hospital in time.