The etiology of erythema gangrenosum is currently unknown. Primary causes are unclear; secondary causes include myeloproliferative and autoimmune disorders, multiple sclerosis, spinal cord disease, infections, and drug and mushrooms poisoning; and hereditary causes are autosomal dominant disorders with a family history. Erythema multiforme is a rare paroxysmal vasodilatory disorder of unknown etiology. It is characterized by paroxysmal elevation of skin temperature, flushing, and swelling of the skin of the extremities, and produces severe burning pain, especially in the toes and soles of the feet, which can be triggered or exacerbated by elevated ambient temperatures, and relieved by lower temperatures. The etiology and pathogenesis of the disease are unknown. The disease is usually categorized into primary erythema gangrenosum, secondary erythema gangrenosum and hereditary erythema gangrenosum. Primary erythromelalgia may begin at any age. Secondary erythromelalgia is more common in myeloproliferative disorders (e.g., erythrocytosis, thrombocytosis, etc.) and autoimmune disorders, as well as multiple sclerosis, spinal cord disease, diabetes mellitus, AIDS, infections, and certain medications and mycotoxicoses. Erythromelalgia is an autosomal dominant disorder with a family history of erythromelalgia. Studies have shown that mutations or abnormalities in the expression of the genes of the sodium channel subunits are associated with the disease. It is recommended that patients with erythema nodosum go to the hospital in time, under the guidance of the doctor to standardize the treatment, do not blindly use drugs, so as not to cause adverse consequences.