Erythema nodosum has different causes and does not take exactly the same amount of time to treat, but usually takes 2-8 weeks or longer to cure. Erythema nodosum is most commonly characterized by erythema nodosum, which is usually classified as idiopathic or secondary. Idiopathic erythema nodosum is self-limiting, and even if the patient is left untreated, it can disappear after a natural course of 3-6 weeks, usually without scarring. If the patient is actively treated and rests in bed, the natural course of the disease will be shortened, and the disease will improve significantly in 2-3 weeks until it disappears. As for secondary erythema nodosum, it depends on the control of the primary disease. For infection-related erythema nodosum, such as streptococcal infection, the patient will usually have erythema nodosum gradually getting smaller and disappearing after 1-3 weeks of anti-infective drug treatment. However, for erythema nodosum caused by Mycobacterium tuberculosis infection, it usually becomes smaller after 1-2 months of treatment of the primary infection, and some patients even increase within 1 month of treatment, but the lesions will gradually subside with the prolongation of the treatment time. It is suggested that patients should pay attention to elevate the affected limbs during the treatment, minimize the activities, pay attention to rest and strengthen the nutritional therapy.