
Erythema nodosum (EN) is an inflammatory skin condition causing tender, red or purplish, painful bumps (nodules) usually on the shins, but also thighs, arms, or ankles, often appearing suddenly. It's a hypersensitivity reaction to infections (like strep), medications (birth control), or underlying conditions (Crohn's, sarcoidosis) but can have no known cause (idiopathic). While usually self-limiting, resolving in 3-6 weeks, treatment focuses on symptom relief and addressing the root cause, with symptoms fading like bruises.