Usually a reactive lymph node from a nearby ear or scalp issue, or a benign skin cyst. Hard, fixed, growing, or 4+ weeks means get it checked; fever with ear pain and swelling is urgent.
What to do
Common questions
What does a lump behind my ear mean?
A lump behind the ear is usually one of two harmless things. The first is a swollen lymph node - there is a chain of them right behind the ear that reacts to anything inflamed nearby: an ear infection, a scalp irritation, even aggressive earbuds or a pierced-ear problem. These feel like tender, movable peas and shrink over a few weeks once the cause settles, per MedlinePlus guidance on swollen nodes. The second is an epidermoid or pilar cyst - a smooth, round, slow-growing bump under the skin that has likely been there for months. Cysts are benign and only need attention if they get red, painful, or start draining. A third common one in children: a small lump on the bone itself that appeared after a bump is often just a healing knot from the injury. What earns a visit: a lump that is hard and fixed, keeps growing, or hangs around past four weeks; redness, warmth, and pain that suggest an infected cyst or abscess needing drainage; fever with ear pain and swelling that pushes the ear outward - that combination, mastoiditis, is urgent; and any lump with hearing changes or facial weakness. Pymander is a free AI doctor, 24/7 by text. Describe the lump and how long it has been there, and it can help you decide watch versus book.