A bump on the back of your head usually has a harmless explanation. It could be a normal part of your skull’s anatomy, a cyst, a swollen lymph node, or a soft tissue growth. In most cases, the bump is benign and either resolves on its own or stays unchanged for years without causing problems. What matters most is how it feels, how fast it appeared, and whether it came with other symptoms.
It Might Just Be Your Skull
Before assuming something is wrong, it’s worth knowing that the back of your skull has a natural bony ridge called the external occipital protuberance. This is a small, hard knob right at the center-back of your head, near the base of the skull. Everyone has one, but in some people it’s more pronounced. When it’s especially prominent, it’s sometimes called an occipital spur or occipital knob. This is more common in men and is considered a normal anatomical variation, not a medical condition.
If the bump you’re feeling is hard, fixed in place (doesn’t move when you press it), painless, and sits right along the midline of the back of your skull, there’s a good chance you’re simply feeling bone that’s always been there. Many people don’t notice it until they happen to touch that spot or get a short haircut.
Cysts on the Scalp
Pilar cysts are the most common type of skin cyst, and they overwhelmingly favor the scalp. They occur in less than 10% of the population but account for more scalp lumps than any other cyst type. These are round, firm, smooth bumps that sit just beneath the skin. They grow extremely slowly, sometimes taking years to reach a noticeable size, and they’re usually painless unless they become inflamed or infected.
A pilar cyst is filled with a protein called keratin (the same material your hair and nails are made of). When you press on one, it feels firm and rubbery and doesn’t move much. You may have one or several at the same time. They’re not dangerous, though some people choose to have them removed if they become large or bothersome. If a cyst suddenly turns red, warm, or painful, that’s a sign it may be infected and worth getting checked.
Swollen Lymph Nodes
There are lymph nodes at the base of your skull called occipital lymph nodes. When your body is fighting an infection, nearby lymph nodes swell as they ramp up their immune response. A bump that appears quickly, feels tender, and sits just behind or below the bony ridge at the back of your head is likely a swollen lymph node.
Upper respiratory infections are the leading cause of swollen lymph nodes. Common colds, the flu, sinus infections, ear infections, and minor skin infections on the scalp can all trigger swelling in the nodes at the back of your head. The swelling typically goes down as the infection clears, usually within a few days to a couple of weeks. A lymph node that stays swollen for more than two weeks, keeps growing, feels hard and fixed in place, or appears without any obvious infection is worth having a doctor evaluate.
Lipomas and Fatty Lumps
Lipomas are soft, painless lumps made of fatty tissue that sit just under the skin. They’re one of the most common benign soft tissue growths. On the back of the head, a lipoma feels distinctly different from a cyst or a bony bump. It’s soft (almost doughy), moves easily when you push on it, and doesn’t cause any skin changes on the surface. Doctors sometimes identify them by the “slippage sign,” where the lump seems to slip out from under your fingers when you press the edge.
Lipomas grow slowly, rarely cause pain, and almost never become cancerous. Most people leave them alone unless the lipoma is large, cosmetically bothersome, or in a spot where it gets irritated.
Folliculitis and Infected Hair Follicles
If the bump is red, tender, and closer to the skin surface, it may be an inflamed or infected hair follicle. Folliculitis is extremely common on the back of the head, especially along the hairline. It looks similar to acne: small red or white pus-filled bumps that may itch or sting. The most frequent culprit is staph bacteria getting into a hair follicle.
A single infected follicle can sometimes develop into a deeper, more painful lump called a boil (furuncle), which fills with pus over several days before draining. When multiple boils cluster together, they form a carbuncle, which is larger and more painful. Mild folliculitis often clears on its own with good hygiene and warm compresses. Boils and carbuncles that don’t drain or keep coming back may need medical attention.
Osteomas: Bony Growths on the Skull
An osteoma is a benign, slow-growing bony tumor that develops on the skull. Unlike the natural occipital protuberance you’re born with, an osteoma is a new growth of bone that forms over time. Many osteomas are small and produce no symptoms at all. They’re frequently discovered by accident during imaging done for something else entirely.
On the back of the head, an osteoma feels like a hard, immovable lump that’s clearly part of the bone rather than sitting on top of the skin. If one stays small and symptom-free, the typical approach is simply monitoring it with periodic imaging. Large osteomas can occasionally cause headaches or pressure, but this is uncommon when they’re on the back of the skull rather than near the sinuses.
Bumps From a Head Injury
If you recently hit the back of your head and a bump appeared, you’re probably dealing with a “goose egg,” which is a pocket of blood and fluid that collects under the scalp after impact. The scalp has a rich blood supply, so even minor bumps can produce impressively large, tender swelling. These look alarming but are usually superficial. Applying a cold compress and giving it a few days is typically enough.
What matters more than the bump itself is how you feel afterward. Seek emergency care if a head injury is followed by loss of consciousness (even briefly), a headache that keeps getting worse, repeated vomiting, seizures, confusion, weakness or numbness in the hands or feet, clear fluid draining from the nose or ears, or unequal pupil sizes. In children, watch for persistent inconsolable crying, unusual drowsiness, or seizures. These are signs of a possible traumatic brain injury and need immediate evaluation.
How to Tell What You’re Dealing With
A few simple observations can help you narrow things down before you see a doctor:
- Hard and immovable, right at the center: likely your natural occipital protuberance or, less commonly, an osteoma.
- Firm, round, and smooth under the skin: likely a pilar cyst, especially if it’s been there a while and is painless.
- Soft, doughy, and slides under your fingers: likely a lipoma.
- Tender, appeared quickly, you’ve been sick: likely a swollen lymph node.
- Red, warm, near the skin surface, possibly with pus: likely folliculitis or a boil.
- Appeared right after hitting your head: likely a goose egg from trauma.
Most bumps on the back of the head fall into one of these categories and don’t require urgent treatment. A bump that grows rapidly over weeks, feels rock-hard and irregular, is painless but keeps getting bigger, or comes with unexplained weight loss or night sweats deserves prompt medical evaluation. The same goes for any post-injury bump accompanied by neurological symptoms. For everything else, a routine visit to your doctor can confirm what you’re feeling and put your mind at ease.