A lump on the back of your head is almost always benign. The vast majority of scalp lumps turn out to be cysts, lipomas, swollen lymph nodes, or simply the natural bony ridge of your skull. In clinical studies, roughly 98 to 99% of skin and soft tissue lumps are non-cancerous. That said, the cause matters, and understanding what different lumps feel and act like can help you figure out whether yours needs attention.
The Bony Ridge That’s Always Been There
Before assuming something is wrong, it’s worth knowing that everyone has a bony bump at the lower back of the skull called the external occipital protuberance. In some people, this ridge is barely noticeable. In others, it’s prominent enough to feel alarming when they discover it for the first time. This is normal anatomy, not a growth.
In some cases, this bony bump can become exaggerated into what’s called an occipital spur. As the protuberance grows larger, it stretches the tissue covering the bone and becomes tender, especially when lying on your back. People with this variation often describe a hard, non-moving bump right at the base of the skull that aches with pressure. No treatment is needed unless the tenderness interferes with sleep or daily comfort.
Cysts: The Most Common Scalp Lump
Pilar cysts (also called trichilemmal cysts) are the single most common type of cyst found on the scalp. They grow from hair follicles, which is why the scalp, with its dense concentration of follicles, is their favorite location. About 10% of the population develops one at some point. They feel like smooth, firm, round lumps that move slightly under the skin when you press on them. Most are painless and grow slowly over months or years.
Epidermoid cysts are the other frequent culprit. These form when skin cells get trapped beneath the surface and create a sac filled with a thick, cheese-like material. They feel similar to pilar cysts but sometimes have a tiny dark dot at the center where the pore opening is blocked. Both types are benign. About 3% of pilar cysts can develop into a more aggressive growth called a proliferating trichilemmal tumor, but this is uncommon, and your doctor can identify concerning changes during an exam.
Cysts occasionally become infected, which makes them red, swollen, and painful. An infected cyst can double in size within days. If you notice sudden tenderness, warmth, or drainage from a previously painless lump, that’s a sign of infection rather than a change in the cyst itself.
Lipomas: Soft and Squishy
Lipomas are slow-growing lumps made of fat cells. They sit just beneath the skin and feel distinctly soft and doughy compared to the firmer texture of a cyst. One classic feature is the “slippage sign,” where the lump seems to slide away from your fingers when you try to press on it. Lipomas are painless, movable, and don’t change the skin above them. They can appear anywhere on the body but favor areas with more fatty tissue, including the back of the head and neck. Once a lipoma reaches its final size, it typically stays put without growing further.
Swollen Lymph Nodes
A pair of small lymph nodes sit right at the base of the skull on either side. These are your occipital lymph nodes, and they swell in response to infections or inflammation in the scalp, the back of the neck, or sometimes the whole body. When enlarged, they feel like firm, tender, pea-sized or marble-sized bumps that may appear on one or both sides.
The most common triggers are local infections: a bacterial skin infection on the scalp, head lice, an infected scratch, or even a flare of scalp psoriasis that’s become secondarily infected. Cat scratch disease can cause occipital lymph node swelling if the scratch happened on the scalp or back of the neck. Systemic infections like mononucleosis (caused by Epstein-Barr virus) can also enlarge lymph nodes throughout the body, including these.
Swollen lymph nodes from infection typically shrink back to normal within two to four weeks once the underlying cause resolves. A lymph node that keeps growing, feels rubbery or hard, is fixed in place, or persists for more than a month without an obvious infection warrants a closer look.
Lumps After a Head Injury
If you bumped your head and now have a lump, you’re likely dealing with a hematoma, which is a collection of blood and fluid beneath the scalp. These lumps can feel surprisingly large because the scalp has a rich blood supply and swells easily. A “goose egg” bump from minor trauma is painful, soft or spongy, and often bruised.
Most minor scalp hematomas heal within about two weeks. If the lump is small, the body gradually reabsorbs the trapped blood on its own, though this process can occasionally take a few months for larger collections. A lump from trauma that gets worse over time rather than better, or one accompanied by headache, confusion, nausea, or vision changes, needs immediate medical evaluation.
Inflammatory Scalp Conditions
Certain chronic skin conditions create painful bumps specifically on the back of the scalp. Folliculitis, an infection or inflammation of hair follicles, produces tender, pimple-like bumps that may cluster together. A more persistent form called acne keloidalis nuchae creates firm, raised bumps along the back of the scalp and neckline, particularly in men with coarse or curly hair. These bumps can become quite hard over time as scar tissue builds up.
A related condition called tufted hair folliculitis tends to favor the back and sides of the scalp. It causes pain, itching, swelling, and slow hair loss in the affected area. Multiple hairs may appear to emerge from a single follicle opening, giving the characteristic “tufted” appearance. These inflammatory conditions don’t resolve on their own and benefit from treatment to prevent scarring and further hair loss.
When a Lump Needs Medical Attention
The features that raise concern are fairly consistent regardless of where a lump appears. According to guidelines from the American Academy of Family Physicians, any soft tissue mass that is 5 centimeters or larger (about the size of a golf ball), feels fixed to deeper structures rather than movable, grows rapidly, or appears suddenly without explanation should be evaluated further. Imaging with ultrasound is often the first step, since it can clarify whether a lump is solid or fluid-filled and how deep it extends. For pilar cysts and other clearly benign lumps, imaging is usually unnecessary.
Other signs worth getting checked include a lump that changes in texture or appearance over weeks, skin breakdown or an open sore over the lump that doesn’t heal within about two months, or persistent pain that worsens rather than improves. A hard lump that’s anchored in place and doesn’t slide under the skin is more concerning than one that moves freely.
For most people, the lump on the back of the head turns out to be a cyst, a lipoma, a swollen lymph node responding to a minor infection, or the bony ridge of the skull itself. Knowing what each type feels like can save you a lot of worry while still helping you recognize the handful of features that deserve a professional evaluation.