A bump on your head is almost always harmless. The most common causes are cysts, minor injuries, and small fatty growths, all of which resolve on their own or with simple treatment. That said, the feel, location, and behavior of the bump can tell you a lot about what’s going on and whether it deserves attention.
Cysts: The Most Common Scalp Bump
If you’ve found a smooth, round, moveable lump under the skin of your scalp, there’s a good chance it’s a pilar cyst. These grow from hair follicles and are filled with keratin, the same protein that makes up your hair and nails. They affect roughly 10% of the population, making them one of the most common lumps people discover on their heads. Pilar cysts are flesh-colored, painless, and grow slowly, though they can eventually reach the size of a baseball if left alone for years.
Sebaceous cysts look similar but have a key difference: they develop from oil-producing glands rather than hair follicles and tend to have a tiny opening on top. If you squeeze one (which isn’t recommended), it oozes an oily substance called sebum. Sebaceous cysts can appear almost anywhere on the body, but the scalp is a favorite spot. Both types of cyst are benign. A doctor can remove either one with a quick in-office procedure if it bothers you or keeps getting bigger.
Bumps From Injury
A bump that appeared after you hit your head is a collection of blood and fluid trapped under the scalp, commonly called a “goose egg.” The scalp has an unusually rich blood supply, which is why even a minor knock can produce a lump that looks alarmingly large. This is normal. The swelling typically takes about a week to go away on its own as your body reabsorbs the fluid.
Ice wrapped in a cloth and applied for 15 to 20 minutes can reduce swelling in the first day or two. What matters more than the size of the bump is how you feel afterward. The CDC lists specific danger signs that warrant an immediate trip to the emergency room:
- A headache that keeps getting worse and won’t go away
- Repeated vomiting
- Slurred speech, confusion, or unusual behavior
- One pupil visibly larger than the other
- Weakness, numbness, seizures, or loss of coordination
- Extreme drowsiness or inability to wake up
These signs can indicate a blood clot forming between the brain and skull, which is rare but serious. Symptoms don’t always show up right away. Some appear hours or even a day later, so it’s worth paying attention to how you feel in the 24 to 48 hours after any head injury.
Monitoring a Child’s Head Bump
Kids bump their heads constantly, and the vast majority of those bumps are nothing to worry about. Watch your child closely in the first hour after the injury for the danger signs listed above, plus two additional red flags specific to young children: inconsolable crying that won’t stop, and refusal to eat or nurse.
In the days following a bump, let your child sleep normally. There’s no need to wake them repeatedly through the night, and you shouldn’t keep them lying in a dark room all day either. Limit screen time for the first one to two days, and encourage light activity like short walks. Hold off on sports, bike riding, or anything with a risk of another impact until a healthcare provider clears them.
Hard, Bony Bumps
If the bump feels rock-hard and doesn’t move when you press on it, you may be feeling an osteoma. These are benign bony growths that develop directly on the skull. They grow extremely slowly and almost never cause symptoms. Most people discover them by chance while washing their hair or scratching their head. Osteomas don’t require treatment unless they’re large enough to press on nearby structures, which is uncommon on the top or sides of the skull.
Inflamed or Painful Bumps
Not all scalp bumps sit quietly under the skin. Some are red, tender, or filled with pus, which usually points to an infection or inflammation at the hair follicle. Scalp folliculitis produces itchy or painful little pustules, often from bacteria getting into a follicle through a scratch, tight hat, or heavy sweating. It doesn’t cause hair loss and typically clears up with proper hygiene, though stubborn cases may need a course of antibiotics.
More serious inflammatory conditions can create firm, raised nodules or even large cyst-like swellings with crusting and hair loss in the affected area. These are less common but tend to need medical treatment to prevent scarring.
Fatty Growths (Lipomas)
A lipoma is a soft, rubbery lump made of fat cells that sits just under the skin. When you press on it, it moves easily and doesn’t hurt. Lipomas can appear anywhere on the body, including the scalp. They’re benign, grow slowly, and rarely need treatment unless they become large or uncomfortable. Most stay well under 5 cm (about 2 inches) in diameter.
When a Bump Could Be Something Serious
Skin cancer can develop on the scalp, particularly in areas with thinning hair or regular sun exposure. Squamous cell carcinoma, one of the more common types, can appear as a firm nodule that may be pink, red, brown, or the same color as your surrounding skin. It can also look like a flat sore with a scaly crust that won’t heal. The key warning sign is persistence: any sore or scab on your scalp that hasn’t healed within about two months deserves a professional evaluation.
For any soft tissue lump, doctors generally recommend further workup if the mass is 5 cm or larger, grows rapidly, sits deep beneath the skin, or appeared suddenly without an obvious explanation. These features don’t automatically mean cancer, but they do raise the odds enough that imaging, usually an MRI, is warranted. If there’s concern about a malignant growth, a specialist will perform a biopsy rather than a general practitioner, to avoid complications at the biopsy site.
How to Tell What Your Bump Is
You can narrow things down with a few simple observations:
- Soft and moveable: likely a cyst or lipoma
- Hard and fixed to the bone: likely an osteoma
- Appeared after an impact: likely a hematoma (goose egg)
- Red, tender, or has pus: likely folliculitis or an infected cyst
- Scaly, crusty, or won’t heal: worth a skin check for possible cancer
Most head bumps fall squarely into the harmless category. A cyst or lipoma that’s been sitting there unchanged for months or years is almost certainly benign. What should prompt a visit to your doctor is any bump that grows noticeably over weeks, changes in appearance, bleeds or ulcerates, or causes new symptoms like headaches or vision changes.