Finding a bump on the head is very common. Some lumps or bumps occur on the skin, under the skin, or on the bone. There are a wide variety of causes of these bumps.

In addition, each human skull has a natural bump on the back of the head. This bump, called an inion, marks the bottom of the skull where it attaches to the neck muscle.

There are many reasons why you could develop a bump on the back of your head. Most are harmless. In rare cases, however, a lump on the head could indicate a more serious problem. If you notice changes with the bump on your head, if it’s bleeding or is painful, your doctor.

1. Head injury

If you hit your head on a hard object, you may experience a head injury. If a bump on your head appears after a head injury, it’s a sign your head was hurt and the body is trying to heal itself.

Some scenarios that can result in head injuries are:

Head injuries can result in a scalp hematoma, or blood clot. If you experience a small head injury and a lump develops on your head, the developed hematoma is a sign that there is minor bleeding under the skin. These bumps typically go away after a few days.

More traumatic head injuries can cause larger bumps, or even bleeding on the brain (intracranial, epidural, and subdural hematomas).

If you experience a head injury — especially one that causes you to lose consciousness — visit your doctor to ensure you’re not bleeding internally.

2. Ingrown hair

If you shave your head, you may get ingrown hairs. This occurs when a shaved hair grows into the skin, rather than through it, causing a small, red, solid bump. Sometimes an ingrown hair can become infected and turn into a pus-filled bump.

Ingrown hairs are typically harmless and often correct themselves as the hair grows out. You can prevent ingrown hairs by letting your hair grow.

3. Folliculitis

Folliculitis is the inflammation or infection of a hair follicle. Bacterial and fungal infections can cause folliculitis. These bumps can be red or look like whitehead pimples.

This condition is also called:

In addition to bumps on the head, people with folliculitis on the scalp may also experience itching and soreness. If left untreated, the infections could turn into open sores.

Treatment for folliculitis includes:

  • not wearing hats
  • not shaving
  • avoiding swimming pools and hot tubs
  • use of prescription antibiotic creams, pills, or shampoos

In rare, extreme cases, laser hair removal or surgery may be necessary.

4. Seborrheic keratoses

Seborrheic keratoses are noncancerous skin growths that look and feel like warts. They typically appear on the head and neck of older adults. These bumps are usually harmless, even though they may look similar to skin cancer. For this reason, they are rarely treated. If your doctor is worried the seborrheic keratoses will become skin cancer, they may remove it using cryotherapy or electrosurgery.

5. Epidermal cyst

Epidermoid cysts are small, hard bumps that grow under the skin. These slow-growing cysts frequently occur on the scalp and face. They do not cause pain, and are skin-colored or yellow.

A buildup of keratin below the skin is often the cause of epidermoid cysts. They are very rarely cancerous. Sometimes these cysts will go away on their own. They usually aren’t treated or removed unless they become infected and painful.

6. Pilar cyst

Pilar cysts are another type of slow-growing, benign cyst that develop on the skin. Pilar cysts most frequently occur on the scalp. They can range in size, but are almost always smooth, dome-shaped and skin-colored.

These cysts are not painful to touch. They are not typically treated or removed unless they become infected, or for cosmetic reasons.

7. Lipoma

A lipoma is a noncancerous tumor. They are the most common soft tissue tumor found in adults, but are rarely seen on the head. More commonly, they occur on the neck and shoulders.

Lipomas are located under the skin. They often feel soft or rubbery and move slightly when touched. They are not painful and are harmless. There is typically no need to treat lipomas. If the tumor grows, however, your doctor may recommend surgery to remove it.

8. Pilomatrixoma

A pilomatrixoma is a noncancerous skin tumor. It feels hard to the touch because it occurs after cells calcify under the skin. These tumors commonly occur on the face, head, and neck. Typically, only one lump forms and it grows slowly over time. These bumps normally don’t hurt.

Pilomatrixoma can be found in children and adults. There is a small chance a pilomatrixoma can turn into cancer. For this reason, treatment is typically avoided. If the pilomatrixoma becomes infected, your doctor may remove it surgically.

9. Basal cell carcinoma

Basal cell carcinomas (BCCs) are cancerous tumors that develop in the deepest layer of the skin. They can be red or pink and look like bumps, sores, or scars. BCCs often develop after repeated, intense sun exposure.

This type of skin cancer typically does not spread. However, it should still be taken seriously. Mohs surgery is the most effective form of treatment.

10. Exostosis

Exostosis is the growth of bone on top of existing bone. These bony growths often first appear in childhood. They can occur on any bone, but rarely occur on the head. An X-ray can reveal if the bump on your head is an exostosis. Treatment for bony growths depend on what complications, if any, arise. In serious cases, surgery may be required.

There are many conditions that can cause a bump on the back of the head. Treatment varies based on the cause. Most bumps on the head are harmless.

If you’re unsure what’s caused the lump on your head, inform your doctor and watch the lump closely. If it changes or any of the following occur, call your doctor immediately:

  • bleeding
  • increased pain
  • growth
  • transformation into an open sore