The Normal Anatomy: Mastoid Processes and the Occipital Protuberance
For many, the two prominent bumps felt on either side of the lower back of the head are simply normal anatomical structures called the mastoid processes. These are conical, rounded projections of bone located on the temporal bones, just behind and below each ear. They provide attachment points for several neck muscles, such as the sternocleidomastoid, which is why they are often more noticeable in individuals with a muscular build or less body fat.
Another normal, midline bony feature is the external occipital protuberance, a palpable ridge or bump at the rear-center of the skull. Sometimes referred to as the 'inion,' this central prominence can vary in size among individuals. A more exaggerated version is sometimes called an occipital bun or spur. This can also feel like a bump and is a harmless, congenital variation of the skull's bone growth.
These bony structures are typically symmetrical, hard, and immobile. If the bumps are located precisely in this area and have been present for as long as you can remember, it is highly likely that they are just a part of your normal skull anatomy. They are not cause for concern.
Other Common Causes of Bumps on the Head
While anatomy is the most probable explanation, other conditions can also cause lumps or bumps in the same area. It is important to distinguish these from the normal skull structure, especially if they are new, growing, or accompanied by other symptoms.
Swollen Occipital Lymph Nodes
Small, kidney-bean-shaped glands called occipital lymph nodes are located at the back of the skull. They play a vital role in the body's immune system, filtering out bacteria and other invaders. These nodes can swell in response to a nearby infection, such as:
- Skin infections on the scalp (e.g., from excessive scratching or cuts).
- Head lice infestations.
- Scalp conditions like psoriasis or ringworm.
- An illness affecting the upper body.
Unlike bony protrusions, swollen lymph nodes are typically softer, movable under the skin, and may be tender or painful to the touch. They usually return to their normal size once the underlying infection is cleared.
Cysts and Fatty Growths
Different types of benign (noncancerous) growths can form under the scalp and feel like bumps:
- Pilar cysts: These are keratin-filled sacs that commonly form around hair follicles on the scalp. They are smooth, firm, and slow-growing, though they can sometimes grow large or become painful if they rupture or get infected.
- Lipomas: These are soft, fatty growths that can occur anywhere on the body, including the head and neck. They feel rubbery and can move slightly when pressed. Lipomas are generally painless and harmless.
- Epidermoid cysts: Similar to pilar cysts, these are also keratin-filled but tend to have a small, central opening. They are the most common type of cutaneous cyst and are rarely cancerous.
Less Common but Serious Conditions
In rare cases, bumps on the head can be a symptom of a more serious issue. It is important not to jump to conclusions, as these are far less likely than the more common causes mentioned above.
- Bone Spurs (Osteomas): Benign bony outgrowths can sometimes develop on the skull and facial bones. While many are asymptomatic, larger ones might cause headaches or other issues depending on their location.
- Occipital Neuralgia: This condition involves pain in the upper neck, back of the head, and behind the ears, caused by irritation or damage to the occipital nerves. While it doesn't cause a visible bump, the tenderness can be mistaken for one.
- Tumors: Although extremely rare, a bump could signify a tumor, which can be either benign or cancerous. However, most bumps are not tumors.
Comparison of Common Bump Causes
| Feature | Mastoid Processes | Swollen Lymph Nodes | Pilar Cysts | Lipomas |
|---|---|---|---|---|
| Location | Behind each ear, lower sides of the skull | Often at the hairline, on the scalp, or behind the ears | On the scalp, growing from hair follicles | Under the skin, anywhere on the head |
| Texture | Hard, immovable bony structure | Softer, movable, and sometimes tender | Firm, smooth, and sometimes dense | Soft, rubbery, and easily movable |
| Symmetry | Symmetrical | Can be asymmetrical (one side) | Can be single or multiple | Can be single or multiple |
| Speed of Appearance | Present since birth/development | Appears or swells in response to illness | Slow-growing | Slow-growing |
| Symptoms | None normally; tenderness if pressed hard | Tenderness, pain, and possible fever | Usually painless unless infected or ruptured | Typically painless |
When to Contact a Doctor
While most bumps on the back of the head are benign, it is important to seek medical advice if you experience any concerning symptoms. According to Healthline, a doctor should be consulted if a bump:
- Grows rapidly in size or changes shape.
- Is accompanied by severe or persistent pain.
- Becomes warm to the touch, red, or oozes pus or discharge.
- Is a new lump following a head injury and you experience confusion, dizziness, or vision problems.
For most people, the discovery of symmetrical bumps at the back of the head is simply a newfound awareness of their own anatomy. However, paying attention to the texture, mobility, and any accompanying symptoms is crucial for differentiating a normal finding from a problem that may require medical attention.
Conclusion
The most common reason for feeling two large bumps in your skull on the right and left side of the back of your head is the presence of normal bony features known as the mastoid processes. These and the central external occipital protuberance are part of your innate skull structure and are harmless. However, other potential causes include swollen lymph nodes from infection, or benign growths like cysts and lipomas. By observing the characteristics of the bumps and monitoring for any changes, you can better understand their origin. If the bumps are new, painful, or you have other symptoms, a consultation with a healthcare professional can provide clarity and rule out any underlying medical issues. For reliable, authoritative health information, consider visiting sources like the National Institutes of Health.
