Finding a lump on the back of your head can cause concern, but most bumps in the occipital region, or the base of the skull, are common and benign. This area contains bone, muscle, skin, and lymph nodes, all of which can develop a lump for different, often harmless, reasons. Understanding the source of the lump is the first step toward peace of mind.
Understanding Normal Skull Anatomy
The most frequent reason for a hard, unmoving bump at the center of the back of the head is the external occipital protuberance (EOP). This bony projection on the occipital bone is present in every human skull. The highest point, sometimes called the inion, functions as the anchor point for the nuchal ligament and several neck muscles.
The size of the EOP varies significantly among individuals, explaining why some people feel a prominent knob while others do not. In some cases, the EOP can be notably enlarged, sometimes classified as an occipital spur or occipital knob. If the bump is firm, has been present since childhood, and is fixed directly to the skull, it is highly likely to be this normal anatomical variation.
Common Benign Soft Tissue Growths
Many lumps that appear beneath the skin but are not part of the bone are benign soft tissue growths that develop slowly over time. These masses are typically painless unless they become irritated or infected. Lipomas and epidermoid cysts represent two of the most common types of these non-cancerous formations found on the scalp.
Lipomas are subcutaneous tumors composed of mature fatty tissue, making them soft and doughy to the touch. They are typically easily movable beneath the skin and grow slowly, often reaching a diameter of less than two inches. Because they are encapsulated, they are almost always harmless and rarely require treatment unless they cause discomfort or cosmetic concern.
Epidermoid cysts, which are often mistakenly called sebaceous cysts, originate from the hair follicle and are filled with keratin, a protein found in skin, hair, and nails. These cysts present as firm, smooth, and moveable nodules that are fixed to the skin surface. If ruptured or infected, the cyst can become tender, red, and may exude a thick, yellowish material that sometimes has a foul odor.
Bumps Resulting from Injury or Infection
Bumps that appear suddenly or are accompanied by tenderness, warmth, or pain are generally the result of trauma or infection. A direct blow to the back of the head often causes a contusion, or a “goose egg,” which is a hematoma formed by bleeding under the scalp. The scalp is highly vascular, so even minor trauma can lead to noticeable swelling as blood pools between the skin and the skull.
Infections on the scalp can cause the occipital lymph nodes to swell, a condition known as occipital lymphadenopathy. These small, oval-shaped nodes are positioned at the base of the skull and filter fluid from the posterior scalp and neck region. They become enlarged and tender as they fill with immune cells fighting an infection, such as a localized skin infection, folliculitis, or even a fungal infection like ringworm.
Localized skin infections, including abscesses and folliculitis, are pus-filled lumps that are typically painful, warm, and red to the touch. Folliculitis occurs when hair follicles become inflamed, while an abscess is a larger, deeper pocket of infection in the tissue. These inflammatory conditions cause a rapid, acute swelling that is distinct from the slow, chronic growth of a cyst or lipoma.
Identifying Signs for Medical Concern
While most lumps on the back of the head are benign, certain signs suggest the need for a prompt medical evaluation. Any lump that begins to grow rapidly over weeks or months should be examined by a healthcare provider. A bump that feels hard, fixed, or immobile also warrants a professional opinion.
If the lump is accompanied by systemic symptoms, such as fever, chills, or significant pain, this could indicate a serious infection or other condition. Following a head injury, seek immediate care if you experience neurological changes, which are red flags for internal bleeding or a concussion.
Seek Immediate Care If You Experience:
- Confusion
- Persistent or worsening headache
- Vomiting
- Loss of consciousness
- Weakness on one side of the body