Finding a bump on your scalp is extremely common. The human scalp is a unique environment, rich in hair follicles, blood vessels, and specialized skin layers. Most scalp bumps are benign, representing harmless conditions ranging from structural growths to temporary reactions. Understanding the origin and characteristics of these lesions helps categorize the most likely causes and determine when a professional evaluation is necessary.
Common Benign Skin Growths
Many scalp bumps are structural formations that develop slowly over time and are not related to active infection or injury. The most frequent of these is the pilar cyst, which accounts for over 90% of all cysts found on the scalp. These growths originate from the outer root sheath of the hair follicle, presenting as firm, smooth, skin-colored nodules beneath the skin’s surface. Pilar cysts are filled with keratin and its breakdown products, a protein component of hair and nails, and are usually painless unless they rupture or become inflamed.
Another common structural growth is the lipoma, a benign tumor composed of mature fat cells. A lipoma on the scalp typically presents as a soft, doughy, and movable subcutaneous nodule. A characteristic sign is the “slippage sign,” where the lump easily moves under slight finger pressure. These growths are generally painless, slow-growing, and do not cause changes to the overlying skin.
A third frequently observed growth, especially in older adults, is seborrheic keratosis. These lesions develop from the proliferation of epidermal cells and have a distinctive, waxy appearance, often described as “stuck-on” to the skin. They vary in color from light tan to dark brown or black and may feel slightly rough or scaly. Though harmless, they can become irritated if constantly rubbed.
Bumps Caused by Inflammation or Infection
Bumps that appear suddenly with pain, heat, or redness are usually the result of inflammation or infection. Folliculitis is a superficial condition caused by the infection of the hair follicle, often triggered by bacteria like Staphylococcus aureus. This results in small, red, pimple-like bumps that may contain pus and can be tender, itchy, or cause a mild burning sensation. Mild cases may resolve on their own, but persistent lesions often require topical or oral treatment.
A more severe, deeper infection of the hair follicle is a furuncle, commonly known as a boil. A furuncle represents a painful, deeper collection of pus and necrotic tissue under the skin, often larger and more intensely inflamed than folliculitis. These lumps feel warm to the touch and typically require medical attention, sometimes involving incision and drainage to alleviate pressure and clear the infection.
Severe acne vulgaris can also manifest on the scalp, presenting as firm, painful nodules or cysts deep beneath the skin. These lesions arise when hair follicles become deeply clogged with oil and dead skin cells, allowing bacteria to multiply and cause intense inflammation. Unlike superficial pimples, these deeper formations are more likely to cause scarring or permanent hair loss in the affected area.
Trauma-Related Bumps and Temporary Causes
Some bumps result from an external event, leading to temporary swelling that resolves as the body heals. The classic “goose egg” that forms rapidly after a direct blow is a hematoma, a collection of clotted blood under the skin. Because the scalp is highly vascular, blood vessels easily rupture upon impact, pooling quickly to form a firm, tender lump. These hematomas are temporary and gradually change color like a bruise, fading over one to two weeks.
Localized inflammation can also be caused by the body’s reaction to irritants, such as an insect bite or sting. The injected venom or saliva triggers an immediate immune response, leading to a small, itchy, and sometimes painful swelling. Similarly, contact dermatitis from an allergic reaction to a hair product can cause localized hives or a patch of bumpy, itchy skin. These temporary reactions are generally characterized by immediate onset and associated itching.
Indicators That Require Medical Consultation
While most scalp bumps are harmless, certain features should prompt a medical consultation. Any bump that exhibits rapid growth, changes significantly in color or shape, or develops irregular borders warrants immediate professional examination. A lesion that bleeds easily, scabs repeatedly, or fails to heal completely within a few weeks is also a concerning sign. These changes may indicate an underlying malignancy or a more aggressive form of growth.
Signs of a spreading or systemic infection also require prompt medical attention. This includes a bump accompanied by severe pain, increasing redness spreading outward, a high fever, or chills. Following a head injury, if the bump is accompanied by neurological symptoms such as persistent headache, confusion, dizziness, or changes in vision, seek emergency care immediately. Only a healthcare professional can perform a proper evaluation, which may involve imaging or a biopsy, to provide an accurate diagnosis and treatment plan.