The scalp is an intricate area of skin densely packed with hair follicles, oil glands, and blood vessels, making it highly susceptible to various common growths and irritations. This environment is prone to blockages, inflammation, and small masses. Bumps can stem from surface-level issues involving hair structures or from deeper masses forming beneath the skin.
Bumps Related to Hair Follicles and Skin Surface
The most frequent causes of small scalp bumps involve the hair follicles and the surrounding skin layers, often presenting with redness or pus. A common issue is scalp folliculitis, which is the inflammation or infection of the hair follicles, often caused by bacteria or fungi. This condition appears as small, red, pus-filled bumps that resemble acne pustules scattered across the scalp and can sometimes feel tender or sore. Folliculitis typically results from damage to the follicle, perhaps from shaving, heavy hair products, or excessive sweating, allowing microbes to enter and cause infection.
Another prevalent surface condition is seborrheic dermatitis, known as dandruff in its milder form, which can create irritated bumps. This condition is characterized by red, itchy patches covered with greasy, yellowish scales or flakes. The cause is often linked to an overgrowth of Malassezia yeast, which feeds on the oils secreted by the sebaceous glands on the scalp. In infants, this is commonly referred to as cradle cap.
Bumps can also arise from contact dermatitis, which is a localized skin reaction to a specific substance. This allergy or irritation often develops after direct contact with ingredients in hair dyes, shampoos, or other styling products. Contact dermatitis presents as itchy, scaly, and red patches, and in acute cases, it can lead to swelling and sometimes even oozing bumps.
Lumps Beneath the Skin
Some scalp bumps originate deeper, forming masses beneath the skin layer that feel distinct from mere surface inflammation. The most common type of subcutaneous lump on the scalp is the pilar cyst, also known as a trichilemmal cyst. These are benign, slow-growing, firm, and smooth lumps that develop from the cells of the hair root sheath. Pilar cysts are filled with keratin, a protein found in hair and skin cells, and are highly prevalent on the scalp, often appearing as multiple nodules.
A related growth is the epidermoid cyst, which forms when surface skin cells become trapped beneath the skin and create a sac filled with keratin. While epidermoid cysts can occur on the scalp, pilar cysts are significantly more common in this location. Both cyst types usually cause no symptoms unless they become irritated or infected, at which point they may become red, swollen, and painful.
Lipomas are another type of lump that can appear under the scalp, though they are less common there than cysts. These are soft, fatty, non-cancerous tumors that develop between the skin and the underlying muscle. Unlike the firm, sometimes hard feel of a pilar cyst, a lipoma typically feels rubbery, is easily movable when pressed, and grows slowly. These deeper lumps are generally harmless and rarely require removal unless they are bothersome or the diagnosis is uncertain.
Acute Causes and Infections
Bumps can also develop suddenly from external events or rapidly progressing, deep infections. A hematoma is a bump caused by trauma, such as hitting the head, leading to bleeding under the skin. This lump is essentially a collection of blood that swells quickly following the injury and is often accompanied by bruising and pain. Hematomas typically resolve on their own as the body reabsorbs the blood over several days or weeks.
More severe than simple folliculitis are acute, deep-seated infections like boils, also called furuncles, which are large, painful, pus-filled lumps. A boil develops when a hair follicle becomes deeply infected, most often by Staphylococcus aureus bacteria. Boils feel warm, look red, and can grow rapidly, sometimes reaching the size of a walnut, and they are usually much more painful than superficial bumps.
When several boils merge together beneath the skin, a larger, deeper infection called a carbuncle forms. Insect bites can also cause a sudden, localized bump due to an inflammatory reaction, presenting as a raised, itchy swelling that appears quickly and is usually transient.
Warning Signs and Medical Evaluation
While many scalp bumps are benign and resolve on their own, certain signs warrant a medical consultation. Any lump that begins to grow rapidly or changes noticeably in shape or color should be evaluated. Persistent pain, tenderness, or a bump that bleeds easily or does not heal are also concerning symptoms that require professional attention.
Signs of a severe or spreading infection, such as fever, chills, a feeling of general unwellness, or a sudden increase in redness and pain around the bump, necessitate immediate medical care. A healthcare provider will typically perform a physical examination and take a medical history to diagnose the cause. For diagnosis, a doctor may recommend imaging, such as an ultrasound, to examine the lump’s structure beneath the skin.
In some cases, a small tissue sample, known as a biopsy, may be taken to rule out more serious conditions. Treatment for these issues can range from simple drainage of a large abscess or cyst to prescription oral or topical medications, such as antibiotics or antifungals. Consulting a specialist, such as a dermatologist, is recommended if the condition is widespread, if symptoms persist after initial self-care, or if the bump is severe or recurrent.