Finding an unexpected bump or lump on your skull can be a source of immediate concern, yet the majority of these irregularities are harmless variations in anatomy or benign growths. The skull is a complex structure made up of multiple bony plates and covered by several layers of soft tissue. Understanding whether a bump is part of your natural bone structure, a soft tissue mass, or a new growth helps determine the next step. Most skull bumps fall into predictable categories, ranging from lifelong features to common, non-threatening skin lesions.
Normal Anatomical Features and Bony Landmarks
Many perceived bumps are not new growths but permanent parts of your skull’s architecture. These features feel hard and fixed because they are part of the underlying bone. The most prominent example is the External Occipital Protuberance, a firm elevation often felt at the base of the skull in the center back.
Other natural irregularities include the parietal bosses, which are slight outward curves marking the widest points of the skull on either side of the head. Additionally, the lines where the cranial plates fuse, known as sutures, can sometimes be palpable as subtle ridges. For instance, the sagittal suture runs along the top midline of the head, and its bony connection can feel like a slightly raised seam.
Soft Tissue Bumps and Scalp Lumps
If a bump feels soft, rubbery, or movable under the skin, the cause likely lies within the layers of tissue covering the bone, such as the scalp, fat, or muscle. These soft tissue masses are exceedingly common, and the most frequent among them are cysts and lipomas.
A sebaceous cyst, also referred to as a pilar or epidermoid cyst, forms when a hair follicle or oil gland duct becomes blocked, leading to a pocket filled with keratin. These cysts usually grow slowly, feel firm but pliable, and can often be gently moved beneath the surface of the scalp.
A lipoma is another common soft tissue lump, consisting of a benign collection of mature fatty tissue cells. Lipomas typically feel soft and doughy to the touch and are easily pushed around under the skin with light pressure. They are non-cancerous and generally painless unless they grow large enough to press on nerves.
Trauma can also cause a temporary soft tissue lump, such as a hematoma, which is a collection of blood under the skin resulting from a blow to the head, colloquially known as a “goose egg.” This type of swelling resolves naturally as the body reabsorbs the blood.
Infections can also manifest as painful, localized soft bumps on the scalp. Folliculitis involves inflammation of the hair follicles, sometimes leading to small, red, pus-filled pimples. If the infection progresses deeper, a painful abscess can form, feeling warm and tender to the touch. In all soft tissue cases, the key distinguishing feature is that the lump is separate from the hard, underlying skull bone.
New Bone Growths and Underlying Conditions
Bumps that are fixed, hard, and represent a change or growth of the skull bone itself fall into a different category. The most frequent type of new bony lump is an osteoma or exostosis, which is a benign, slow-growing tumor made of dense, compact bone. Osteomas are typically hard, fixed, and painless, and they are not considered cancerous. These growths can occur on the inner or outer surface of the skull and are often discovered incidentally during imaging for other reasons.
A rare group of conditions involves systemic changes to bone structure that may cause localized skull thickening or bumps. For example, Paget’s disease of bone disrupts the body’s normal process of bone recycling, leading to fragile and misshapen bones, and it can sometimes affect the skull. When Paget’s disease involves the skull, the bone can become enlarged, potentially leading to symptoms like hearing loss or headaches due to nerve compression.
While the vast majority of skull bumps are benign, any new, hard, fixed lump requires medical evaluation to confirm its nature. Skull bone cancer is extremely rare, accounting for a very small percentage of all bone tumors. However, a doctor should evaluate any lump that is rapidly increasing in size, causing severe pain, or accompanied by neurological symptoms like vision changes or numbness. Consulting a healthcare professional provides definitive diagnosis and appropriate management, especially when a lump is fixed and cannot be explained by recent trauma.