Sebaceous cyst: A common, benign lump that forms due to a blocked oil gland in the skin. It is often movable, firm, and may become inflamed or infected.

Epidermoid cyst: Similar to a sebaceous cyst but typically filled with a cheesy material and may have a central punctum.
Lipoma: A benign tumor composed of fat tissue, which can occur on the scalp and is usually soft and movable.
Folliculitis or furuncle: An inflammation of the hair follicle, which can present as a lump and may be tender or infected.
Keloid or hypertrophic scar: A raised, thickened area of skin that can occur after injury or surgery, more common in individuals prone to keloid formation.

Malignant tumor (e.g., squamous cell carcinoma, basal cell carcinoma, melanoma): Although less common, these can present as a lump on the scalp and are critical to diagnose early due to their potential for metastasis and high mortality if left untreated.
Metastatic lesion: A lump on the scalp could be a metastasis from a cancer elsewhere in the body, which would significantly alter management and prognosis.
Infectious processes (e.g., abscess, osteomyelitis): Especially in immunocompromised patients, these can present as a lump and require urgent treatment to prevent serious complications.

Dermatofibroma: A benign growth that can appear as a firm lump, often following minor injury, and is more common in women.
Cylindroma: A rare, benign tumor that can occur on the scalp, often multiple, and can be associated with genetic syndromes.
Trichoepithelioma: A rare, benign tumor of hair follicle origin, which can present as a lump on the scalp.
Langerhans cell histiocytosis: A rare disorder in which the body accumulates too many immature Langerhans cells, leading to lesions that can appear on the scalp among other places.