Epidermoid Cyst: This is a common, benign cyst that can occur on the scalp, often presenting as a firm, mobile, and sometimes tender bump. It forms from the abnormal growth of skin cells and can become inflamed or infected.

Pilar Cyst: Similar to epidermoid cysts, pilar cysts are benign growths that occur on the scalp, often running in families. They are usually firm and can be tender.
Sebaceous Cyst: These cysts are also benign and occur when the sebaceous gland in the skin becomes blocked. They can appear on the scalp and may become inflamed.
Folliculitis: An inflammation of the hair follicles, which can cause bumps on the scalp. It can be caused by bacterial or fungal infections.
Kerion: A severe form of fungal infection of the scalp, leading to a swollen, painful mass.

Malignant Tumor (e.g., Squamous Cell Carcinoma, Basal Cell Carcinoma): Although less common, any new or changing bump on the scalp should be evaluated for the possibility of skin cancer, especially in individuals with risk factors such as prolonged sun exposure.
Metastatic Lesion: Rarely, a bump on the scalp could be a metastasis from a cancer elsewhere in the body. This would be particularly concerning in patients with a known history of cancer.

Dermoid Cyst: A type of cyst that can occur on the scalp, containing skin and sometimes hair, due to the abnormal formation of skin layers during embryonic development.
Trichoepithelioma: A rare, benign tumor of the hair follicle, which can present as a bump on the scalp.
Cylindroma: A rare skin tumor that can appear on the scalp, often as multiple small bumps. It can be benign or malignant.