This is a "sebaceous" cyst on scalp. In fact, a pathologist will call this an epidermoid cyst as its wall is stratified squamous epithelium producing skin which accumulates in its centre. Usually no sebaceous glands are seen in its wall. It occurs most commonly on the scalp, face and back. It may become infected and is best excised under local anaesthesia. Very occasionally an alternative diagnosis is found by the pathologist and histological examination is therefore recommended.