A bulge behind the ear can be caused by lipoma, sebaceous cyst, or boils. 1. Lipoma: This disease is a tumor of fat-like tissue and is a benign tumor of soft tissue. It is usually a painless lump of small size. If the bulge behind the ear has a clear boundary, soft texture, elasticity, and slight movement when pushed by the finger, it cannot be excluded as a lipoma. 2. Sebaceous cysts: due to the obstruction of sebaceous gland ducts, the cysts formed by the accumulation of gland contents are mostly round, moderately hard or elastic, higher than the skin surface, with smooth surface, the top of the cyst is adhered to the skin when pushed and the bottom of it is not adhered to subcutaneous tissues without any fluctuating sensation, and there is a small pigmentation point in the center of the protruding object, and there is powdery material overflow when squeezed, and there is redness, swelling and heat pain when secondary infection occurs. 3. Behind-the-ear boils: boils are more commonly caused by bacterial infections such as Staphylococcus aureus, due to bacterial infections of the local skin, so that the hair follicle localized acute purulent lesions and the formation of boils. If the raised bulge behind the ear is red, swollen and painful to the touch, it may be a boil. In addition, a raised bulge behind the ear may also refer to a mastoid, etc. It is recommended to consult a doctor promptly for an accurate diagnosis.