The protruding bone behind the ear, clinically referred to as the mastoid process, is a component of the temporal bone, and clinically the mastoid process is left and right, and is essentially symmetrical in size. In males, the mastoid process is more prominent than in females because of the attachment of the sternocleidomastoid muscle to the nipple, which is stronger in males, resulting in a more pronounced protrusion of the mastoid process to facilitate the attachment of the muscle. There are also lymph nodes in the mastoid area on the surface of the mastoid process, and the deeper part of the mastoid process is mainly composed of the mastoid airspace, which communicates with the middle ear through the tympanic sinus. Clinically, the mastoid process is mainly divided into pneumatized, sclerotic, platysma barrier, and mixed types. If the mastoid bone is too hyperplastic an osteoma can be formed, which is often the case in clinical practice. In conclusion, a bony protrusion behind the ear is called a mastoid, which is a normal structure of the human body, and patients should not be worried or afraid if they touch this mastoid bone behind the ear.