There are several possibilities: First, it may be that the lymph nodes behind the ear are inflamed. There is a lymph node behind the ear called the postauricular lymph node, which is responsible for the defense around the ear, and as a defense organ, if there is inflammation and germs invade, it can go to block and kill these germs. However, in the process, it may grow itself, that is, it may become swollen and feel painful. The lymph nodes behind the ear are responsible for one part of the ear, and the other part is a bony protrusion behind the ear called the mastoid process, so if there is mastoiditis or otitis media, the lymph nodes behind the ear are likely to grow. Secondly, if there is an infection on this scalp, such as a small boil or a small infection, or even when washing the hair, the head scratches too much, there may be small wounds, which may cause bacterial infection. Therefore, this place is likely to be inflamed, this possibility is the greatest, touching slightly or a little activity, but during the inflammation of the activity is not very good, this possibility is the greatest. Thirdly, the hard bag behind the ear may be a sebaceous cyst. The skin resuscitator secretes fat and sebum, which has a protective effect on the skin by keeping it from drying out too much. After the opening is blocked, sebaceous cysts may appear. So a hard bag behind the ear and also pain, it is best to go to the hospital to see, the doctor will give an accurate diagnosis, so as not to delay the disease.