Pus flowing behind the ear is considered to be secondary infection of sebaceous cysts that occur under the skin behind the ear, because the face is a rich area of sweat gland secretion, and poor local hygiene can easily lead to blockage of sweat glands and secondary obstruction to form sebaceous cysts, which initially appear as localized masses and gradually evolve into secondary infection, manifesting as pus, and the patient may also experience pain and fever. If the skin on the surface of the lesion breaks down, it may manifest itself as pus or even pus and blood-like fluid oozing out. In this case, surgery to enlarge the incision and drainage should be chosen in a timely manner, and after the surgery, drug changes should be performed intermittently, and re-suturing can be chosen if the wound is well healed and the granulation tissue is fresh. Local hygiene should be observed and underlying diseases such as diabetes should be actively controlled.