A bag at the mouth of the ear would be the earnail cavity or the outer opening of the ear canal. Most of the bags at this location are caused by sebaceous cysts or inflammation of the hair follicles. If the sebaceous gland or hair follicle is inflamed and red, it will lead to pain, and continued aggravation may lead to infection, pus, and then possibly breakage and pus. In the early stage when there is no infection and a red, hard mass appears, you can use antibiotic ointment for application, such as Bactrim ointment or ichthyolite ointment. If it becomes soft, it means that the inside of the mass has become pus, then you need to go to the hospital to have the mass cut open and drained, and the pus will heal when it is released. If it recurs, it needs to be removed completely through surgery, otherwise it will recur. It is caused by the blockage of hair follicles due to excessive oil production.