Dorsal carbuncle is a suppurative infection that occurs on the back, which is divided into three phases: early onset, pus formation and ulceration, and the symptoms of each phase are different, as follows: 1. Early stage: the skin of the affected area is red and swollen, with burning and painful sensation, but there is no pus head, the development is relatively rapid, and it can spread to the surrounding skin with clear boundaries. 2. Pus stage: the pus stage can be manifested as localized redness and swelling of the affected area, high protrusion, pain, burning sensation aggravated compared with the early stage, and the surface of the pus has been generated by the feeling of softness when pressed down. Usually, back canker sores will enter the abscess stage in about 7 days, usually not more than half a month. The abscess can be broken on its own or under artificial intervention, and yellowish-white pus will flow out. 3. Ulcer stage: the redness, swelling and pain of the affected area disappears, the burning sensation and systemic symptoms disappear, the pus in the ulcerated area is gradually exhausted, and the mouth begins to close and heal. The back carbuncle should be treated in time.