Pus under the nail cap is generally an infection of the nail site, commonly acute onychomycosis or purulent dactylitis, may also be caused by trauma; need to be targeted treatment under the guidance of a doctor, such as surgical treatment. 1. Trauma: due to local trauma to the nail, the formation of subcutaneous tissue hematoma, or subcutaneous tissue extrusion and necrosis, so the formation of local abscess; need to consider incision and decompression, drainage. 2. Acute onychomycosis: the initial manifestation of local redness and swelling of the nails, a few days later began to pus, the formation of abscesses, fluctuating sense of touch; with the aggravation of the disease, the lesion can also be extended and spread to cause subnail abscesses. Usually, a longitudinal incision is made along the nail groove to drain the pus; for abscesses at the root of the nail, it may be necessary to remove part or even the whole nail. 3. Purulent dactylitis: purulent infection of the subcutaneous tissue of the palm surface of the terminal segment of the finger, after the initial treatment, if there is throbbing pain, swelling increases, indicating that the pressure in the cavity increases, it should be incised immediately to decompress and drain; if the pus cavity is large, it can be done on the opposite side of the mouth, placed in the latex sheet drainage. However, it is not excluded that it is caused by other reasons. Pus under the fingernail cover should be consulted in time, and standardized treatment should be prescribed by doctors; if it is not detected in time, it may lead to complications such as phalangeal necrosis and phalangeal osteomyelitis, etc., which will seriously threaten the physical health of the patients.