Sudden redness and swelling of the thumb may be due to the development of onychomycosis, which occurs when bacterial infection occurs in the nail grooves on both sides of the nail bed after cutting the nails too short, pulling out barbs, or not paying attention to hygiene on the hands. The patient’s thumb suddenly becomes red, swollen and hot, and if a localized abscess is present, the pain may be a more intense throbbing pain. Treatment requires incision of the swollen area, extrusion and drainage of pus, aseptic bandage, severe throbbing pain can be relieved, or topical application of Revernolol, which is often referred to as yellow drops, given anti-inflammatory symptomatic treatment, 3-7 days can be cured.