Blood in the nails may be caused by trauma, onychomycosis and onychomycosis. 1. Trauma: Trauma may cause injury to the nails, and the capillaries under the nails may be damaged or ruptured, leading to blood in the nails. 2. Inflammation of the nail: Inflammation of the nail is mostly considered to be caused by minor trauma secondary to bacterial infection, contact with mutagens and other factors, the patient’s periungual tissues will appear red, swollen, hot and painful, and the inflammation may spread to the underside of the nail plate, and the symptom of blood in the nails may appear. 3. Ringworm of the nails: the appearance of ringworm of the nails may be associated with red trichophyton, candida and other dermatophytes infecting the skin, the patient’s nail plate will appear cloudy, thickening, separation, as well as bleeding under the nail, the patient’s nails may appear blood. The causes of blood in the nails are more, it is recommended that patients go to the regular hospital to clarify the cause.