Gray nails may be caused by trauma, onychomycosis and other diseases. 1. trauma: if the nails have been hit by the outside world, injury and extrusion, it may lead to the rupture of the capillaries under the nails, resulting in local bruising, which leads to the appearance of gray nails. 2. ringworm of the nail: ringworm of the nail is a disease caused by dermatophytes invading the nail plate, the cause of which is mostly related to the infection of dermatophytes such as Trichophyton rubrum, Candida, and Trichophyton mustelii, etc. The nail plate of the patient will appear cloudy, thickened, uneven and so on, and the nail plate’s color will also be changed, which manifests itself as white, yellow, grey, and stained color, and so on. The cause of gray nails is not unique, it is recommended that patients seek medical examination to clarify the cause of the disease.