Gray nails may be caused by nail malnutrition and onychomycosis. 1. Nail malnutrition: If the diet is not balanced, lack of certain nutrients and lead to nail malnutrition, the phenomenon of dark nails may occur. 2. Ringworm: caused by fungal infection, the main symptom is that the nail plate color will change, will become cloudy, and will be thickened, there will also be the phenomenon of warping, the surface of the nail is uneven. It is recommended to actively go to the regular hospital for relevant examinations, a clear diagnosis, and then according to the situation under the guidance of the doctor to deal with, so as not to delay the condition.