Gray nail is a nail fungal disease, a disease caused by various fungi that infect the nail plate and/or subnail tissues. Nail fungal disease with blackened nails is usually the result of an aggravation of the condition, which develops into a total nail-destroying nail fungal disease. When gray nails are left untreated or improperly treated, it can lead to an aggravation of the condition. The nail plate becomes thickened, brittle, and laminated, which leads to the nail plate becoming hollowed out in the middle layer, separating from the nail bed, leaving the nail plate incomplete, and even blackening of the nail. Nail fungal disease according to the fungus invades the nail part and the degree of different, can be divided into: white superficial type, distal lateral subnail type, proximal subnail type, total nail destruction type, total nail destruction type is the final result of the development of each type of nail fungal disease. The manifestation is that the whole nail plate is destroyed, thickened, gray-yellow, black-brown, the nail plate is partially or completely detached, and the surface of the nail bed is left with a rough keratinized accumulation. When nail fungal disease nails become black, it is recommended to go to the hospital as soon as possible, under the guidance of the doctor for targeted treatment.