Grey nails are a fungal disease caused by fungal infection of the nail plate as well as the nail tissue underneath. Grey nails become black for the following common reasons: 1. Inadequate nutrition: Grey nail patients are unable to get adequate nutritional support for their nails due to invasion and damage by nail fungus, and the longer the time, the deeper the color of the nail area will be, eventually becoming black; 2. Aggravation: If the grey nail is not treated properly or not treated leading to The nail condition will change as well, mainly because the color becomes black, accompanied by nail plate thickening, brittle, lamellar, badly broken, buckling, nail plate middle hollow, nail edge uneven, nail plate and nail bed separation, so that the nail plate is incomplete, nail atrophy deformation, and even missing or fallen off; 3, bad habits: some patients wear non-breathable shoes and socks for a long time, long time not to wash feet The actual nail is often in a warm and humid environment, which can also lead to the color of gray nails becoming darker and darker. The blackened nails may affect the normal life and social life of the patient, so you need to seek medical advice and take the correct treatment to control the condition as soon as possible.