Depressed fingernail caps may be normal, or they may be due to nail fungus disease, or nail malnutrition. 1. Normal phenomenon: If there is a depressed fingernail cap, it may be that the cuticle on the nail is thicker than the cuticle of the skin, which turns into a fingernail, and there may be a depression of the fingernail, the same as a small peeling of the skin. It does not mean the appearance of other diseases. 2. Nail fungal disease: the cause of its occurrence is mainly due to the nail plate infected with fungi, due to infectious diseases, due to fungal reproduction and destruction, there will be nail deformation, may be manifested in the nail plate depression, become brittle, buckling, loss of luster and other clinical symptoms. 3. Nail dystrophy: its occurrence may be associated with trauma, and chemical agent stimulation, nail dystrophy performance and nail fungal disease performance is more similar, but nail dystrophy, no fungal infection, is the mother of the nail is damaged, the nail growth is poor, and may be manifested in the case of nail depression. If you have a sunken fingernail, it is recommended that you go to the hospital to get a clear explanation of the cause and follow the doctor’s instructions to avoid delaying your condition.