The depression in the middle of the nail may be related to psoriasis nail, lichen planus, onychomycosis and nail trauma. 1. Psoriasis nail: it is a kind of lesion caused by psoriasis involving the nails, which is manifested as thimble-like depression on the surface of nails in the clinic. 2. Nail lichen planus: a chronic inflammatory disease of unknown origin, mainly manifested as unevenness of the nail plate, thickening of the nail plate and roughness of the nail surface. 3. Nail fungus: it is a kind of disease caused by nails infected with fungus through various reasons, because the fungus will affect the nail plate and the nail bed, so it will lead to nail deformation, thickening, discoloration and so on in the clinic. 4. Nail trauma: it will affect the nail bed and the normal growth of the nail plate, there may be nail depression, horizontal lines and other deformation phenomena. As there are many factors affecting the nail, the specific situation needs to be analyzed after the doctor’s consultation.