Indentation of the nail cover may be caused by onychomycosis, iron deficiency anemia, etc., which need to be further diagnosed by the doctor. 1. Ringworm of the nails: If the nails are infected by fungus, it can lead to indentation of the nail cover, in addition to nail color change, nail debris, thickening and other manifestations. 2. Iron deficiency anemia: It is an anemia that occurs when the body’s iron storage cannot meet the needs of normal red blood cell production, which can lead to dry skin, dry hair, thin and flat nails that are not smooth and easy to chip, or even spoon-shaped nails, resulting in nail depression. It is recommended that people with sunken nails should go to the hospital in time to clarify the cause of the disease and carry out standardized treatment under the guidance of the doctor, so as to avoid aggravation of the disease due to delayed condition.