Nails that are concave in the middle can be caused by congenital factors, anemia, and fungal infections. 1. Congenital factors: the depression in the middle of the nail is usually called antinail in clinical practice. Some patients are caused by family genetic factors, but this symptom has no substantial health hazards to the human body, so clinically generally do not need special treatment. 2. Anemia: when the patient is severely anemic, it may lead to abnormal function of the nail matrix cells at the root of the nail, and the structure of the synthetic nail plate is changed, and the middle depression may appear, and the symptoms of anti-nail can appear with severe anemia. 3. Fungal infection: it is a relatively common cause, such as dermatophytes and other pathogenic fungi after infection of the nail plate, it can lead to unevenness, color change, thickening and so on on the nail plate. In summary, if the patient is acquired factors caused by the middle of the nail concave, it is recommended to go to the hospital in time, clear causes, timely treatment.