Flat nails, also known as concave nails, ingrown nails, and spoon-shaped nails, can present as thinning nails that are sunken in the center and raised around the periphery, resembling a spoon. Flat nails cause the surface of the nail plate to become rough and thin, with the center of the nail sunken down and the surrounding area thickened and raised, creating a spoon-like condition, and the depression can be painful if it is too severe. Flat nails can be seen in some systemic diseases, such as iron deficiency anemia, hyperthyroidism or hypothyroidism, and can also be caused by fungal infections, trauma, etc., and need to be treated according to the original cause of the disease, and in severe cases, can be treated by nail extraction. The appearance of flat nails need to consult a doctor in time to clarify the cause of the disease.