To see whether the flat nail is mainly from the nail form and causes and other aspects to determine, need to be specifically analyzed. 1. Nail morphology: normal nail morphology generally has a certain physiological curvature, wrapped around the distal skin of the finger, able to grow smoothly on the nail bed, while flat nails are completely flat, or even have reverse physiological curvature, some patients even show a reverse spoon shape or tooth shape. 2. Causes: The appearance of flat nails is related to multiple factors, such as nail malnutrition, special blood diseases, nail extrusion or trauma, etc. These factors will affect the growth of the nail plate and nail bed, resulting in the appearance of abnormal nail plate shape. If the patient’s flat nail symptoms are serious, or the symptoms continue for several days without improvement, should promptly go to the hospital for treatment, under the guidance of the doctor for treatment.