The concave center of the thumb cap is not necessarily due to disease, but may be due to physiological factors such as heredity, or considered to be due to psoriasis, trauma and other diseases. 1. Physiological factors: If the nail is congenitally concave and not accompanied by physical symptoms, it is mostly considered to be caused by physiological factors, so there is no need to worry too much. 2. Psoriasis: It may be caused by heredity, environment, immune function disorder and other factors. Patients may have symptoms such as nail thimble-like depression, nail separation, nail turbidity, etc., and some patients may show concave in the middle of the thumb cap. 3. Trauma: If the patient’s thumb is recently hit by external violence, extrusion, etc., it may lead to deformation of the nail cap, and the middle of the thumb cap will be concave. There are many causes of concave thumb cap, we suggest that patients can identify the cause of the disease and cooperate with doctors to take treatment measures.