Depression in the middle of the thumbnail can be caused by trauma, onychomycosis and psoriasis. 1. Trauma: the depression in the middle of the thumb nail may be caused by trauma, if the nail is hit by external objects, collision or chemical erosion caused by external damage, may lead to this symptom. 2. ringworm: hand thumb nail middle depression may be caused by ringworm, usually caused by dermatophyte infection, mostly caused by ringworm infection. The patient’s nail plate will appear cloudy, thickening, separation, uneven surface, hook nail and nail groove inflammation. The patient’s self-conscious symptoms are mild, and there will be pain and bleeding under the nail and other symptoms. 3. Psoriasis: psoriasis can also lead to depression in the middle of the nail of the thumb of the hand, the cause of psoriasis is still unclear, the disease may be caused by genetic and environmental factors. The patient’s nails are “thimble-like” or point-like depression, nail separation, and hyperkeratosis under the nail. There are many reasons for the sunken nails of the thumb, so we suggest that the patient should consult a doctor for examination, clarify the cause of the disease, and cooperate with the doctor for standardized treatment.