There are several causes for a sunken thumb nail. The most common cause is a fungal infection, which often leads to a sunken nail at the front or the entire nail. If the diagnosis is clear, anti-fungal treatment can be administered. There are also patients with calcium deficiency, which is often associated with other systemic problems, such as delayed bone development and mental weakness, and can be diagnosed with a timely blood calcium test. Some patients may have gastrointestinal and digestive tract symptoms, such as weakness and pallor. The severity of anemia can be determined through routine blood tests, and active blood transfusion treatment can be given to find the cause of anemia.