How is fingernail bend downward to return a responsibility

Antionychia is classified into congenital and acquired. Most antionychia is acquired. There are many causes of this disease, mainly seen in low hemoglobin, hypoxia, vitamin deficiency, hyperthyroidism, rheumatic fever, certain bacterial infections (such as syphilis, fungi, typhoid, etc.) and occupational strong acids and strong bases and oil producers. It is also possible that the nail growth caused by calcium deficiency is abnormal, calcium deficiency should be caused by timely calcium supplementation, usually eat more dairy products, soy products, fresh fruits and vegetables, and more sun exposure.