The causes of downward bending of nails include congenital causes such as independent deformities and acquired causes such as iron deficiency, oxygen deficiency and other disease factors. 1. Congenital causes: due to hereditary factors, nails can appear downward curved phenomenon, and there are no other uncomfortable symptoms. 2. Acquired causes: normal toenails of young children can often be seen temporary anti-nail, and physiological iron deficiency has an obvious relationship; located in the plateau, the air oxygen content is low, triggered by local tissue hypoxia and metabolic disorders can occur, the phenomenon of nails downward bending; such as peripheral vascular circulation is poor, iron-deficiency anemia, etc., due to the lack of oxygen in local tissues, which can lead to nails bending downward. It is recommended that people with downward bending nails go to regular hospitals to clarify the cause, and if treatment is needed, standardize the treatment under the guidance of the doctor to avoid delaying the condition.