Nails bent downward may be caused by overgrowth of nails, or nail fungus, iron deficiency anemia and other diseases. 1. Nails are too long: if you don’t trim your nails regularly and don’t pay attention to personal hygiene in your normal life, which leads to excessive nail growth, you will be prone to have nails bending downwards, which is a normal physiological phenomenon. 2. Nail fungus: this disease is caused by dermatophyte infection, mostly seen in red trichophyton, trichophyton fungus, candida, etc., but it may also be caused by direct infection of tinea pedis, common susceptibility factors are nail trauma, local blood circulation and so on. Typical symptoms include unevenness of the nail plate, thickening and turbidity of the nail plate, etc. Some patients will have the phenomenon of nails bending downwards. 3. Iron deficiency anemia: This disease is related to the causes of insufficient iron intake, excessive iron demand and imbalance of iron excretion. Common symptoms include pale skin, dizziness, thinning of nails, and even spatulate nails, which can be manifested as nails bending downward. There are also other causes of crooked nails (e.g. yellow nail syndrome). Patients with crooked nails are advised to go to the hospital and undergo a complete examination to determine the cause.