Thickening and hardening of nails is related to age factor, thick nail syndrome, gray nails or other factors. 1. Age factor: With age, the body’s metabolism slows down and keratin builds up in the nail area, which may lead to thickening and hardening of nails, and generally does not require special treatment. 2. Thick nails: Thick nails are considered to be related to heredity. Influenced by genetic factors, babies may have thickened nails from birth or a few months after birth. 3. Gray Nail: Gray Nail is caused by fungal infection. Fungus invades the nail plate and subnail tissues, resulting in changes in the nature and texture of nails, which may become thicker, harder and yellowish. 4. Other factors: nails are subject to external forces, such as extrusion damage, resulting in thickening and hardening. Lichen planus, hairy erythema, etc., are also the main causes of thickening and hardening of nails. To sum up, there are many possibilities for thickening and hardening of nails, it is recommended to go to the hospital to clarify the cause and standardize the treatment under the guidance of the doctor.