Big toe with horizontal lines refers to big toe nails with horizontal lines, there are many reasons, physiological such as long-term extrusion, pathological such as nail fungal disease, anemia and other factors. 1. Long-term extrusion: engaging in physical labor or sports is one of the common physiological causes of nail deformation, in the process, the nails may be subjected to long-term extrusion, which leads to nail deformation and thus lead to big toe nail horizontal lines. If you want to avoid this situation, then you have to pay attention to the combination of work and rest, wear comfortable shoes and socks, pay attention to the protection of the toes. 2. Nail fungal disease: toes infected with fungi, nails will appear cloudy, thickening, separation and unevenness and other symptoms, some of the patients may appear white, yellow and dirty color nail plate lines or longitudinal stripes, which is formed in the skin with ringworm infection and damage to the nail plate. 3. Anemia: When anemia occurs in the body, the lack of nutrient supply to the nails can also lead to nail lesions, which in turn can lead to the appearance of horizontal lines on the big toe nails. There are other reasons that can lead to big toe nails with horizontal lines (such as lack of vitamins, etc.), in order to find out the cause of the disease as soon as possible, it is recommended to go to the hospital in a timely manner to find out the cause of the symptoms and then targeted treatment, avoid self-medication.