White horizontal lines on the toenails are usually considered to be caused by trauma, but may also be caused by nutritional deficiencies, which can be clearly diagnosed after completing a micronutrient test and can be relieved by supplementation. In addition, you need to consider the fungal infection caused by the gray nail white horizontal lines, then you need to go through regular treatment to relieve the symptoms: 1, trauma: toe nails by hard objects bumped may lead to white horizontal lines, this situation does not require special treatment, a period of time will be self-healing. If the bump is serious, you need to go to the hospital for bandaging and other treatment; 2, lack of nutrients: the usual diet is not balanced, the intake of nutrients, such as calcium, vitamin D, etc.. In addition, hypoparathyroidism can also affect calcium metabolism, resulting in calcium deficiency. Therefore, you should pay attention to a balanced diet in your daily life to ensure adequate nutritional intake; 3. Grey nails: Grey nails, also known as onychomycosis, are mainly caused by fungi such as dermatophytes, yeasts, and non-dermatophytic mycobacteria that cause toenail infections, and thus the feet suffer from grey nails. One of the superficial white onychomycosis may affect the color of the nail bed and have white horizontal lines on the toenails. Therefore, patients can first find out if they have a history of suffering from pediculosis, which may be secondary to gray nails due to untreated pediculosis in a timely manner, or they can go to the hospital for a fungal examination to determine if there is a fungal infection, which usually requires the application of medication for treatment.