Finger nails with horizontal stripes may be caused by pigmentation, micronutrient deficiencies and fungal diseases. 1. Hyperpigmentation: When melanin cells are active in the patient’s body, it will lead to localized hyperpigmentation, resulting in brown or black horizontal stripes on the nails. 2. Trace element deficiency: If the patient’s body is deficient in trace elements, such as calcium and zinc. This will make the nails themselves malnourished, which will lead to pigmented changes in the nail stripes and horizontal stripes. 3. Fungal disease: Fungal disease patients due to fungal infection of the nail plate, resulting in deformation and thickening of the nail plate, and the growth of horizontal stripes. There are many other causes of long horizontal finger nail lines, such as psoriasis, lichen planus and chronic digestive diseases. If the patient’s fingernail long horizontal lines, should go to the hospital in time to identify the cause of the disease, and active treatment.