Toenails with horizontal lines are mostly considered to be caused by the lack of vitamins and trace elements, trauma, nail fungal disease, nail groove inflammation and other reasons. 1. Lack of vitamins and trace elements: due to long-term dietary irregularities or picky eating, partiality, resulting in a lack of vitamins and calcium, iron, zinc and other trace elements, resulting in insufficient synthesis of nail keratin, easy to form the toenails have horizontal lines. 2. Trauma: If the toenail is violently impacted or extruded, resulting in nail plate damage, blood vessel rupture, insufficient blood supply to the local tissues, it is easy to appear the situation of toenail with horizontal lines. 3. Nail fungal disease: due to the lack of attention to foot hygiene, resulting in fungal infection of the toenail, causing inflammatory lesions of the nail plate and nail bed, thus appearing to have horizontal lines on the toenail. At the same time also accompanied by nail turbidity, thickening, atrophy and other manifestations. 4. Nail groove inflammation: due to the nail groove and its nearby tissues puncture, abrasion, ingrown nails and other factors caused by purulent bacterial infection of the toenail, resulting in poor blood circulation, nutrient supply obstacles, thus appearing in the toenail has horizontal lines of the situation. If the horizontal lines on the toenails are slight and inconspicuous, follow-up observation can be done, if it is more obvious and uncomfortable symptoms, it is recommended to consult a doctor in a timely manner.