Vertical nail lines in babies are usually caused mainly by malnutrition, systemic diseases and localized nail lesions. 1. If a baby is malnourished and lacks a certain amount of vitamins and trace elements, such as calcium and iron, it may lead to the appearance of vertical lines on the nails. 2. The nails of patients with certain systemic diseases, such as anemia and hypothyroidism, may also develop vertical lines. 3. Localized lesions of the nails themselves may also lead to the appearance of vertical lines on the nails, commonly known as lichen planus, eczema, etc. If the color of the vertical lines on the nails is darker, it may be related to nevus of the mother of nails or traumatic injuries. There may be other reasons for the vertical lines on the nails of infants, so it is recommended to go to the hospital in time, improve the examination to clarify the cause of the disease, and then give targeted treatment or treatment under the guidance of the doctor.