Vertical lines on the nail are due to a variety of causes. The first thing to consider is the longitudinal nail ridge, which is a specific change in the nail and is a normal physiological phenomenon. Next, nail dystrophy is a possible cause, which may be related to vitamin deficiency, micronutrient deficiency, use of alkaline detergents, nail trauma, and certain systemic diseases such as anemia, acromegaly, pulmonary dysfunction, and hypothyroidism. Certain congenital factors, such as congenital ectodermal dysplasia or herpetic epidermolysis bullosa, can also contribute. Also, consider the possibility of nail fungal disease, which is mainly caused by fungal infections, commonly including Microsporum canis, Microsporum ferrugineum, and Candida. Predisposing factors include tinea pedis, nail trauma, excessive sweating of the feet, diabetes, and AIDS.