Crossed nails are not necessarily a disease, but should be analyzed on a case-by-case basis. Transverse nail lines are the result of a temporary blockage in the formation of the protein of the nail plate. Crossed nails can be caused by a variety of diseases, such as nail fungus and enteropathic acrodermatitis. Crossed nails can also be caused by habitual twitching and deformities, mostly in the nails of the thumb. However, frequent habitual transverse damage to the nail epithelium as well as the nail plate of the thumb with other fingers can cause loss of the nail epithelium, and transverse grooves may appear in or around the middle of the nail plate, or the nail file may be used to grind transverse lines on the nail surface during manicure, and this condition is not due to disease. If crossed nails appear, it is recommended to consume foods rich in vitamin A. Calcium can also be supplemented appropriately to facilitate nail development and growth. In addition, patients should be careful not to pick their nails to reduce mechanical stimulation of the nails.