Black lines on fingernails. What's going on?

Fingernails show black lines, which may be caused by pigmentation caused by nail trauma, or by a lack of trace elements, or may be caused by fungal infection. Another cause is nail nevus, which is rare. It is recommended to judge the cause according to the length of nail lines and the time they appear, combined with other symptoms of the body, such as poor recent rest, irregular diet, which may be caused by malnutrition and secretion disorders, pay more attention to rest, and then supplement multidimensional elements.