By the way, doctor: What do these lines on my fingernails mean?

Q. Would you please tell me what it means when fingernails have vertical or horizontal lines?

A. Vertical lines or ridging is a natural part of nail growth. These lines may be more pronounced in some people's nails, particularly as they get older, but the ridges are usually mild. More severe, deep lines and splits may be seen with certain skin diseases, such as lichen planus.