Q: I have a red line that runs the length of my fingernail. Is this something to worry about?
A: A red line does not necessarily signal a worrisome medical condition. It may simply mean that the underlying blood vessels are more visible through a thinner nail plate — which happens to most of us as we grow older. Other times, a single red line may be caused by any one of a number of benign growths in the nail including a lipoma, which is a fatty tumor, a fibroma, or wart.
But in some cases, a red line running the length of your nail may mean something more serious, such as squamous cell nail cancer. If you notice red lines on several of your fingers, it could signal inflammation of the nail root by a variety of conditions such as psoriasis or lichen planus. Red lines on your nails are worth mentioning to your physician during your regular visit. If there is any change in the line, such as widening or darkening, have your nails evaluated by a doctor.
— Dermatologist Thomas Knackstedt, MD