Vertical Ridges, Lines or Bands on Fingernails
Vertical ridges and streaks on your fingernails are caused by different things. Your nails need blood, just like the rest of your body. Dark brown, black or gray streaks may occur on your fingernails or toenails as vertical, rather than horizontal lines.
If they are particularly dark in color, running from the tip of your nail to your cuticle, they may be because of dilated or burst capillaries. In most cases, lines like these typically occur because of an injury and are usually completely normal.
However, if you haven’t recently hurt your finger or toe and have lines like these along your nails, it may be unrelated to blood-flow issues. Some of these dark lines may be a sign of melanoma. Unlike other types of melanoma, this type — known as acral lentiginous melanoma (ALM) — isn’t related to sun exposure. ALM is a specific type of melanoma that appears on the palms of the hands, the soles of the feet, or under the nails.
Vertical lines in fingernails are most likely to be of concern when you haven’t had any injuries or impacts but the area surrounding the streak has damaged your nail. If you see any vertical, brown lines that run into your cuticle, contact your dermatologist as soon as possible to have a professional exam and diagnosis.