Ridges in your nails are visible lines or dents in your fingernails or toenails. The ridges may run vertically (up and down) or horizontally (across) your nail. Ridges in your nails can be a sign of a health condition or a previous injury to your nail. In some cases, they’re harmless.

Beau’s lines are horizontal ridges or dents in one or more of your fingernails or toenails. They’re a sign that an illness, injury or skin condition interrupted your nail growth. Treating the underlying cause will allow new, smooth nails to grow again.

Lines running from the bottom of the nail to the tip are the most common form of ridges in fingernails, affecting about 20 percent of adults. In the vast majority of cases, it’s just a sign of aging, says Ivy Lee, MD, a board-certified dermatologist based in Pasadena, California.

Three is spooning. It can happen if you have iron-deficient anemia or liver disease. Four is called "a Beau's line." It's a horizontal line that indicates a previous injury or infection. Five is nail separation. This may happen as a result of injury, infection or a medication.

Longitudinal ridging, which is clinically known as onychorrhexis, occurs on the nails and may appear as vertical striations or lines that originate from the base of the fingernail and continue to the end of the nail.