I have horizontal ridges in my nails. How did this happen?

Horizontal ridges on the nails can represent very benign causes. The most common cause of horizontal ridges on the nails is called “Beau's lines.” Horizontal ridging of the nails is trauma to the nail matrix, which is located just behind the cuticle. There are also a few, rarer nail conditions that can portend liver or kidney issues. Nail changes are worth getting checked out by a board-certified dermatologist.