Warning! Do You Have That Half Moon Shape On Your Nails?

The phrase "moon on your nail" refers to the white, crescent-shaped area at the base of your fingernail, known as the lunula. The lunula is part of the nail matrix, which is the tissue that the nail protects and where new nail cells are produced. It's usually most visible on the thumb and less so on other fingers, though its visibility can vary from person to person.

The lunula is typically white because the thickened layer of skin under it obscures the blood vessels beneath. It's generally considered a sign of good nail health when it's visible, but the absence of a visible lunula doesn't necessarily indicate a problem.