The matrix helps make new cells. These cells then come together and push out of the skin. The lunula, or lunulae in the plural, is the visible portion of the matrix, although it may sometimes be hard to see. Skin color and other factors may make the lunulae more or less visible.

Lunulae that have a blueish tint could suggest Wilson's disease, a rare inherited genetic disorder in which copper accumulates in the liver, brain and other organs. Red lunulae may indicate heart failure, research shows.

Sometimes, you may only be able to see lunula on your thumbs, or possibly not on any fingers at all. In these cases, the lunula is most likely hidden under your skin. Though the connection is not completely understood, an absent lunula can indicate anemia, malnutrition, and depression.