These half-moon shapes are called lunula in medical terms. This is common in every individual, those who cannot see lunula on their nails, means they have a vitamin deficiency or are suffering from a medical condition.

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.

People with B-12 deficiency may notice that their lunulae disappear.

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.