It’s not uncommon to only see the half-moons (lunula) on your thumbs. A small or missing lunula is not usually something to worry about, as they are often hidden under the cuticle or the skin at the base of the finger. Missing lunulas may be a result of trauma to the finger or possibly a sign of anemia, malnutrition, or depression. If you are experiencing fatigue or weakness along with missing lunulas, see your doctor to determine the cause.