The crescent moon on the fingernail is also known as half-moon mark, crescent white, some people call it a small sun. Fingernail crescent generation is due to the nail growth process in the nail bed in the middle of the cell growth rate is faster, the two sides of the cell growth rate is relatively slow, the lower part of the nail without blood vessels through the formation of the crescent-shaped white trace that is half-moon mark. Fingernail crescent is the body’s newborn cells, the crescent of the presence and size of the finger depends on the frequency of use, the more frequent use of the finger, stimulate the nail growth rate faster, the larger the crescent. On the contrary, the slower the nail growth rate, the smaller the crescent may be or even invisible to the naked eye. As the metabolism slows down with age, the crescent may also disappear. The size of the crescent may also reflect some diseases. Sudden enlargement of the crescent or a sudden increase in the number of crescent teeth over a short period of time may be a sign of hyperthyroidism. The crescent may disappear in cases of serious illness or severe malnutrition where the new cells of the nail do not receive enough nutrients to produce keratinocytes.