The crescent-shaped whitish area of the bed of a fingernail is a extremely important and sensitive nail part and you should be very careful not to damage it.
This whitish half-moon is called lunula. The lunula is actually the visible part of the nail’s root and should not be damaged in any way because if you damage it your entire nail will be permanently deformed.
However, if you just damage the rest of the nail and it falls off or is surgically removed the lunula will remain intact and in its place. It is not really white, but only appears so when it is seen through the nail.It’s most visible on the thumb but not everyone’s lunula is visible. In some cases, the eponychium, the thickened layer of skin surrounding fingernails and toenails, may partially or completely cover the lunula.