Thumb nail crescent is generally a normal phenomenon, originating from the renewal and metabolism of the nail matrix, etc. If all the nails of the crescent is big, it may be due to hyperthyroidism and other diseases. The formation of the crescent on the nail is due to the newborn process of unkeratinized nails, belongs to the normal phenomenon in the growth of nails, in the process of newborn nails completely keratinized nails will become transparent, hard, and the newborn part of the white, its for the white crescent. For example, the thumb’s often subject to wear and tear, so the thumb nail will gradually form nail newborn, so the crescent will be larger. A larger white crescent on the thumb nail is generally normal, but a larger white crescent on all fingers may be due to a metabolic disorder such as hyperthyroidism. It is recommended to go to the hospital as soon as possible if you feel unwell or if the white crescents of all your fingernails are enlarged.