White semicircles under the nails are normal and do not require treatment.
The white semicircle under the nail is called a semilunar scar and is normal nail tissue. This portion is incompletely keratinized keratinocytes and is part of the newborn nail. This part gradually moves forward and continues to keratinize and inactivate, eventually forming a protective nail.
The meniscus is usually small in childhood, increases in size with age, and becomes smaller again in old age. Usually the thumb has a larger meniscus and the little finger has a smaller one. It is normal for some people to have no meniscus on their nails.
The size and color of the meniscus vary from person to person and do not reflect health or disease development, nor are they used to diagnose disease.