Question Corner: Why are the bases of our nails white?

Half moons in the nail

When we look at our nails, we see a white portion at the base, what is this?

P.J. Anish, Bengaluru

According to the American Academy of Dermatology, there are three parts to a finger nail.

The small, white colour, half-moon shaped feature that can be seen at the bottom of the nail, especially in the case of thumb, is called lunula.

The lunula is present under the skin and is part of the matrix which can be seen through the transparent nail plate proximal to the pink nail bed.

There is nothing to worry if lunula is not seen. As per a 1996 paper in the

Journal of American Academy of Dermatology, lunula appears by week 14 of gestation.

Alterations in the morphologic features or colour (or both) of the lunula can be an indication of either a cutaneous or a systemic disorder.

For instance, the white lunula turns blue in the case of Wilson’s disease. It may become red in cardiac failure or due to carbon monoxide poisoning. Generally, lunula becomes smaller or absent in old age.

A.K. Cherian, Chennai

This week’s questions

Why is glass transparent to visible light, but opaque to ultraviolet radiation?

Bhavani, Bengaluru

What is the growling noise that we hear when the stomach is empty?

Yogesh Jethewad, Chennai

What causes a rise in body temperature when we have fever?

Umesh Chandra Thakur, New Delhi

Do bats migrate long distances?

Sharath Chandra Kommu, Hyderabad, Telangana

Unlike other tropical vegetables, carrots wilt in three or four days. Why is it so?

P. Suresh and Palaniselvam Kuppusway, Gobichettipalayam,

Tamil Nadu

Readers can send their questions/ answers to questioncorner@thehindu.co.in