Double little toenail

How it works

In some people, a groove or a split divides the little toenail into a large inner part and a narrow outer part. In one series of 58 patients, the outer part was 2 to 7 mm wide, and 54 had it on both feet¹.

The small part can have its own nail root, called the matrix. Ultrasound in one family in Italy showed a small second matrix beside the main one⁴.

The trait runs in families¹³. A 2005 survey of one village said a single dominant gene controls it³. A 2016 genome scan of 3,701 people found no such gene². The trait is partly inherited (heritability 34.3% to 57.4%), probably through many genes with small effects². The cause is not known.

How common it is

All population figures come from China. A 2016 study found it in 58.97% of 2,980 Han Chinese in Jiangsu Province and in 51.15% of 721 Uyghurs². A survey of one village in Shaanxi Province found 79.17%, with little difference between men and women³. Both studies sorted the trait into more than one grade or type²³. So the figures can depend on how mild a form is counted.

Nobody has measured the rate outside China. One skin doctor calls it common but underdiagnosed¹. Other authors call it rare⁴.

Try it

1. Take off your socks and sit in good light.
2. Look at the nail of your little toe. Check its outer edge, the side away from the other toes.
3. Look for a groove or a split that sets off a narrow strip of nail.
4. Check the other foot. It is usually the same on both sides¹.

Is it a problem?

No. It is a harmless variation, and most people never ask for treatment¹⁵. In one series, about a third of patients had discomfort and a fifth had pain. Most of them were older¹. The extra nail can press against a shoe¹. These patients were seen in skin clinics, so the true share is probably lower. It is not the mark of one ethnic group¹. Mention it to a doctor if it hurts in shoes, or if a split appears after an injury.

History and culture

It was first described in Germany in 1969⁶. Chinese legends say only Han Chinese have the split nail². One legend dates it to the time of the Yellow Emperor⁵.

The evidence does not support this. In Uyghurs, who have mixed East and West Eurasian ancestry, the trait did not follow the share of East Asian ancestry². One doctor saw 58 patients with it in skin practices in seven countries, from Norway to Thailand. Only one was Han Chinese¹. He concluded it is “certainly not a special racial or ethnic feature”¹.