AncestryDNA Traits
So much of your appearance—from head to toe—comes down to the complex interplay between genetics and environment. Even your feet can tell a story of your family’s origins. Most people have just one nail per toe, but some develop a double toenail, with an extra nail sitting next to the main one. Taking an AncestryDNA + Traits test can reveal how your inherited genes might impact your physical appearance and whether you're likely to have a double toenail on your little toe.
What Does Having a "Double Toenail" Mean?
Take a look at your feet, paying special attention to your pinky toes. Do you have just one nail there, or is there an extra one growing to the side? Often referred to as an accessory toenail or a petaloid nail, having a second toenail on one toe is a rare form of onychodysplasia, or abnormal nail development. They usually appear on the pinky toe, but can appear on other toes as well.
An affected toe may look like it has a nail that's wider than usual with either a complete split or slight indentation from the tip to the cuticle. These double nails can develop on anyone, regardless of age or place of origin. Some people develop an extra toenail on just one foot, while others have them on both.
Though double pinky toenails haven't been studied extensively, doctors have noted this variation for decades. It usually doesn't do much or affect your feet at all. In most cases, it's not noticeable unless you're looking for it.
Toenails and Genetics
Scientists believe that split toenails, also called “accessory” or “double toenails,” are autosomal dominant. That means they often recur in families and only one biological parent has to carry the gene to pass it on to their child. However, more research is needed to narrow down the exact genes associated with its development.
Curious about double toenails, especially on the little toe, the AncestryDNA team sought to investigate. Over 850,000 people answered the question, "Do you have a double toenail on either of your pinky toes?" By comparing their answers to their genetic profiles, AncestryDNA scientists identified over 290 DNA markers related to the trait. At least 5% of the variation in whether the survey respondents had a double toenail could be explained by differences in their DNA.
What Else Can Cause Accessory Toenails?
Not everyone with a split pinky nail was born with it. In some cases, they form as a physiological response to trauma on the affected toe. Frequent injury can cause the skin surrounding the nail to thicken and, in some cases, result in hyperkeratosis. The hard part of your nails is made of keratin, so when your body produces excess on your toe, you might end up with an extra nail.
They may also be caused by footwear choices. One study acknowledged that women sought care for double toenails on their pinky toes more than men. However, researchers also noted that this was likely due to them acquiring more foot problems by wearing narrower shoes designed for fashion over function. Because overly narrow shoes can pinch or constrict the feet, they can irritate the extra nail, making it more likely to be discovered.
Interesting Facts About Toenails
A double toenail is usually asymptomatic. They don't typically hurt and are often found by chance. In one study, one in three people reported discomfort from their extra toenail and pain only affected one in five. Of those reporting pain, most were elderly and had a splayfoot, which causes the forefoot to spread apart and changes how the foot bears weight.
In some cases, an injury can cause a new toenail to grow under an existing toenail. This condition, known as retronychia, results when the nail plate grows backwards or downwards. The new layers of toenail have nowhere to go, forcing them into the nail fold. Unlike cases of petaloid nails, if your new toenail grows under a toenail that’s already present, it's likely to cause swelling and irritation, or could even lead to an infection if left untreated.
Some scientists believe a double nail is an incomplete form of polydactyly, the development of extra digits on the hand or foot. Because of this, medical professionals usually perform X-ray imaging to check the underlying foot structure before treating these nails if they cause pain.
Curious about the genetic or environmental influences on your feet? Whether you've got a split nail, flat feet, or a longer second toe, the answers may be waiting in your family tree. Explore the many traits that make up who you are through an AncestryDNA + Traits test. If you've already taken a test, see what your genes suggest about your second toenail—and other traits—with an Ancestry subscription today.
