When we think of rare physical traits, we usually imagine certain striking features that immediately draw attention. But sometimes, unusual traits are so small and subtle that they go completely unnoticed, even by the person who has them. One such example is that tiny hole or dimple located near the top of the ear. This hole is in fact known as preauricular sinus. At first glance, it might look like a faint birthmark or an oddly placed piercing, but it’s neither.

A preauricular sinus, also called a preauricular pit or fistula, is a small congenital opening that forms during early fetal development, typically around the sixth week of gestation, Medical News Today noted. It occurs when parts of the ear don’t fuse completely, and it’s often hereditary, meaning it can run in families. The pit can appear on one or both ears, though having it on both sides is quite rare.

Most people with this small opening never experience any problems, and it’s considered a harmless genetic quirk. In some cases, however, the pit can become infected, causing swelling or discomfort. Such infections can usually be treated with antibiotics. However, if they keep coming back, they might need to be removed surgically.

While this ear mark is an uncommon feature, it is a fascinating reminder of how tiny variations in human development can make each of us a little different.

According to Business Insider, these tiny holes may trace back to our ancient aquatic origins. Evolutionary biologist Neil Shubin has suggested they could be a leftover feature from fish gills, though this theory hasn’t been scientifically proven. While the idea is fascinating, the condition itself is harmless.

Ultimately, they’re just a small but interesting reminder of how our bodies carry traces of the past.