Hidden traits of the human body
The human body carries many small signs of genetic variation and evolution. Some traits are easy to notice, while others remain almost invisible. One example is the preauricular sinus, a tiny opening near the ear. As described in the article, it is “a tiny hole, pit, or dimple located near where the face meets the upper ear cartilage.”

What a preauricular sinus is
Medically, this feature is known as a congenital fistula beneath the skin. The visible mark is only the surface opening, while the actual sinus is a small tunnel under the skin that can vary in depth and shape. Although it is called a fistula, it usually ends blindly rather than connecting to another structure.

How it develops
The condition forms during early fetal development. Between the fifth and seventh weeks of pregnancy, the external ear develops from six small tissue structures called the Hillocks of His. If these tissues do not fuse completely, a narrow passage may remain. In this way, the preauricular sinus is “a small developmental remnant of an incomplete fusion process.”

How common it is
The feature is relatively rare and varies across populations. In the United States and Europe it appears in less than 1% of people, while in some Asian populations it may reach 4–10%. It usually occurs on one ear, although some individuals have it on both sides. Genetics also plays a role, and the trait can be inherited.

Symptoms and treatment
Most people with a preauricular sinus experience no symptoms and do not require treatment. However, the opening can sometimes become blocked, allowing bacteria to grow and cause infection. In such cases, doctors may treat the infection with antibiotics or drainage. For recurring problems, surgical removal of the sinus tract may be recommended.