The main function of the eyebrows is to prevent moisture, mostly salty sweat and rain, from flowing into the eye, an organ critical to sight. The typical curved shape of the eyebrow (with a slant on the side) and the direction in which eyebrow hairs are pointed, make sure that moisture has a tendency to flow sideways around the eyes, along the side of the head and along the nose. The slightly protruding brow ridges of modern humans could also still play a supporting role in this process. Together with the eyebrows, the brow ridges also shade the eyes from sunlight.
Eyebrows also prevent debris such as dandruff and other small objects from falling into the eyes, as well as providing a more sensitive sense for detecting objects being near the eye, like small insects.
Eyebrows also have an important facilitative function in communication, strengthening expressions like surprise or anger. In African cultures, raising and lowering the eyebrows is used as a confirmation sign (the equivalent of nodding).
It is common for people to pluck their eyebrows to maintain a clean and fashionable appearance with the use of tweezers and waxing. Threading eyebrows has also become a popular method because it does not pull at the skin. All of these methods can be painful for some seconds or minutes due to the sensitivity of the area around the eye but often this pain decreases over time as the individual becomes used to the sensation.
Some people also choose to pierce their eyebrow.