In humans, eyebrows serve two main functions: first, communication through facial expression, and second, prevention of sweat, water, and other debris from falling down into the eye socket.

[citation needed] Another theory holds that clearly visible eyebrows provided safety from predators when early hominid groups started sleeping on the ground.

[1][clarification needed] Recent research, however, suggests eyebrows in humans developed as a means of communication and that this is their primary function.

[4][5] Cosmetic methods over the centuries have been developed to alter the appearance of eyebrows by adding or removing hair, changing the color, or changing the position to meet the aesthetic ideal of the time, for example, by tinting the eyebrow with permanent dye, similar to hair colour, often in order to darken them.

Several options exist for removing hair to achieve a thinner or smaller eyebrow, or to "correct" a unibrow, including manual and electronic tweezing, waxing, and threading.

It is not a new phenomenon, with the earliest description of brow lifting published in medical literature in 1919 by French surgeon Raymond Passot.

In the 1970s, doctors started injecting patients' eyebrows with botox or similar toxins to paralyse the muscles temporarily, causing the brow to raise.

[8] Japanese women and men from the 8th century practiced hikimayu: shaving or plucking the eyebrow hair and painting smudge-like ones higher on the forehead or pencilling in thin ones in a different place.

This process, also called cosmetic tattooing or microblading involves an eyebrow artist implanting pigments in small, precise cuts that mimic the look of hair.