An eyebrow is an area of short hairs above each eye that follows the shape of the lower margin of the brow ridges of some mammals. Often underestimated, eyebrows serve a multitude of functions, ranging from the practical to the expressive. They are not merely aesthetic features; they are integral to eye health, non-verbal communication, and even facial recognition.
Eyebrows play a crucial role in protecting the eyes, acting as a first line of defense against environmental elements. They protect our eyes from moisture and light.
One of the primary functions of eyebrows is to prevent sweat, water, and other debris from falling down into the eye socket. Eyebrows are nature’s sweatband. The curved eyebrow arch is no coincidence, either. That curve wicks the moisture off the skin and around the arch, helping it drain along the sides of your face. Ever notice how your eyebrow hairs grow outward, toward the sides of your face? That helps direct any moisture away from your eyes toward the side of your head. Without eyebrows, all of this would run right into your eyes. Fortunately, your eyebrows serve as a “sweatband,” helping to block the flow of sweat and lift it off of your face where it can evaporate before it gets to your eyes. Secondarily, this action of wicking and lifting up of sweat also serves as a cooling function! They catch particulate matter from dropping into your eyes or further down onto your face. Many of these particulates are very small and almost invisible to the naked eye, making it hard to believe that eyebrows are as necessary as they are.
The brow bone and eyebrows are like mini sun visors. Eyebrows also offer a degree of sun protection. Prior to sunglasses, humans relied on hats, the shade, their hands, and their eyebrows to help shield the eyes from direct sunlight.
In addition to protecting your eyes from sweat, the eyebrows also serve as a filter. They catch particulate matter from dropping into your eyes or further down onto your face. Without your eyebrows filtering these particles away from your eyes, you’d be far more susceptible to eye allergies and infections.
Read also: Vertical Brow Wrinkle Guide
Recent research suggests eyebrows in humans developed as a means of communication and that this is their primary function. Humans developed a smooth forehead with visible, hairy eyebrows capable of a wide range of movement.
Eyebrows are an important part of human expression and communication. They allow us to show our emotions. Eyebrows are a key player in facial expression. You can look at cartoon graphics of eyes and eyebrows - without any other features - and accurately determine emotions like anger, confusion, sleepiness, happiness, or fear. The eyebrows’ angle, arch, and movement are important non-verbal communicators. One raised eyebrow expresses skepticism or interest. Two raised eyebrows can express surprise. Our human brains are naturally wired to read, assess, and translate what eyes and eyebrows express without us having to think about it.
Beyond looks and emotions, eyebrows are also more generally important for facial recognition. A social study done in 2003 used manipulated photos of famous people - eliminating the eyes or the eyebrows, evaluating which features were the most recognizable. It turned out study participants could recognize an average of 60% of the individuals when the eyebrows were there (without eyes), but only 40% were recognizable when the eyebrows were gone, and only the eyes remained. Scientists manipulated the photos so that they’d either have no eyes or no eyebrows. Subjects could still identify the famous faces 60 percent of the time when they lacked eyes. But when the faces lacked eyebrows, subjects could identify them just 46 percent of the time. Scientists said this indicates that eyebrows are just as important as - or maybe more important than - eyes in allowing us to recognize faces.
Scientists have established that the shape, color, and thickness of your eyebrows are inherited traits. The scientists found a strong relationship between inheritance of specific genes and eyebrow appearance. Four separate genes may affect eyebrow hair texture, one gene may determine eyebrow shape, five genes affect eyebrow hair color, and one gene determines whether or not you develop a monobrow. However, environmental factors also have a lot to do with how your eyebrows look. Years of waxing or tweezing your eyebrows can permanently affect their shape. Injuries to the skin near your eyebrows can also affect hair growth and eyebrow shape.
Just as eyebrow characteristics are inherited, so are abnormalities affecting the eyebrows. One of the most common abnormalities affecting eyebrows is madarosis, or loss of eyebrows. The term madarosis can also refer to loss of eyelashes. Some autoimmune diseases, like alopecia, madarosis, or other health conditions, can reduce or eliminate eyebrows due to hair thinning or loss.
Read also: The Truth About Real Hair Eyebrow Wigs
Lashes/brows, while rooted in function, have also taken center stage in the world of aesthetics and cultural expression. Across time and cultures, they have been adorned, modified, and celebrated in myriad ways.
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. In various cultures, eyebrows play a role in rites of passage or religious ceremonies. For instance, in some Hindu traditions, a baby’s first haircut often includes shaving the head but leaving the eyebrows untouched, symbolizing purity and protection.
From the pencil-thin eyebrows of the 1920s to the lush, bold brows popularized in the 2010s, eyebrows have seen a roller-coaster of trends. Cosmetics tools such as eyebrow brushes, shaders, and pencils are often used to define the eyebrow or make it appear fuller. These can create an outline for the brows or mimic hairs where there are sparse areas. Brow gels are also used to create the look of thicker brows by adding texture to the hairs, making them appear fuller and more defined. Similarly, eyelash extensions, mascaras, and serums have evolved as beauty staples, reflecting changing fashion statements.
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. The most common method is to use tweezers to thin out and shape the eyebrow. Waxing is becoming more popular. Lastly, there is threading eyebrows, where a cotton thread is rolled over hair to pull it out. Small scissors are sometimes used to trim the eyebrows, either with another method of hair removal or alone. All of these methods can be painful for 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 it. In time, hair that has been plucked will stop growing back. Some people wax or shave off their eyebrows and leave them bare, stencil or draw them in with eye liner or tattoo them on.
In the 21st century, tattooing became popular as a way to achieve and maintain an eyebrow shape, using a coil machine, rotary machine or a manual tool containing a row of needles. This process, also called cosmetic tattooing or microblading involves an eyebrow artist implanting pigments in small, precise cuts that mimic the look of hair. To create a fuller look, eyebrows can be cloned in an eyebrow transplant. Individual strands of the eyebrow are created to mimic a natural-looking eyebrow of the desired shape. The process of eyebrow transplant is quite similar to the process of hair transplant. In this process as well, follicles from an active area are transferred to the area where there are no hairs. Follicles are mostly taken from the back of the head because it is the best harvesting site when it comes to hairs. The healing process after an eyebrow transplant is similar to the process of tattoo. In this process, patients may experience light bruising and crusting of the skin. An eyebrow lift is a cosmetic surgery to raise the eyebrow, usually to create a more feminine or youthful appearance. It is not a new phenomenon, with the earliest description of brow lifting published in medical literature in 1919 by French surgeon Raymond Passot. Brows can be affected during a face lift or an eye lift.
Read also: Comprehensive Guide: Darkening Eyebrows
Eyebrow hair follicles share the same basic structure as hair follicles elsewhere on the body, but are distinguished by their shorter anagen (growing) phase. Knowledge of the hair follicle structure and cycle is important for understanding the pathophysiology of alopecia, as diseases affecting the stem cell portion of the hair follicle in the bulge region may cause permanent hair loss. Furthermore, therapeutic agents that target distinct phases and hormones involved in the hair cycle may be useful for promoting hair growth.
The lower portion of the hair follicle comprises the hair bulb, which is composed of rapidly proliferating matrix cells that produce the hair shaft. These layers are composed of characteristic intermediate filament keratins, enzymes, and adhesion molecules. The ORS of the hair follicle is continuous with the epidermal basal layer and contains melanocytes, Langerhans cells (dendritic antigen-presenting cells), and Merkel cells (specialized neurosecretory cells). Pigment in the hair shaft is produced by melanocytes located in the hair bulb that transfer melanin to keratinocytes in the developing hair shaft cortex and medulla. As the matrix cells differentiate and move upward, they are compressed by the rigid IRS, whose structure determines the shape of the hair shaft. The dermal papilla, which is composed of specialized mesenchymal cells located at the base of the follicle, is thought to control the proliferation of matrix cells and thus the size of the hair shaft. The bulge consists of a cluster of biochemically distinct cells located in the ORS, near the insertion of the arrector pili muscle. Bulge cells have the characteristic properties of epithelial stem cells: they are slow-cycling (quiescent) and are thought to persist for the lifetime of the hair follicle. It is believed that the bulge population contributes to epithelial cells that proliferate and regenerate the new lower follicle during the growing stage of the hair cycle. Epithelial stem cells in the bulge portion of the ORS may also serve as a reservoir for epidermal and sebaceous-gland cells. The bulge region of the hair follicle is especially rich in nerve endings and Merkel cells. Hair follicle bulge cells express CD34 in mice and keratin 15 in humans.
Hair morphogenesis is initiated in utero through complex interactions between the epithelium and underlying dermis.
Because eyelashes and eyebrows are so closely linked to eye protection, it’s important to maintain good hygiene and avoid habits that can weaken or damage them. Typically, our eyebrows and eyelashes stay healthy with minimal intervention. Nevertheless, problems like ingrown hairs, inflammation, or hair loss can occasionally occur. Should you encounter any issues with your eyebrows or eyelashes, don’t hesitate to reach out.
