Eyebrows do far more than frame your eyes and complete your look. They play key roles in protection, expression and anatomy. In this post I’ll discuss the anatomy of the eyebrow region, the muscles that control its position, how it performs functional roles, what changes occur with age or environmental factors, and finally what this means for your brow health.
Anatomy of the eyebrow
The eyebrow sits above the superior orbital margin (the bony ridge above the eye socket) and follows that supra-orbital rim. The area between the eyebrows is called the glabella which is most commonly referred to as a key site for botox injection. The skin over the bony ridge has a higher amount of fat and connective tissue, the galeal fat pad, than the upwardly surrounding tissue which gives it more tissue in which the hairs and associated glands are found. The hair follicle is deeper than an eyelash, but not as deep as scalp hair, and its growth cycle is shorter than the scalp too.
Function of the eyebrows
While we often focus on the cosmetic or beauty aspects of eyebrows, they serve several important functional roles.
PROTECTION OF THE EYE
The primary function of the eyebrow arch and eyebrow hair is to divert sweat, rain and moisture away from the eye itself. The combination of the projection of the fat pad with the underlying bony ridge acts like a sloping canopy to divert liquid laterally towards the side of the face. The brow hair gives a raised, slightly absorbent edge, and the combination means that the path of least resistance for water running down the forehead is away from the eye. Additionally the hair of the brow can help trap small debris before it reaches the eye region, either airborne or carried in liquid, which is then naturally wiped away by our hand.
SENSORY FEEDBACK
Related to the protection of the eye is the sensitivity of the area. Hair follicles are associated with nerve endings, especially Merkel cells that are especially sensitive to the most minute touch. In the brows, this helps to detect objects or movement close to the eye region, giving us an early-warning system of sorts. It is partly automatic and the resulting action can be as simple as a blink of the eye. The glebellar reflex is an example described in the literature in which the glabella (between the brows) is tapped, which causes the eyes to reflexively blink.
