Why are there so many different facial hair types?

Have you seen any notable beards or mustaches lately? If not, don’t worry—there’s still plenty of time left in Movember to gaze upon the exotic displays of hair that this month has to offer. Facial hair is nothing new, but it’s during Movember—a one month event aimed at raising awareness of men’s health issues—that we get to see just how diverse it can be: some people don’t seem to be able to grow any at all, while others are sporting a dense forest of hair just a few days after shaving. So what gives? Why is there so much difference in hair growth among people?

When we think of hair, we typically think of what’s known as terminal hair—the pigmented, longer hair fibers that grow on our scalps and eyebrows. But there’s another kind of hair, so-called vellus hair, that blankets the human body. In fact, the only truly hairless parts of our skin are our palms, the soles of our feet, our lips, and portions of our sexual organs^1,2. We tend to see ourselves as hairless because vellus hair is small and non-pigmented, which makes it nearly impossible to see. But it is there, and it’s these barely visible hairs that will give rise to the many different flavors of facial hair types.

During embryonic development, hair follicles—the tiny, bulb-like structures of specialized cells that produce hair fibers—are formed into patterns across our bodies. These patterns set the stage for hair growth later in life^1-3. When we’re born, hair follicles are densely packed next to one another, but as we grow, other cells force their way between them causing them to spread out^2,3. This is partly how our hair styles are defined: the patterns formed during embryonic development mixed with the spacing out of hair follicles during growth. So if your beard is thick, patchy, or sparse, it may be due to the movement or number of hair follicles formed during development. It may also have to do with the transformation of vellus hair into terminal hair.

Initially, many of our hair follicles produce vellus hair, which is why babies appear relatively hairless^1-3. However, later in life and especially during puberty, hormones flood the body and affect many physical changes, including the transformation of vellus hair follicles into terminal hair follicles. It’s not entirely clear why some cells are sensitive to these hormones while others aren’t, but typically it’s the hair follicles in the pubic region, on the limbs, and on a person’s upper lip or jaw that are responsive^3,4. So if a person is able to grow a beard or mustache, it means their facial hair follicles were able to make the change from vellus to terminal hair.

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Humans: The naked primates

• Hair, or fur, is a powerful defense adaptation that most mammals have. Among its many qualities, hair is able to shield an animal’s skin from harmful ultraviolet light coming from the sun, and thus protects its DNA from potentially dangerous mutations. Hair also protects an animal’s body from heat loss. Yet, humans are among a rare group of mammals that have evolved to be less hairy. Read more about the mystery of our hairlessness and what it tells us about a belovedStar Wars character here.

Understanding how facial hair develops—from embryonic patterning to hormone driven changes—helps us understand how a person’s DNA may affect their Movember fur. Few studies have looked at the genetics of facial hair development in humans, but the few studies that have been done give us some clues.

One such study found that facial hair thickness in a group of about 6,600 Latin Americans was associated with a genetic factor affecting the EDAR gene⁵. This gene has previously been shown to affect the architecture of hair follicles during embryonic development³. It’s possible, then, that changes in the DNA affecting the EDAR gene may influence a person’s hair growth features. To that end, the researchers found that EDAR is involved in defining the pattern of facial hair follicles in mice—suggesting that it likely does the same in humans⁵. These findings tell us that heritable changes in the EDAR gene may be one of the reasons there is so much diversity in facial hair growth among people.

EDAR is not the first (and it likely won’t be the last) gene associated with various hair traits^1,3. Researchers are still in the early stages of understanding how DNA can influence various facial hair features, but these early findings give scientists promising directions for future studies. As research continues, we can be sure that the handlebars, flavor savers, Tom Sellecks, and many other varieties of facial hair will continue to make Movember a memorable month.

1. Trueb, Ralph M. Hair Growth and Disorders. Springer-Verlag Berlin And Hei, 2008.
2. Held, Lewis I. “The Evo-Devo Puzzle of Human Hair Patterning.” Evolutionary Biology, vol. 37, no. 2-3, Apr. 2010, pp. 113–122., doi:10.1007/s11692-010-9085-4.
3. Mou, Chunyan et al. “Generation of the primary hair follicle pattern” Proceedings of the National Academy of Sciences of the United States of America vol. 103,24 (2006): 9075-80.
4. Randall, Valerie Anne. “Hormonal Regulation of Hair Follicles Exhibits a Biological Paradox.” Seminars in Cell & Developmental Biology, vol. 18, no. 2, 2007, pp. 274–285., doi:10.1016/j.semcdb.2007.02.004.
5. Adhikari, Kaustubh, et al. “A Genome-Wide Association Scan in Admixed Latin Americans Identifies Loci Influencing Facial and Scalp Hair Features.” Nature Communications, vol. 7, Jan. 2016, p. 10815., doi:10.1038/ncomms10815.