Can beards protect against punches?

Beard Fact #1: The study of beards is called “pogonology,” from the Greek pogon for beard.

Beard Fact #2: In the Victorian era, doctors prescribed beards as a filter for airborne germs.

Beard Fact #3: Alexander the Great ordered his soldiers to shave off their beards, fearing that enemy forces would grab onto them in battle.

Physics Refresher

Sorry, but before we can get to beard science, we’re going to need to remind ourselves of a little bit of physics called the impulse-momentum theorem. If you’re a physics geek, you might recall that F • t = m • ∆v. Let’s focus on what this equation actually means: for a given change in an object’s speed, there’s an inverse relationship between (1) the force that causes the object to change speed and (2) how long that force acts for.

This theorem plays out in the real world all the time. For example, we know that if we drop an egg on a hard surface like a sidewalk, it’ll crack. But if we put something nice and squishy under our egg, it ends up just fine. This makes sense intuitively, but why does it actually work? The impulse-momentum theorem!

We’re taking an egg that’s moving at some speed and changing that speed to zero. If this change takes place quickly — like in the instant the egg hits a sidewalk — the force the egg experiences is high. But when we drag out the impact time with a squishy pillow, the egg experiences a lower peak force and doesn’t break.

This is the same principle that explains why the airbags in your car protect you — think about it. Lovely. That’s all the physics we’ll need today!

The impulse-momentum theorem for an egg-drop. Image: Manafzadeh

Battle Beards*

When a fist-fight breaks out, it’s pretty likely that someone’s going to end up with their jaw broken. A broken jaw is a big problem … and you can imagine it would’ve been even worse for our ancestors, who didn’t have access to the marvels of modern medicine. In a new study published in Integrative Organismal Biology, EA Beseris and colleagues from the University of Utah tested the hypothesis that facial hair — read: a beard — reduces the force that a human face experiences when it’s punched.

To do so, the researchers created an analog for human bone using a special kind of plastic. Then they bought some sheepskin and prepared plastic-fleece samples in three conditions: “furred” to model a full beard, “sheared” to model a trimmed beard, and “plucked” to model a clean-shaven (or waxed…? ouch) face. Once the samples were good to go, Beseris and colleagues used a drop-impact tester to give their samples a nice, scientific punch.

It turns out that the “furred” samples absorbed 30% more energy than the other samples, took longer to reach peak force, and experienced a lower peak force. The impulse-momentum theorem played out exactly as we’d expect! In other words, it looks like beards are really just handy dandy built-in face-airbags.

The researchers’ experimental design. Image: after Beseris et al., 2020 Figure 1

What Does It All Mean?

So, bearded guys are totally safe, right? Strangely, scientific studies have shown that men with beards don’t seem to win more often in mixed martial arts fights. This disconnect could result from special training among all MMA fighters to harness the impulse-momentum theorem in other ways, like “rolling” with punches. Or, it could be that beardless MMA fighters are breaking their jaws, but fighting through the pain and winning matches anyway. Still, if you happen to have a beard, don’t go looking for a fight just yet.

Based on their experimental results, Beseris and colleagues suggest that specialization for male-male fighting may have played a substantial role during human evolution, shaping several aspects of human anatomy — including facial hair. They point out that future studies should consider how facial hair varies among modern human populations in coarseness, density, and thickness, and how these variables might affect beards’ punch-dampening properties. Other studies might consider mechanisms beyond the simple impulse-momentum theorem that allow beards to protect facial skeletons.

There’s still plenty of beard-related research to be done, and I have a feeling that a lot of other researchers will soon be trying to get in on the action… But in the meantime, keep checking out iobopen.wordpress.com for the latest in cool, organism-centered biology!

By Armita R. Manafzadeh

Armita R. Manafzadeh is a PhD candidate studying the evolution and development of joint mobility at Brown University. Her interests include functional morphology, vertebrate paleontology, and biomechanics.

*Special thanks to Hannah I. Weller for this excellent section header.

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