Is There an Evolutionary Reason or Purpose for Acne?

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Acne May Be a Side Effect of Losing Our Body Hair as We Evolved, an Adaptation That Makes Childbirth Easier, or Even a Way That Nature Prevents Teens from Having Kids Too Early

• Evolution: A Crash Course
• 1. The “Side Effect” Theory: Acne Is a Byproduct of Natural Selection
• 2. The “Slippery Baby” Theory: Acne Is a Consequence of Natural Selection
• 3. The “Nature’s Contraceptive” Theory: Sexual Selection Explains Why Acne Is Here to Stay

Acne is officially defined as a disease. It certainly feels that way to people who suffer from acne. However, the fact that acne is so incredibly common throughout the world begs the question of whether there could be some reason why evolution kept acne around. Does acne serve some evolutionary purpose, is it just a glitch of our biology, or is there another explanation?

Scientists have come up with three theories to explain why we might have evolved to develop acne:

1. The “Side Effect” Theory: This theory suggests that acne developed as a side effect of us losing our body hair during evolution. As humans evolved from hairy apes, we lost body hair faster than we lost skin oil. When there was no longer enough body hair to push skin oil out of pores, skin oil ended up staying inside pores, clogging the pores, and ultimately causing acne.
2. The “Slippery Baby” Theory: This theory suggests that as babies, we need a lot of skin oil on the face and shoulders to lubricate our passage through the birth canal. However, later in life, this skin oil can become problematic and cause acne.
3. The “Nature’s Contraceptive” Theory: This theory suggests that teen acne was actually an evolutionary advantage for humans. Teenagers who developed acne were temporarily less attractive to the opposite sex and were less likely to have children early, when they would have struggled to raise them. By the time the acne cleared in their late teens or early twenties, they were more mature and better able to raise healthy kids who survived and passed on their genes.

To better understand these three theories, we need to take a step back and look at exactly how evolution works. I find this stuff fascinating, so feel free to go on this exploration with me, but if you’re good to go at this point, the takeaway is that we have these three possible explanations, but they are just theories. They are not fact. Acne could be the result of one of these theories, a combination of these theories, or it might not be evolutionary at all. Evidence shows us that hunter-gatherers don’t tend to have acne, so it might be something about how we live in modern society that’s causing acne. 

Evolution: A Crash Course

Charles Darwin proposed the Theory of Evolution by Natural Selection in the mid-19^th century. First, let’s unpack the name of his theory:

• Evolution: The word “evolution” means change in the characteristics of a species over successive generations. In other words, in the scientific sense, we can say that humans as a population evolve over thousands of years, but we cannot say that an individual person evolves over her lifetime.
• Natural Selection: Natural selection means that conditions in nature (the environment) select which individuals in a population get to survive and pass on their genes. People often describe this as “survival of the fittest,” meaning that the individuals who “fit” the current environment best will be more likely to survive, thrive, and reproduce.¹

Now let’s look at an example of how evolution works.

Example: Natural selection at work

Imagine a species of snakes whose skin can either be green or orange, in the same way that human skin can vary in color. Suppose that this variation is genetic, so that a green snake will have green offspring, and an orange snake will have orange offspring.

Let’s pretend this population of snakes starts out with equal numbers of snakes of each color.

This is natural selection at work. The environment has “selected for” green skin.

Even though this is a made-up example, it is realistic because many species evolve to blend into their surroundings in just this way.

If you want to take a look at a real-life example of evolution, expand the section below.

Now that we know how natural selection works, we are almost ready to dive into the theories of why humans have acne, but for the theories to make total sense, we first need to take a quick look at a special type of natural selection called sexual selection.

Sexual selection

In sexual selection, it is not the environment but members of the opposite sex that select for particular traits. When individuals of one sex choose mates of the opposite sex, they find certain traits more attractive.

For example, in some frog species, female frogs choose the males with the deepest croaks during the breeding season. As a result, these males then have the best chances of mating with females and fathering offspring, who will inherit deep croaks. In other words, female frogs select for deep croaks, which means that over generations, more and more frogs in the population will have deep croaks. This is sexual selection at work.²

Now we have all the tools we need to understand the three current theories on why humans evolved to have acne:

1. The “Side Effect” Theory: This theory uses the principles of natural selection to explain why humans today have acne.
2. The “Slippery Baby” Theory: This theory also uses the principles of natural selection to explain why humans today have acne.
3. The “Nature’s Contraceptive” Theory: This theory uses the principles of sexual selection to explain why humans today have acne.

Let’s look at each theory in more detail to see if it holds water.

1. The “Side Effect” Theory: Acne Is a Byproduct of Natural Selection

Although this kind of theory is impossible to prove, the scientists put forward some evidence that supports their idea. They noted that the only animals who can develop acne are hairless, including:

• Mexican Hairless Dogs: This breed of dogs is the only type of animal besides humans that naturally develops acne. In fact, the dogs’ acne looks similar to human acne, with excess skin oil and clogged pores.

• Rhino mice: Even though these hairless mice do not naturally have acne, scientists can induce acne in them in order to study how acne develops and how to treat it. The fact that scientists can only induce acne in hairless mice suggests that lack of body hair is an important condition for developing acne.³

Now let’s look at the second theory, which suggests that acne actually benefits the human species.

2. The “Slippery Baby” Theory: Acne Is a Consequence of Natural Selection

Like the first theory, the “slippery baby” theory is impossible to prove, but Dr. Shannon points out an interesting pattern:

• Humans are the species that struggles most during labor and also the only species that suffers from acne: Because our brains are so large relative to our bodies, a newborn baby’s head has a hard time passing through its mother’s pelvis. That’s why humans have more difficulty in labor than any other animal species. There is even a special term, “dystocia,” for obstructed labor in humans. Dr. Shannon argues that it’s not a coincidence that we are also the only species that struggles with acne.⁶

Finally, let’s examine the third theory, which suggests that acne might help the human species in a different way.

3. The “Nature’s Contraceptive” Theory: Sexual Selection Explains Why Acne Is Here to Stay

Again, there is no way to prove this theory is correct, but here are some observations that support it:

• Acne is almost universal in teens: Some studies have found that up to 85% of adolescents (teens) and up to 100% of teen boys experience acne to some degree.
• Acne occurs on visible parts of the body: Acne develops exactly where potential mates are most likely to see it, such as on the face and upper body.
• Some ethnic groups that reach puberty at a later age are free from acne: The Kitavan Islanders of Papua New Guinea, a hunter-gatherer society, very rarely develop acne. In this population, puberty is delayed compared to most Western societies. For example, Kitavan girls first menstruate at age 16, compared to American girls who first menstruate at 12, on average.⁸ In other words, perhaps people in those societies do not need acne to prevent them from sexual activity at too early an age, because they can only have kids when they are older anyway.⁷

It is important to note that there could be other explanations for why some hunter-gatherer societies like the Kitavan are less prone to acne. For example, it may have something to do with their diet and lifestyle.

Indeed, with all three of these theories about why humans may have evolved to have acne, we can only notice that certain phenomena seem to go together–such as loss of body hair and acne–but we cannot prove that one caused the other.

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