Human body odor formation is greatly affected by the structure and actions of human-associated microbial communities (1, 2, 3, 4, 5). In other words, the trillions of microorganisms that colonize your body greatly influence what you smell like. You have a unique body odor, in part because you have a unique microbiota, which is shaped by environmental forces, as well by your genetics.
Your body odor reveals a lot about your health. If you eat a species-appropriate, Paleolithic-type diet and harbor a diverse, healthy microbiota, then you probably smell pretty great. If you eat an unhealthy diet and/or your microbiome is in a sorry state, however, then chances are your body odor isn’t that pleasant. This is empowering, in the sense that it means that you have the ability to change the way you smell by changing the composition of your microbiome.
Olfaction: The least appreciated of the five major human senses?
Recent research suggests that hunter-gatherers are more in tune with their olfactory abilities and are better able to name different smells than humans living in industrialized nations (6). This makes sense, seeing as hunter-gatherers live in close contact with mother Earth and use their olfaction system for a variety of purposes in their daily lives. We – modernized humans – obviously also use our sense of smell as we navigate the world; however, we rely more on our visual abilities, as well as our hearing, in large part because we are so immersed in modern technology. For that reason, we often neglect the importance of olfaction.
From a Darwinian point of view, it makes complete sense that we possess a sense of smell. Our ability to detect different smells helps us safely navigate our environment. We find the smell of rotten food, decomposed animal tissues, and runny feces repulsive, because all of these things threaten our health and reproductive fitness. If we ingest them or otherwise come into contact with them, we may get sick.
What’s often forgotten is that these principles also apply to our interactions with living organisms. We find healthy people and animals more attractive than sick ones (7). This makes sense, seeing as sick organisms are a source of pathogens, whereas healthy ones are more dominated by friendly bacteria. Not only that, but throughout human evolution, it’s undoubtedly been more beneficial to have “healthy allies” and partners than unhealthy ones, seeing as the former stand a better chance of getting a hold of food, producing and raising healthy offspring, and warding off potentially deadly infections, among other things.
This is one of the things we do with our senses: we assess the health and reproductive capabilities of others. Our sense of smell not only helps us determine whether the people and animals we come across harbor healthy microbial communities or not; it also shapes our mate seeking behavior. Animals are attracted to other animals that possess an immune system and microbiota that match well with their own, in a Darwinian sense (8, 9, 10, 11, 12, 13).
All of this is to say that how you smell significantly affects how you interact with the world. Your body odor doesn’t just provide you with information about how your body is functioning; it also affects how attractive you are to others.
Your microbiota produces a variety of odor-emitting compounds
The microorganisms you harbor shape your gene expression pattern and many of the physiological processes of your body. They break down various compounds (e.g., nutrients, toxins) that you ingest, breathe in, put on your skin, and produce. The microbes don’t just magically make these compounds disappear; rather, they turn them into other substances, some of which may ultimately contribute to shaping your body odor.
This helps elucidate many smelly phenomenons. For example, it helps explain why we give off a distinct smell when we exercise. Compounds in sweat are broken down by some skin bacteria, a process that results in the generation of the stereotypical gym smell.
Here’s what the authors of a 2011 review paper had to say about this matter:
It is now generally accepted that skin bacteria cause body odour by biotransformation of sweat components secreted in the human axillae. Especially, aerobic corynebacteria have been shown to contribute strongly to axillary malodour, whereas other human skin residents seem to have little influence. Analysis of odoriferous sweat components has shown that the major odour-causing substances in human sweat include steroid derivatives, short volatile branched-chain fatty acids and sulphanylalkanols. (1)
What’s important to point out is that it’s not just the bacteria that are found on your skin that affect what you smell like; organisms that are found many other places in and on your body do as well. Oral microbes, for example, greatly influence the smell of your breath. If you eat a diet low in sugar, don’t smoke, and regularly clean your teeth, then your breath is probably pretty good; however, if that’s not the case, then smelly microbes may have been able to take over control of your mouth.
A healthy microbiota: The best perfume there is?
In developed countries, it’s extremely common for both men and women to use deodorant and perfume, as well as various chemical-laden oral care products. Many women in particular completely immerse themselves in fragrance, in an attempt to smell great and cover any possible malodor.
One of the main reasons we’ve become so reliant on these products is that many of us eat an unhealthy diet and harbor species-depleted, pathogen-rich microbial communities. A healthy microbiota may actually be a much better form of perfume than cologne. It obviously won’t make you smell like a pleasantly perfumed Hugo Boss model; however, it will give you a fairly neutral body odor and act as a safeguard against body malodor.
A person who harbors a healthy microbiota may not smell like fresh peaches following an intense bout of exercise, however, he/she will undoubtedly smell a lot better than someone whose microbiota is in a less than optimal state. This statement is based on my own experience, things I’ve observed over the years, and recent research which indicates that microbiota composition is an important determinant of body odor characteristics (2, 4).
Cosmetics and beauty products are today so integral to many people’s lives that it’s often forgotten that it’s only very recently that it became normal for members of Homo sapiens to use skin lotions, deodorant, perfume, and the like. Many assume that “cavemen” smelled really bad; however, this assumption has to my knowledge no scientific/evolutionary basis.
I actually find it extremely unlikely that our primal ancestors smelled bad. I would go as far as to say that I think they smelled a lot better than most contemporary humans do, despite the fact that they didn’t shower every morning or use soap or shampoo. The reason I hold this belief is that our primal forebears ate a very healthy diet, harbored diverse and resilient microbial communities, and were generally very fit. Moreover, seeing as we’re attracted to people who smell well, it seems highly probable that Darwinian selection has historically favored humans that give off a scent that is pleasant to others. This scent wouldn’t necessarily be highly attractive to everyone, but it certainly wouldn’t be off-putting. Personally, I’ve found that I smell a lot better at times when I feel my microbiota is in good shape and my body is working well than during periods when that’s not the case.
The fairly recent recognition that microbes are intricately involved in shaping how we smell has triggered some scientist to suggest that friendly bacteria may be our best weapon against body malodor (2, 4). Some have gone as far as to suggest that bacterial transplants and probiotics could be the ultimate deodorant (2).
The bottom line
Your body odor is largely shaped by your genetics, as well as by your microbiota. Of these two things, the one you have the most control over is your microbiota. Your unique microbiota expresses a unique scent via the compounds it produces.
A healthy, diverse microbiota gives off a very different scent than an unhealthy, pathogen-rich one. We find the former scent more pleasing and attractive than the latter; probably because it’s better, from a Darwinian point of view, to socialize and mate with healthy individuals than unhealthy ones.
Instead of completely covering your body in perfume before you head off to work in the morning, you are probably much better off focusing on enhancing the diversity and health of your microbiota, for example by increasing your intake of fiber, eliminating processed foods from your diet, reducing your use of cosmetics and soap, and increasing your intake of friendly bacteria found in traditionally fermented foods.