The Science of Sweat, Smells, and the Skin Microbiome

The Seed Digest:

• Everyone sweats, but how much you produce depends on factors like your age, environment, and emotional state.
• Sweat-related body odor develops when the bacteria of your skin microbiome metabolize sweat and create fragrant compounds in the process.
• Switching up your antiperspirant use and bathing routine can help support your skin microbiome while keeping BO in check.

What compound is constantly protecting you from pathogens, regulating your body temperature, and keeping your skin moisturized? Yep, sweat does all this and more—all while nourishing your all-important skin microbiome.  

Let’s dig deep into the science of sweat (and its associated scents) and learn why the stuff we spend so much time hiding is actually liquid gold. 

What’s in Your Sweat?

Sweat is 99% water, but it also contains small amounts of electrolytes, including sodium and chloride (ions that create that salty taste and play a crucial role in fluid balance) and potassium (which supports normal cell function). Traces of metabolic waste products, lactate, glucose, minerals, amino acids, and antimicrobial peptides can also be found in each droplet.^1,2,3

Most of this sweat escapes your body via roughly two to four million eccrine sweat glands.² This is the main type of sweat gland that’s active starting at birth and is largely responsible for thermoregulation.^2,4 (As sweat evaporates from the skin’s surface, it releases heat to reduce your body temperature.)⁵ Fun fact: Your body is always secreting sweat. It may just be too little to notice until the body starts to heat up and sweat gland activity increases.⁶

Beyond helping us cool down, sweat contains antimicrobial peptides that fend off pathogens on its way out, reducing the risk of skin infections.² It also helps maintain the acid mantle (a thin protective layer of the skin’s surface that limits the growth of harmful microorganisms) and keeps skin moisturized and hydrated.^2,7

In general, the parts of your body that have the highest concentration of sweat glands tend to be the sweatiest. The palms of your hands and soles of your feet are packed with eccrine sweat glands (roughly 250 to 700 glands per square centimeter). The head, forearms, and back also have a high proportion of sweat glands and are common perspiration producers too.^2,4,6,8 

The Bacteria Behind BO

Sweat is often associated with strong stenches that make your nose wrinkle. But in reality, sweat itself doesn’t smell.⁹ What gives? 

Your skin microbiome has a lot to do with it. Reminder: The skin microbiome is the collection of more than 600 species of bacteria, fungi, and viruses that reside on and in the three main layers of human skin (epidermis, dermis, and hypodermis). As you break a sweat, some of these bacteria break down the components of the perspiration. In the process, these microbes produce smelly volatile organic compounds (VOCs) like volatile fatty acids and thioalcohols.^10,11 Hello, body odor.

One common bacterium behind BO is Corynebacterium, which produces certain smelly volatile fatty acids as it metabolizes sweat.^9,11 The more of this bacterium living on your skin, the more body odor you’ll likely have.¹⁰ Meanwhile, the Staphylococcus epidermidis living on your feet can degrade the leucine in your sweat into the foul compound isovaleric acid.¹² And the Staphylococcus hominis in your armpits produces pungent sulfur-containing thioalcohols.¹³ 

Your sweat tends to smell when it pools out of apocrine sweat glands—a second type of sweat gland located in areas such as the armpits, chest, face, scalp, and genitals. These glands become active during puberty and are associated with hair follicles, home to sebaceous glands that secrete oily sebum.² 

Interestingly, the skin microbiome can also affect your sweat’s color, though this is rare. In the case of the condition chromhidrosis or pseudochromhidrosis, sweat can become yellow, green, blue, or black due to a build-up of a pigment in the sweat glands, potentially triggered by certain drugs that alter the microflora on the skin surface.^14,15 

Why Some People Sweat More Than Others

No two people produce the same amount of sweat. Your personal output in any given moment depends on your sweat glands, the temperature and humidity of your environment, your activity level, hormones, health conditions, medications, and more. 

Age and weight may also influence your sweat production. Older adults have been found to produce less sweat per gland than younger adults, and folks with higher body mass may have higher sweat rates.² Then there’s genetics. For example, a mutation of the ABCC11 gene, common in East Asian populations, causes sweat to remain trapped inside cells where bacteria can’t break it down. People with this mutation have little or no body odor.¹⁶

Your emotional state can make or break your sweat and smell status, too. During times of emotional stress (such as anxiety, fear, or excitement), the body activates the sympathetic nervous system, which in turn stimulates apocrine sweat glands.⁸ Upon activation, apocrine glands secrete a thick, milky fluid rich in proteins and lipids.² This secretion, while initially odorless, can develop a noticeable, distinct smell upon interaction with skin bacteria.

There’s a dose-response relationship between stress intensity and stress sweating, so the greater the stress, the greater the sweat.¹⁷ No wonder the blazer you wore to a job interview needs a dry cleaning.

Since the composition of the skin microbiome is such a strong driver of body odor, some researchers are now investigating whether applying probiotics (non-odor-causing bacteria) to the skin can help subdue stench. An armpit bacterial transplantation—which removed the armpit microbiome from a person with BO and replaced it with bacteria from the armpit microbiome of a donor without BO—has even been completed, though this procedure still needs to be validated before it goes mainstream.¹⁰

Don’t Sweat It

Sweating is a normal and essential bodily function, and it’s nothing to be ashamed of. That said, there are a few ways to help support your skin microbiome that may also keep perspiration and BO in check.

Cleanse well, but not too often. 

Cleaning the skin is a balancing act. Doing so too often can strip the skin of lipids and moisture, potentially leading to irritation, skin barrier impairments, and microbiome disturbances.¹⁸ But prolonged periods without showering can allow populations of bacteria, fungi, and other microbes to grow and skin cells to build up—an accumulation that may lead to body odor and skin conditions like acne and (more rare) dermatitis neglecta.¹⁹ 

Your game plan: Shower after sweating to shed any compounds that can contribute to bacterial overgrowth and acne. Make sure to use a gentle, non-antimicrobial cleanser and avoid water that’s too hot in order to maintain the skin’s natural oils and prevent disruptions of the skin microbiome.

Don’t go overboard on antiperspirants or deodorants. 

Antiperspirants minimize your sweat production (and, in turn, smells) by plugging sweat glands with ingredients like aluminum chloride. Deodorants use fragrance to offset your body odor. Often, these two products also contain antimicrobials that shift the skin microbiome and curb the growth of stink-inducing bacteria.²⁰ 

That said, overusing deodorants and antiperspirants may lower the microbial density of the skin microbiome, opening up space for new (and potentially pathogenic or odor-producing) bacterial species to take hold.^8,21 Apply these products sparingly, and chat with your healthcare provider or dermatologist if you’re looking for specific recommendations.

Chat with your healthcare provider. 

Some folks may experience excessive sweating due to the overstimulation of certain receptors on eccrine glands, a disorder known as hyperhidrosis. The condition affects roughly 3% of the US population. If you’re sweating excessively from the eccrine glands (usually the palms, soles, face, and head), and your symptoms have lasted longer than six months, speak with your healthcare provider for a personalized treatment plan.²² 

Frequently Asked Questions (FAQs)

• How do you keep your skin microbiome healthy? In general, using gentle, non-antimicrobial cleansers, minimizing stress, spending time outdoors, and eating a plant-rich diet can support the health of your skin microbiome. For more details, check out our Skin Microbiome 101 guide.
• Why causes BO to be stronger than usual? Body odor may smell stronger if your skin microbiome contains more of the specific bacteria that break sweat down into smelly volatile organic compounds. 
• Does sweating improve skin health? Yes! Eccrine sweat glands secrete moisturizing compounds (like lactate, urea, sodium, and potassium) that help maintain skin hydration, as well as antimicrobial peptides that fight skin infections and control skin flora.³ 

The Key Insight

Perspiration is nothing to sweat about: It has many benefits for your health. Your sweat (and associated smells) are a reminder of your body’s incredible ability to self-regulate. So let’s add sweating to the ranks of farting and pooping and make it something to celebrate rather than hide.