The body has a number of regulatory mechanisms designed to keep us safe and healthy. There is a complex series of physiological processes that takes place when we eat, sleep, breathe, and move throughout our day that keeps the body functioning properly. Sweating, or perspiration, is one way the body maintains this equilibrium despite changes in the environment. We sweat on a hot, sunny day or during a cycling class to keep our core body temperature within a certain range.
However, the utility of sweating extends beyond thermoregulation. Sweat can assist in detoxification processes and can even aid in our ability to communicate with others. It can also be used as a diagnostic tool. A sweat test measuring chloride concentrations can screen for cystic fibrosis. There is research on the use of sweating as a less invasive alternative to blood for measuring a variety of health biomarkers, although clinical applications are currently limited.
There are three types of sweat glands in the human body: apocrine, apocrine, and eccrine. Eccrine glands produce sweat that is mostly water and electrolytes. Apocrine and apocrine glands develop from eccrine glands before and after puberty, respectively. Apocrine glands are larger and produce sweat that contains other components besides salt water, such as ammonia, protein, and lipids. This sweat is largely the reason that there are countless deodorant and antiperspirant products on the market. Apocrine sweat interacts with bacteria on the skin, which causes odor.
When we sweat, heat is transferred from the body to the skin, and evaporation cools us down. While thermoregulation is vital for maintaining homeostasis, some heat stress may be beneficial for our health. There is a long history across cultures of sauna use, and research is finding a connection between sauna therapy and reduced mortality risk. Acute heat exposure can upregulate the expression of heat shock proteins as well as nuclear factor erythroid 2-related factor 2 (Nrf2), which are involved in cellular and antioxidant regulation. Sauna use has been associated with a decreased risk of neurodegenerative disease such as Alzheimer’s disease. The Kuopio Ischemic Heart Disease (KIHD) study demonstrated a dose-dependent inverse correlation between sauna use and the risk of cardiovascular disease fatality. This finding may be due to a decrease in blood pressure, as well as an increase in heart rate. Circulation increases as blood moves from the core toward the skin to aid in sweat induction.
Exercise and Sweating
Sweating is also instrumental for regulating core body temperature during exercise. Studies have shown that sweat production is enhanced through regular exercise due to changes in factors such as gland size and output. This change improves an individual’s ability to exercise for longer periods of time without overheating. A study of trained runners and sedentary individuals showed that the time of sweat onset was shorter for the runners, and they also experienced 34-46% greater sweat rates compared to controls when all participants engaged in a cycling protocol. VO2max, which is used to assess cardiovascular fitness, was higher for the runners and correlated with sweat rate and onset. This response was not seen in controls.
Interestingly, different kinds of sunscreens can impact sweat production. While more research is needed on the specific ingredients that may be responsible for this effect, this could have implications for thermoregulation during outdoor exercise.
Sweating serves as an important modality for detoxification. Activities such as sauna therapy and exercise have been included in detoxification protocols for military personnel, law enforcement, and workers exposed to occupational hazards.
A four to six-week detoxification protocol involving exercise, sauna therapy, and nutritional supplementation was used to support veterans suffering from Gulf War Illness (GWI). Participants were experiencing a number of symptoms including chronic pain, insomnia, and fatigue prior to the program but noted improvements in pain, mental health, and general health afterwards. In fact, 50% of participants no longer met the Kansas criteria for Gulf War Illness after completing the program. Gamma-glutamyl transpeptidase (GGT), a biomarker that can be used to assess toxic burden, was mildly decreased and remained lower 3 months after the protocol.
Police Officers and Firefighters
A separate study used the same protocol to support police officers who were involved in the investigations of methamphetamine drug labs. Study participants had statistically significant positive changes in all sections of a health survey after the conclusion of the program. Symptom severity scores were also significantly lower for a variety of different categories such as cognition, immunity, musculoskeletal, and neurological. As 96% of participants reported troubles with insomnia prior to treatment, perhaps one of the most impressive results was an increase in sleep from 5.8 hours per night to an average of 7.6 hours per night. Participants also reported an average of 9.3 days per month of poor physical health prior to the protocol and 1.8 days at the end.
Given that a variety of toxicants are now ubiquitous in our environment, modalities that induce sweating can be valuable for many people and not just those who may have been acutely exposed. Researchers analyzed the efficacy of sweating as a method of excretion for a variety of different toxicants through the Blood, Urine, and Sweat (BUS) study. Polybrominated diphenyl ether flame retardants, which can be found in plastics, polyurethane foam, construction materials, and household dust, are a source of persistent organic pollutants (POPs). These can accumulate over time in the body through continuous, low-grade exposure. Investigators reported that these flame retardants were not excreted in urine. However, five congeners were excreted through sweat.
The same group of study participants were also tested for levels for bisphenol A, or BPA, which is found in cash register receipts, plastic food containers, and the lining of canned foods. Researchers found BPA in the sweat samples of 16 out of 20 participants, even though they did not find BPA in the blood or urine of some individuals. This demonstrates the importance of using sweating as a method to measure toxic burden since using only blood or urine could paint an inaccurate picture of total BPA levels.
Phthalates are another toxicant found in plastics, but they are also used in nail polish, shower curtains, and vinyl flooring, among other things. Some metabolites of phthalates are excreted in sweat while not being found in blood, again pointing to the value of sweat for both elimination and assessment. The sweat concentration of mono-2-ethylhexyl phthalate, a phthalate metabolite, was two times that of urine levels in the BUS study. Finally, some subtypes of polychlorinated biphenyls (PCBs) were found in sweat. Although PCBs have been banned, they still persist in the environment and can bioaccumulate.
Heavy Metals and Sweating
Sweat can also induce the excretion of metals. A study of the effects of exercise on iron levels in athletes showed that there was a significant increase of iron found in sweat after 4 weeks. This may have important implications for athletes who are experiencing iron deficiency and anemia. On the other hand, studies have shown that heavy metals such as cadmium, lead, arsenic, and mercury can also be excreted through sweat. In fact, arsenic can accumulate in the skin, and cadmium has been found to be more concentrated in sweat as compared to blood.
While the benefits of sweating for temperature regulation and detoxification are more well-known, there is an interesting body of research on the use of sweat as a mode of communication. So much of communication is nonverbal, and this could extend to perspiration. We’ve all heard the phase “don’t sweat the small stuff” when it comes to experiencing stress and worry. It turns out that feelings of happiness and fear not only influence sweat production, but these emotions can also be perceived by others due to volatiles in the sweat. Men are frequently used in studies of chemo signals in sweat because they have larger apocrine glands. Women are often the chemo signal receiver in studies because they are generally thought to have a better sense of smell as well an enhanced ability to perceive emotions compared to men.
Several studies from the last few years demonstrated that men who watched clips from horror movies not only experienced an increase in heart and respiratory rates as well as salivary cortisol, but they produced more armpits sweat compared to when they watched a nature documentary. A stronger fear response to the movie clips was also correlated with more odorous volatiles from apocrine sweat glands.
Physiologically, these chemo signals are thought to help promote safety within groups because individuals who were previously unaware of potential danger will receive a signal to remain vigilant. Female university students were asked to play a computer game and were instructed to press the escape key when they noticed a change in the game. As they played, they were exposed to fear chemo signals from male sweat. While women didn’t report an increase in perceived stress, they pressed the escape key significantly faster when they were exposed to fear sweat compared to neutral sweat. This quicker reaction time may be indicative of heightened readiness to respond to stimuli.
In studies on emotional chemo signals, facial muscles used to express fear are activated when women are exposed to sweat from males who watched the scary movie clips. A randomized, double-blind, placebo-controlled study used sweat from stressed men compared to men undergoing exercise training. Both male and female participants were exposed to these sweat samples while engaging in an emotional face recognition test. Some participants also received intranasal oxytocin, which is a helpful hormone for modulating the stress response. Participants experienced greater activity in the amygdala and anterior cingulate cortex when exposed to stress sweat compared to exercise sweat. These parts of the brain play a role in emotional processing.
During the recognition test, women perceived ambiguous facial expressions as being fearful and also responded more quickly to medium and high-level fearful facial expressions when exposed to the stress sweat. However, this fear recognition pattern was reversed in those who were given exogenous oxytocin. Men responded more quickly to high-level fearful expressions while exposed to stress sweat, and this was also reversed with oxytocin. This study not only shows that women may pick up on greater subtleties in facial emotional expression, but also that we engage other bodily systems besides the olfactory system in order to process emotions conveyed through sweat.
Genetics and Sweating
Although genetics can impact sweat gland activity, chemo signals are nevertheless recognized across cultures and ethnicities. One of the previously discussed studies demonstrated that women from Portugal and the Netherlands experienced the same facial activations when exposed to stress sweat. A separate study of Chinese and Dutch females showed that sweat samples from happy donors increased the speed at which females were able to recognize happy faces during a facial expression recognition test. Exposure to fear samples increased facial recognition regardless of the expression, indicating an increase in vigilance in both Chinese and Dutch participants.
Effects of Deodorants
Deodorants and antiperspirants are designed to reduce body odor, and in doing so, they impact bacteria on the skin. However, it’s interesting to consider how a disruption of the skin microbiome could impact our chemical communication with others since sweat volatiles would be disrupted. In some situations, such as networking events or when we are giving a big presentation, this could be beneficial as our fear or anxiety might be more concealed. However, there are other instances in which experiencing shared emotions (such as happiness) could promote a sense of connection.
- Sweating can cause a loss of fluids and electrolytes, making it imperative to hydrate properly when engaging in sauna therapy or exercise.
- Sweat rate can vary between individuals. The concentration of electrolytes found in sweat can be impacted by diet, genetics, activity level, and even seasons of the year, making it important to personalize hydration strategies.
- Saunas are not right for everyone, and it is recommended to speak with your qualified health professional prior to engaging in sauna therapy.
- Sweat can be an important excretion route for a variety of toxicants and may be strategically induced during detoxification protocols.
- Increased toxic burden can impact the autonomic nervous system, which may impede an individual’s ability to sweat. Personalized diet and lifestyle interventions can support detoxification processes and may be useful prior to or during a protocol involving sauna or exercise.
- We are able to communicate with so much more than words, and the more subtle modes of communication can help to create a shared sense of emotional experience.
If you plan to incorporate exercise or sauna bathing or have allergies or questions about which foods or sweating activities can best support your mood and health goals, talk to your doctor, nutritionist, dietician, or another member of your healthcare team for personal options based on your individual circumstances.