Hot Sweat vs. Cold Sweat—What’s the Difference?

Sweat can get a bad rap, but it is a normal function that keeps the body cool and acts as a subtle—and sometimes not so subtle—way of communication. Not all sweat is created equal, though. There are two main types of sweat glands which produce sweat with distinct characteristics. To better understand these, scientists are investigating the small stuff: the chemical signals present in sweat, the microbes that contribute to body odor, and how sweat is a social cue to others.

The Body is a Sweat Wonderland

When jogging at the gym or being outside in the sweltering heat, eccrine glands release sweat, which evaporates off the skin and helps the body cool down when its internal temperature rises. These glands are widely distributed throughout the body with the highest density on the palms of the hands, soles of the feet, and on the scalp. This sweat is primarily comprised of water and some electrolytes like sodium and chloride; because of this, sweat tends to be odorless.

Unlike eccrine glands, apocrine glands release a thicker, oilier sweat into the hair follicles in response to emotional changes—stress, anxiety, or even an adrenaline high. The apocrine glands are found in the armpits and other areas that are abundant with hair follicles, such as the genital regions.

Sweat from apocrine glands contains higher concentrations of proteins and lipids, making it a rich feast for microbes.¹ “The bacteria on the skin start processing these [molecules] that produce odor,” said Monique Smeets, a social cognitive psychologist at Utrecht University who is interested in the social significance of sweat and body odor as a medium of social communication. “Isovaleric acid is the typical gym locker smell that is produced.”

Apocrine glands are primarily associated with body odor, as this type of sweat is packed with different chemical precursors. Bacteria break these down into other distinct odors, like the pungent scent of 3-methyl-2-hexenoic acid, which is often associated with stress.

“It has been posited that apocrine sweat glands would be involved in the release of [chemosignals]. It’s more to communicate to other people who you are, how you’re doing, like whether you’re sick or stressed,” explained Smeets.

Researchers like Smeets focus on odor precursors and smelly molecules from both a chemical and sensory perspective. These tiny molecules might seem insignificant, but they tell a much bigger story about the states and traits of an individual.

Sweatprints: How Sweat’s Molecules Reflect Emotional States

There are many questions revolving around sweat: What is the chemical composition of different types of sweat, and can people smell the difference between these?

Smell is a powerful sense that shapes people’s perception of the world.^2,3 While some body odors—like those after an intense gym session—might make people’s noses wrinkle, researchers have delved into how body odor isn't just a byproduct of the body’s functions; it is a form of communication, known as chemosignaling. For example, people can experience a cold sweat when faced with emotional stress, anxiety, or fear. But it’s not just stress—hormonal changes such as puberty or sexual arousal can also trigger these responses.

In one study, scientists sought to determine whether fear intensity could be encoded in sweat.⁴ Participants watched frightening videos, and researchers measured the amount of sweat produced as well as the number of volatile molecules released. The study found that participants who experienced stronger fear not only perspired more but also emitted a distinct “fear smell” through the composition of volatile compounds. In a follow-up study, the researchers explored whether this fear sweat could influence others’ physiological, behavioral, and neural responses.⁵ Sure enough, the results suggested that receivers could partially inherit the sender’s fearful state, depending on the intensity of the scent.

Smeets and her colleagues took this a step further, investigating whether the volatile chemicals in underarm sweat varied across different emotional states.⁶ They collected sweat samples from male volunteers—since men tend to sweat more and have a stronger body odor—in states of fear, happiness, and neutrality.

Then, the team conducted chemical analysis with gas chromatography-mass spectrometry. Fearful sweat was distinct from neutral sweat, with happy sweat having both differences and some overlap with other emotional states. Of these, Smeets noted that they identified candidate chemical classes associated with emotional and neutral sweat, specifically, linear aldehydes, ketones, esters, and cyclic molecules.

“We're making progress, but much more is needed. There may be a ton of other compounds producing the same effects that we haven't identified, or a combination of those that are more effective than just a single one,” said Smeets, who also noted that some scientists believe a few key volatile compounds are responsible for body odor, but their proportions play a crucial role. She added that the social context between individuals may also finetune this situation of cognitively processing chemical inputs and linking it to known information and previous experience to make sense of a situation.

How Diet, Genes, and Bacteria Shape Body Odor

These chemical components aren’t the only factors shaping sweat and body odor—many intrinsic and extrinsic elements also come into play. According to Smeets, factors like sex, age, personality (including self-esteem levels), health status, diet, and even product usage (such as deodorant or fragrances) contribute to how body odor develops.

For instance, one study revealed that women rated the body odor of men with high self-esteem as more pleasant and less intense than that of their low self-esteem counterparts.⁷ This highlights how psychological factors can influence body odor and how it is perceived. Additionally, many people may have noticed how their sweat odor changes after eating foods like garlic or meat, which are high in sulfur. These foods can lead to more intense and sometimes unpleasant body odors.

Beyond diet and emotional state, there’s a genetic component that can impact body odor. In 2006, researchers found that the ATP binding cassette subfamily C member 11 (ABCC11) gene plays a critical role in sweat production.⁸ It creates a protein that transports protein- and lipid-rich molecules to the skin, providing food for bacteria that results in the release of volatile compounds that cause body odor.

However, in individuals with inactive ABCC11, sweat molecules are unable to reach the skin, reducing bacterial activity and significantly lowering body odor. This gene also affects the microbial communities living on the skin.⁸ People with functional ABCC11 tend to have higher levels of Corynebacterium, which has been linked to more unpleasant and sulfurous odors. Meanwhile, those with an inactive version of the gene can have more Staphylococcus, which produces more neutral smells. Other microbes can mix things up and contribute their unique scents.

It turns out that when it comes to sweat, the most microscopic details matter. Not only does sweat keep the body cool but it also serves as a way of unconsciously sharing chemical signals. Smeets noted that scent matters and understanding the interplay between the molecules and microbes could better reveal how people communicate without words.