Stressful work and social occasions are often made much worse by what comes with them: sweat.
This type of sweat is different than the perspiration brought on by hot weather, which is intended to cool the body. The purpose of stress-triggered sweat mostly remains a mystery, but now scientists are piecing together new clues about the role it might play in the way people function.
Although most of us try to avoid sweating in public, some scientists believe it has an evolutionary role in sending warning signals to people around us. The body odor of a stranger provokes the brain to negatively interpret social stimuli, even friendly facial expressions, recent research has shown. Meanwhile, the scent of a family member can help calm a person who is under stress, according to a soon-to-be-presented study.
Women and men respond differently to signals sent by bodily smells such as sweat. When researchers tested some 40 different fragrances to see if they could cover up other people's body odor, they found that men were fooled the bulk of the time. But for women, the masking scents almost never lessened the intensity of the body odor.
"We concluded that body odor must be something special for women," says Charles Wysocki, a faculty member at Monell Chemical Senses Center, a scientific research institution in Philadelphia, and a co-author of the gender-based study. "The more I study this the more I'm amazed at how much information is being conveyed from one individual to another by their odor," he says. The research was published in Flavour and Fragrance Journal in 2009.
Most people devote a lot of effort trying not to sweat or smell from stressful situations. Americans spent $2.69 billion on deodorants and antiperspirants in 2011, up about 13% from five years earlier, according to market-research firm Euromonitor International.
Consumer products company Procter & Gamble has targeted women worried about stress-induced sweat with its recent "Stress Stinks" marketing campaign. The company said its patented odor-neutralizing technology, contained in its Secret Clinical Strength antiperspirant, was tested by researchers in Germany who used a clinical procedure involving public speaking and mental arithmetic to induce stress in women. The study results will be presented at the American Academy of Dermatology meeting in March, says Susan Biehle-Hulette, Procter & Gamble's senior scientist for product development.
Sweat from being overheated is produced by eccrine glands, which are located just under the skin all over the body. But sweat caused by stress, fear, anxiety and sexual arousal is produced in the apocrine glands, found only in certain areas, such as under the arms. In addition to water and salt, the main ingredients of heat sweat, stress sweat also contains fatty substances and proteins that readily interact with bacteria living on the skin to create what is commonly called body odor.
Choose Your Weapon
Two ways to fight the effects of stress sweat:
- Deodorants often contain a mild antimicrobial to make the skin less attractive to bacteria. Scents may help mask odor.
- Antiperspirants usually contain aluminum compounds that help block sweat pores and reduce sweat.
Stress sweat is triggered by the same hormones, mainly adrenaline, that prompt us to react quickly when faced with a threatening situation. "It's highly tied to the fight or flight response," says George Preti, a faculty member at Monell Center. Still, the purpose of sweating while under stress isn't clearly understood.
In a study published in the journal Social Cognitive and Affective Neuroscience in 2011, researchers found that exposure to another person's stress sweat sharpened alertness. "It enhanced the brain's perception across the board, not only to things that are obviously a threat but also to things that aren't obvious but might be threats," says Lilianne Mujica-Parodi, an associate professor of biomedical engineering at Stony Brook University in New York and lead author of the article.
Researchers collected sweat from 64 men during their first time skydiving and again while exercising. They then looked at the response of 14 other people while inhaling the different sweats. Those inhaling the stress sweat had a heightened brain response—measured by prefrontal cortex response using an EEG—-when looking at faces of all expressions, not just the threatening ones.
An earlier study conducted by Dr. Mujica-Parodi and other researchers found that the activity in the amygdala region of the brain, which processes emotions such as fear, was more active in people exposed to stress sweat rather than exercise sweat.
The study was published in the online journal PLOS ONE in 2009.
Johan Lundström, an associate member of the Monell Center, has conducted studies showing that when a person smells the body odor of a stranger the body's neural fear network gets activated, even when the person isn't aware of what they are smelling. Also at Monell Center, faculty member Pamela Dalton showed that stress levels decreased faster when people were exposed to the body odor of a family member rather than that of a stranger or a neutral fragrance.
The findings suggest that familiar and stranger body odors may be cues for emotional responses, Dr. Dalton says. The study, which involved 66 participants and was funded by the U.S. Army Research Office, will be presented at the Association of Chemoreception Sciences conference in April, she says.
Scientists are divided about whether underarm sweat—which includes apocrine and eccrine sweats, along with naturally occurring bacteria —contains compounds that may have a pheromone-like affect on humans. Pheromones are common in animals and insects to communicate sexual attraction and other messages and to trigger certain behaviors. But it's unclear if humans communicate through chemical methods.
Dr. Preti, of the Monell Center, believes such messages do exist. In a 2003 study he was involved with, 18 women exposed to the underarm odor of several men showed evidence of altered mood, including increased relaxation. Still, he says, it isn't clear which chemical compounds in sweat scent might account for the changes.
Stress and anxiety can intensify sweating disorders, but these typically involve excess activity by the eccrine gland, which is responsible for producing heat-related sweat. A common disorder, hyperhidrosis, which is estimated to affect as many as 3% of Americans, can occur in one area, such as the palms, or all over the body.
Possible treatments for hyperhidrosis include oral medications or prescription antiperspirants. Botox injections, which cost about $1,000 or more for both underarms and can last about six months, block neurotransmitters that stimulate the sweat glands. Serious complications from Botox use are rare though some patients can experience some bruising or temporary muscle weakness, says David Pariser, a Norfolk, Va., dermatologist.
Other treatments for very sweaty palms or feet include placing the appendage in water with a very low electric current. If done regularly, it temporarily prevents the nerves from producing sweat.
Michael May, a jewelry specialist at a New Orleans department store, says he worried that his underarm hyperhidrosis was affecting how customers perceived him. "My shirts were wet underneath and if I had to take my jacket off I'd have big wet marks underneath my jacket. I just couldn't handle it."
Mr. May, 32, two years ago started getting Botox treatments under his arms. It didn't completely eliminate the sweating but he says he now has it under control. "I just sweat like a normal person now," he says.
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