A study discovered that single men can smell different than men in committed relationships. As strange as this sounds, body smells could reveal a lot about a person. For instance, cholera gives off a sweet scent while acute diabetes can smell like rotten apples. Also, men find women’s body odor less pleasant during menstruation and more pleasant during the most fertile phase in the menstrual cycle. Body odor plays an understated role in human attraction, which may explain why women in this study were able to sniff out unattached men.
Single Men Have a Stronger Scent Than Partnered Men
Previous studies showed that single men tend to have higher levels of testosterone than men with partners, whose levels tend to decline. Research has indicated that testosterone contributes to body odor, which suggests that single men may have a stronger scent. Perhaps the smell is meant to biologically signal availability to women.
“Stronger body odor might help you stand out more. It might signal dominance,” said Mehmet Mahmut, one of the study’s authors. “Testosterone is associated with mate-seeking behaviors. We know from previous research that higher testosterone is linked to stronger body odor… Potentially single men do have higher levels of testosterone.“
To test this, the study authors gave plain white T-shirts to 91 men — 46 single and 45 partnered — and told them to wear them for an entire day. They added that the participants should do some moderate exercise to make sure “a significant amount of sweat was absorbed onto the underarm of the T-shirt.” 
Then the authors presented the sweaty shirts to 82 heterosexual women, who had to sniff each one and look at a photo of the man who wore it. They then rated the odor and the appearance of the men based on attractiveness, intelligence, sexiness, loyalty, trustworthiness, kindness, masculinity, and if they look like a good romantic partner. The more appealing the smell of the shirt, the women were more likely to consider their photos appealing. 
“Consistent with our hypothesis, single men’s BO was rated as smelling stronger than the BO of partnered men,” write the study authors. “We also found that single men’s faces were rated as more masculine than partnered men’s faces, but only among partnered women.”
Reasons Why Single Men Have Higher Testosterone
The researchers explain that scent can play a large part in romantic pairing. “From an evolutionary perspective, it may be advantageous for women to be able to detect the chemosignals that connote coupledom and ultimately avoid courting partnered males (especially with offspring) due to the relatively reduced resources they can offer.” 
Although a strong scent could indicate availability, it doesn’t necessarily make the male more attractive to potential partners. During the study, the women didn’t rate the smell of single men’s shirts to be more attractive than the other shirts. Interestingly, women in committed relationships described the faces of partnered men as looking more loyal and trustworthy than the single men; meanwhile, single women didn’t distinguish these traits in either types of men.
Biology aside, the authors provide another explanation for single men having stronger body odour. People without a partner may tend to let their hygiene slide. “Evidence for this assertion comes from research showing single men have poorer physical and mental health outcomes than partnered men which may manifest as poorer hygiene and therefore BO,” they write.
There may also be a demographic reason for higher testosterone in bachelors, simply that the hormone decreases with age and older men are more likely to be in committed relationships. Perhaps there is no one answer but a combination of several.
The Role of Scent in Romance
Mahmut hopes that this research would shed more light on the science of human attraction. “Being attracted to a partner…it’s the basis of life,” he said. “A basic part of being human is forming connections with other people. A life partner is one of the most important connections you will make.” 
Despite the interesting study, it doesn’t offer much practically. As Mahmut admits, “The usefulness of scent has somewhat decreased. We spent tens of thousands of years disguising what we smell like.” But a study by Ilona Croy at the University of Dresden, Germany, indicates that those with congenital anosmia (the loss of sense of smell) have poorer relationship outcomes. So while real-life interactions are too complex to rely on scent, it still plays a larger role in romance than previously thought. 
- “Do Single Men Smell and Look Different to Partnered Men?” Frontier Psychology. Mehmet K. Mahmut and Richard J. Stevenson. February 13, 2019
- “Experiments Show Women Can Sniff Out Single And Married Men.” Science Alert. Carly Cassella. December 27, 2022.
- “Women Can Smell If A Man Is Single.” IFL Science. Ben Taub. December 27, 2022
- “Single People Smell Different, According to Science.” News Week. Pandora Dewan. October 14, 2022
- “Why single people smell different.” BBC. William Park. June 22, 2021