By Amanda MacMillan
January 9, 2018

A new study lends some scientific backing to anyone who’s ever worn their partner’s shirt or slept on their side of the bed when they weren’t around: According to research published in the Journal of Personality and Social Psychology, the scent of a romantic partner can help lower stress levels, even in his or her physical absence.

The scent of a stranger, on the other hand, raised stress-hormone levels in the study—an unexpected finding, say the authors, but one that does make evolutionary sense.

Previous research has shown that the presence of a romantic partner can lower stress levels, but scientists at the University of British Columbia in Canada wanted to see if their scent alone could do the same thing. They recruited 96 heterosexual couples and asked the men to wear a clean T-shirt for 24 hours, without using deodorant or scented body products, smoking or eating certain foods that could affect their natural scent.

Men were chosen to provide clothing samples because they tend to produce more scent, says lead author Marlise Hofer, a PhD student in the department of psychology. Women, meanwhile, have a naturally better sense of smell. After the shirts were worn for 24 hours, they were frozen to preserve any scents that were left behind.

MORE: Does Smell Dating Actually Work?

The women in the study were then asked to smell a T-shirt that had either been unworn, worn by their partner or worn by another man they did not know. Immediately afterward, they were given a mock job interview and a difficult mental math exam designed to evoke stressful emotions. They also answered questions about their stress levels and provided saliva samples to measure levels of cortisol, a stress hormone.

Women who had smelled their partner’s shirt reported feeling less stress both before and after their interview and exam, compared to those who had smelled an unworn shirt or a stranger’s shirt. Those who were able to recognize their partner’s scent also had lower cortisol levels than other women in the study, suggesting that the stress-relieving benefits may be greatest when a person is aware of what they’re sniffing.

Women who smelled a stranger’s scent, on the other hand, had higher levels of cortisol before and after their stress tests. “Humans have developed to fear strangers, especially strange males,” says Hofer. “It’s possible that a strange male scent triggers the fight or flight response, even without us realizing it.”

Hofer says she and her co-authors would like to study the connection between scent and stress in other ways, including whether men would have the same reaction to a romantic partner’s scent. A man may be less likely to wear his girlfriend’s shirt while she’s away, says Hofer, but he may still sleep on her side of the bed or smell other items that belong to her.

“I know I’ve personally seen men smelling the hair of their partner when they’re standing behind them,” she says, “so maybe they just have slightly different behaviors that are accomplishing basically the same thing.”

It’s not yet clear whether the smell of certain products—like perfume, shampoo or men’s body spray—would trigger similar stress reductions in romantic partners. “We’d have to do more research to see if people exposed to familiar scents they associate with their partner have the same response,” says Hofer, “or if this is something unique to our natural body odors.”

The researchers say that their findings could suggest an easy way to lower stress levels when traveling or taking on solo challenges: Take an article of your partner’s clothing along. They’re also interested in studying scent-and-stress connections between parents and children.

“Being separated from young kids can be very stressful for both parties,” says Hofer. “If we can make it easier to leave your child at daycare for the first time or train them to sleep through the night without you, this could have very practical implications.”

Contact us at editors@time.com.

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