Thursday April 16 2015
Can emotions be spread by chemosignalling?
"Humans can smell when other people are happy, researchers discover," The Independent reports; somewhat over-enthusiastically.
In a new study, Dutch researchers investigated where happiness could be "spread" to others, via body odours, through a process known as "chemosignalling".
Nine men provided sweat specimens during three sessions that aimed to make them feel happy, fearful or neutral. Film and TV clips were used to induce these feelings.
Thirty-five female students were then asked to smell the samples and their reactions were captured.
The women were more likely to have a happy facial muscle response if the sample was taken while the men watched happy clips. A fearful response was more likely if the sample was taken in the fear condition. Women seemed to be able to tell if the sweat had come from men in the happy or fearful condition compared to the neutral condition, but not from each other.
It is not possible from such a small study to be able to say with certainty that any changes were due to the smell.
The hypothesis that emotions could be spread via odours may be plausible to anyone who has been in a sweaty mosh-pit, rave, or the middle-aged equivalent, a post-wedding disco.
But while interesting, this study does not prove that body odours can transmit happy or sad feelings to others.
Where did the story come from?
The study was carried out by researchers from Utrecht University in the Netherlands, Koç University in Turkey, the Institute of Psychology in Lisbon and Unilever research institutes in the UK and Netherlands. It was funded by Unilever, the Netherlands Organisation for Scientific Research and the Portuguese Foundation for Science and Technology. (We seriously hope Unilever are not considering bringing any sweat-based products to market).
The study was published in the peer-reviewed medical journal Psychological Science.
The UK media reported the research accurately in terms of the actual story, though it seems some headline writers went out on a limb. For example, The Daily Telegraph’s headline "You can actually smell joy", while a delightful prospect, is unproven.
Also, the media did not explain any of the limitations in the study design.
What kind of research was this?
This was an experimental study of the effect of body odours in transferring human emotion from one person to another. Previous research has suggested that negative emotions, especially fear, can be conveyed to others through bodily odours, so-called chemosignals.
Chemosignalling is a recognised phenomenon in some animal species, such as rodents and deer. It is still a matter of debate whether chemosignalling occurs in humans.
The researchers aimed to see if positive emotions can also be transferred through chemosignals. In essence, whether smelling the sweat from someone in a happy state could induce happiness.
What did the research involve?
Sweat samples were taken from men during conditions designed to make them feel fearful, happy or neutral. Women were then asked to smell the samples and their emotional reaction was measured by their facial expression and reported emotion. Their level of attention was also tested, as researchers say that "happiness broadens the attentional scope" while fear narrows it.
Nine healthy Caucasian men of average age 22 provided sweat samples. The samples were collected using armpit pads during three separate sessions, each one week apart.
In the first session the researchers tried to induce fear in the men by showing them nine film clips.
The second session aimed to make the men feel happy, and included a clip of the "Bare Necessities" from the Jungle Book and the opera scene from The Intouchables (a "feelgood" film about the growing friendship between a disabled man and an ex-prisoner).
The final session involved neutral TV clips such as weather reports. The men washed their armpits before the sessions commenced and the pads were frozen after the sessions.
The men were asked to abstain from the following activities for two days before each session to avoid "contamination" of the sweat samples:
- drinking alcohol
- sexual activity
- eating garlic or onions
- excessive exercise
Whether the sessions induced the desired emotional effect in the men was assessed using a Chinese symbol task and a questionnaire. The Chinese symbol task involves looking at Chinese symbols and rating them on a scale from pleasant to unpleasant compared to the average Chinese character. The task is meant to give an indication of the state the viewer is in when they see the characters, rating them as more pleasant when in a happier mood. The questionnaire asked the men to rate how angry, fearful, happy, sad, disgusted, neutral, surprised, calm or amused they felt, each on a scale of one (not at all) to seven (very much). The men were paid 50 euros for participating.
The sweat pads were thawed, cut up and placed in vials to create happy, neutral or fearful samples. Each sample type was placed under the nose of 35 female students. Their facial expressions in the five seconds after smelling the vials was captured using electromyographic (EMG) pads. These devices are used to capture electrical activity produced by muscles and moving bones (e.g. whether they smiled or grimaced).
The students also completed the Chinese symbol task and other tests to measure their level of attention while smelling each vial.
After all vials had been smelled, the women were asked to rate them for how pleasant and how intense they found them. They were also asked to say whether they thought the samples came from happy, fearful or neutral individuals. They were paid 12 euros for participating.
All men and women recruited were heterosexual – to try and standardise chemosignals emitted by the men, and response from the women.
What were the basic results?
The combined test results for the men suggested that mainly positive feelings were induced by the happiness condition and negative feelings for the fear condition:
- the men reported feeling happier and more amused in the happy condition
- feelings of fear and disgust were higher in the fear condition
- the men had lower levels of arousal in the neutral condition
In the females, a happy facial muscle EMG response was more likely if the male sample was taken in a happy condition. If the sample was taken in the fear condition, the EMG was more likely to show a fear response in the women. The women performed better in the tests measuring wider attention ability when they smelled sweat provided in the happy condition. The sample condition had no effect on the Chinese symbol task or the reported odour intensity. Women could tell if the sweat had come from men in the happy or fearful condition compared to the neutral condition.
How did the researchers interpret the results?
The researchers concluded that: "exposure to sweat from happy senders elicited a happier facial expression than did sweat from fearful or neutral senders". They say: "humans appear to produce different chemosignals when experiencing fear (negative affect) than when experiencing happiness (positive affect)".
The findings from this small experimental study suggest that smelling sweat produced during different emotional states can influence people’s feelings.
However, the study has many limitations and cannot prove this theory. It only looked at sweat samples from nine men, and all of the testers were female students. The researchers say this was deliberate because men sweat more and women have a better sense of smell and greater sensitivity to emotional signals. Nevertheless, this means that we do not know if similar results would be found for men smelling female sweat or within the same sex. We also don’t know whether results would be similar if the women had been with the men at the time and smelling the sweat directly from their body, rather than in a vial that has been placed under their nose.
The study aimed to assess the feelings induced by the smell through facial muscle changes, reported mood and attention. It is not possible from such a study to be able to say with any certainty that any changes were due to the smell.
Other confounding factors could have caused the effects.
In real-life situations, where people are together and more than just smell is involved, emotional responses are due to a combination of thoughts, feelings, environmental factors and all of the senses.
While interesting, this study does not prove that body odours can transmit happy or sad feelings to others.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.