Does the smell of blood whet the appetite?
A team of student researchers from the Faculty of Psychological Sciences at the University of Melbourne, Australia decided to investigate how bloodthirsty humans really are.
Their experiment involved 64 unsuspecting volunteers who visited Science Gallery Melbourne’s exhibition Blood – Attract and Repel.
The intention of the research was to test two opposing hypotheses: 'anyone is repulsed by the smell of blood' or 'people appreciate the smell of blood as appetising'.
Participants were provided with images of cooked food and either an aroma of blood or a glass of water as an appetiser.
Due to the size of the experiment, the results remain suggestive. Though the findings did reveal that participants found images of cooked food more appealing after smelling the aroma of blood, than those participants who were provided with a glass of water as appetiser.
The association of appetite with the smell of blood was stronger in relation to meat dishes, but even vegetables were deemed more appetising when the smell of blood was in the air.
"The appetising effect of blood is really intriguing and definitely worth studying," says Will Turner, who led the research team of 11 students.
Scientists translated facial expressions of participants using facial recognition software built by Microsoft. Different responses such as negative, positive, sad, angry or afraid were recorded when participants were faced with the different scenarios and images of food.
Turner continued: "It was mainly a training exercise for us and an opportunity to help engage people in the working world of science. I didn't really expect to get any specific results to be honest, given the small numbers we shuffled around. While the results may only reveal a few interesting trends, they suggest that something is going on - and the potential is there to investigate this further with a more comprehensive study."
A 2015 study by researchers at the University of Konstanz, Germany, explored similar questions around odour by asking 89 students to evaluate their own emotional responses to several different smells exposed on their skin, including an artificial aroma of blood. The results from this previous experiment suggest that we have a complex, and perhaps misleading relationship with blood.
There is a range of theories as to why blood may be attractive or repellent. The University of Konstanz study suggests that the attraction to blood may reflect the evolutionary importance of being good at hunting and fighting, or perhaps it may be attractive because it signals prey, i.e. food.
Blood can also demonstrate a clear sign of danger. Some people have such an adverse reaction to blood that it can cause them to faint. The research also pointed out that the fear response to blood could be a reaction to its stress hormones contained within it, as opposed to its smell.
Decision psychology researcher Stefan Bode concluded: "If follow-up research shows that the smell of blood does indeed increase our appetite, it would suggest that this is a ‘basic instinct’ reaction as opposed to a learned one. It's not like the smell of coffee that can grow in appeal over a period of time and as a result, increase consumption."
References:
James K. Moran et al. The Scent of Blood: A Driver of Human Behaviour?, PLOS ONE (2015). DOI: 10.1371/journal.pone.0137777
Sara Nilsson et al. Behavioural Responses to Mammalian Blood Odor and a Blood Odour Component in Four Species of Large Carnivores, PLOS ONE (2014). DOI: 10.1371/journal.pone.0112694
Bowen J. Fung et al. High monetary reward rates and caloric rewards decrease temporal persistence, Proceedings of the Royal Society B: Biological Sciences (2017). DOI: 10.1098/rspb.2016.2759
