For some time now, studies have been abound on the benefits of nature for both physical and mental health. Now, however, research shows that smells derived from nature may be able to lower physiological stress levels better than visual and auditory stimuli.
As most research looking at the benefits of nature on health outcomes have come from self-evaluations, researchers from Sweden decided to take a more quantifiable approach to prove any link between nature and stress reduction.
Based on findings from previous research, they hypothesized that environments rich in biodiversity would be able to reduce stress levels faster than non-natural environments. To test their theory, they subjected 154 participants to one of three environments generated by virtual reality: a city, a park or a forest. Throughout the experiment, the participants not only experienced these environments via virtual reality headsets; they also wore earphones hearing the scenescapes’ sounds, and had the appropriate smells pumped directly into their nostrils.
Asked to rate how pleasant they found each stimuli on a scale of 1 to 100, the researchers also administered a small electric shock to each participant to stimulate a moderate physiological stress response measurable as a slight increase in electrical conductance in each participant's skin. The researchers then tracked how quickly each participant's skin conductance levels rose and fell in each environment to identify which was best to reduce stress levels.
In the end, the researchers found that on average, skin conductance rose the highest for those in a cityscape. Meanwhile, skin conductance fell fastest for those in forest and park scenes- with little discrepancy between the two. The researchers also found that the rated pleasantness of smells was the strongest predictor of stress levels- with high pleasantness being linked with lower stress responses and faster recovery. Taken together, these findings suggest that smells may have a larger stake in our stress response and recovery than audio and visual stimuli. But why?
Unlike other senses, smells are not first processed by the thalamus (the brain’s switchboard). Instead, they pass directly to the hypothalamus, the brain’s centre for responding to stress, as well as the olfactory cortex, where they are then processed and perceived. By bypassing the thalamus in this way, smells are able to be processed by other parts of the brain faster, leading to a faster response from the brain than other sensory inputs.