Q: I understand that various fragrances have an effect on our thinking and behavior. But how?
A: There are two main theories: a physiological theory and a psychological one.
A researcher at Warren Alpert Medical School in Brown University wrote an article called “Aromatherapy Facts and Fictions” to discuss the research regarding mood, physiology, and behavior. It was published in the International Journal of Neuroscience in 2009.
Here are some key things that the author noted in her article.
FIRST, there’s an important thing to note about terminology.
- Aromatherapy is a sort of “folk science” regarding how scents can be used to heal. In science, aromatherapy is not yet considered scientifically supported. Lots of junk science here.
- Aromachology is the scientific study of olfactory effects in humans. If you want to talk about the science of smell, you should use the term “aromachology” to really show that you’re talking about science.
How do aromas have an effect on us? There are two theories that explain how fragrances affect our behavior.
The Pharmacological Hypothesis
- According to this hypothesis, fragrances affect our systems directly, including:
Endocrine system (hormones)
In this way, fragrances act on our bodies like drugs. They enter into our bodies and mess with various hormone levels and neurotransmitters in order to produce change.
If this hypothesis is true, it means that fragrance chemicals must somehow get into our bloodstream. Possibly, these chemicals could enter the body through the:
- Nasal mucosa (mucus membranes in the nose)
- Lung mucosa (mucus membranes in the lungs)
- Olfactory nerves (skipping the bloodstream and getting directly into the brain through the nerves in our nose)
- Some fragrances, like lavender, have been shown to directly influence certain chemicals in the brain.
- Studies with rats have shown that if the olfactory system is destroyed, some fragrances still have effects. This suggests that it’s not the “smell” but the chemicals being absorbed into the body.
There isn’t any data yet on fragrances getting into the bloodstream of humans.
The odor levels of “aromatherapy” or inhalation of oils, etc. don’t really contain enough chemicals to really affect the body that much (this might be why effects are seen in rats but not so much in people – rats are much smaller and have much greater senses of smell).
You’d have to inject large amounts of those chemicals directly in the body to really see them influence a person physiologically.
The effects of fragrances happen extremely quickly. If you drink a caffeinated beverage, for instance, it could take 20 minutes for the chemical to enter into your body and really influence your behavior.
20 minutes is the average time it takes for bloodstream chemicals to influence a person.
Fragrances can affect you almost immediately. That’s not enough time for a chemical to really be metabolized or influence your body.
Finally, here’s something clever: scientists have tested molecules of scents that are chemically very similar but the scents are extremely different.
- For instance, there’s a chemical called carvone. There are two slightly different variations of carvone that smell extremely different – one smells like caraway (a spice) and one smells like spearmint.
- The two chemicals should effect the body similarly because they’re so chemically similar.
- However, they have very different effects on the body (one has very little effect on physiology, and one causes increases in pule rate, blood pressure, and restlessness).
- Therefore it has to be the scent, not the molecule, which makes the difference.
- This type of experiment has been done with several chemicals, such as limonene and linalool.
The Psychological Hypothesis
- On this theory, fragrances produce effects through our experience and learning, memories, conscious perception, beliefs, and expectations.
So, for instance, the smell of dogs can be quite different for those who had a beloved childhood dog, and those who have been attacked by a dog.
- Fragrances are highly tied to emotional memories – good and bad.
There are direct connections between the effects of smell and the parts of the brain associated with emotions and memories.
The olfactory nerve (smell) travels right next to the amygdala and the hippocampus, both involved with strong emotions and memories and learning.
Whether you like a smell tends to be directly related to how it affects your mood. If a fragrance has been shown in a lab to have a certain effect, but you don’t like the smell, that effect doesn’t tend to work with you!
According to the research, the strongest factors that influence the effect fragrances have on you are:
- Hedonic characteristics (in other words, whether the smell is simply pleasant to you)
- Culture (various cultures have different meanings attached to fragrances)
- Personality (certain personality traits increase a person’s sensitivity to smells)
Think of it this way – fragrances probably affect a person the same way that music affects a person. It doesn’t change your hormone levels directly. Instead, it influences your brain systems involved with perception and memory.
- Sometimes you’re in the “mood” for a fast and loud song, sometimes a quiet song.
- Sometimes a song reminds you of a good memory of a person.
- Sometimes a song really speaks to your personality or culture.
- Fragrances work the same way!
A study was done in 1966 to see what fragrances people liked. Both British and American participants were surveyed.
For the British, wintergreen was given one of the lowest pleasantness ratings. For the Americans, wintergreen was one of the highest. Why?
Because in Britain, between WWII and the ‘60s, wintergreen was a scent used for medicines and analgesics. In the United States, wintergreen wasn’t used for medicines, it was used for popular candies.
So for the British, wintergreen just reminded them of injuries, doctors, and hospitals!
Whether the participants liked wintergreen was based on their memories and associations.
Between the two hypotheses, it seems that the psychological hypothesis is correct. Fragrances don’t really enter the bloodstream and they aren’t strong enough to make a difference even if they did. They don’t seem to influence body chemicals directly.
Instead, our senses of smell are far more fluid and psychological than that. Fragrances interact with our beliefs, personal histories, memories, and expectations.
This means that we should expect fragrances to affect people differently, based on their cultures, histories, expectations, etc.
Unfortunately it doesn’t seem like there are “universal” responses to scents.
But it explains why people have different tastes when it comes to fragrances.
It also explains why we can change a person’s beliefs or expectations about a smell and that influences whether they like the smell.
Herz, R. S. (2009). Aromatherapy facts and fictions: A scientific analysis of olfactory effects on mood, physiology, and behavior. International Journal of Neuroscience, 119, 263-290. Link: https://www.ncbi.nlm.nih.gov/pubmed/19125379