Light a candle steeped in lavender oil and you will – supposedly – start to feel relaxed. The smell of ginger oil, some say, will aid digestion, and clove oil will help arthritis. Aromatherapy is often touted as a form of complementary medicine, but do its supposed health benefits have any scientific merit?
Two recent studies presented at the American Physiological Society’s annual Experimental Biology conference have shown that for horses and mice, at least, aromatherapy can help alleviate stress and anxiety.
One study, led by George Washington University neuroscientist Cassandra Moshfegh, showed how mice exposed to orange essential oil were quick to improve on stress and anxiety markers. The researchers suggest essential oils might one day be used to help relieve post traumatic stress disorder (PTSD).
In the second study, Albion College student Kylie Heitman observed that a lavender diffusion calmed competition horses in the small confines of a horse trailer.
“Olfaction is a very primitive sense, it’s the oldest of the five senses,” says Australian National University neuroscientist John Bekkers, who was not involved in either study. “As a consequence, there are a lot of connections between the smell and emotional parts of the brain.”
In Heitman’s test, the horses who breathed in the lavender scented air had lower levels of cortisol – a hormone the body releases under stress – compared to the control horses.
And Moshfegh used Pavlovian fear conditioning to test the effects of orange essential oil. The mice were conditioned to associate fear with a particular sound, and would then freeze in fear when they heard it again. Over time, after hearing the sound repeatedly, the mice become less afraid.
The researchers found the terrified mice who sniffed the orange aroma recovered from their fear faster than the mice who didn’t.
But is there anything inherently calming about the scent of lavender or orange?
Generally, the brain puts smells into one of two categories: smells that are “hard-wired” into our evolution – for instance, pheromones for mating purposes – and smells that are learned.
In other words, most of the time we think a smell is pleasant because we’ve learned pleasant associations with it.
“I’m having a hard time understanding how a mouse would associate the smell of orange with something nice, or even a horse with lavender,” Bekkers says.
But the results of both studies were preliminary, he adds, and speculates that lavender, for instance, might have a slight anaesthetic effect.
In the case of Moshfegh’s study, Bekkers cautions that the connection between aromatherapy and PTSD has not been confirmed.