Close your eyes and conjure up the following smells: a burst of citrus while peeling a juicy orange; the green piney scent of a fresh-cut Christmas tree; or a warm waft of perfume from a blooming lilac bush.
For millennia, ancient cultures like China, India and Egypt recognized that certain natural aromas are deeply soothing, and folk healers have long prescribed scented essential oils for treating stress-induced conditions like anxiety, insomnia and headaches. But science is still trying to figure out exactly how and why these potent aromas produce calming physiological responses.
Our sense of smell is triggered when fragrance molecules attach to special cilia-covered olfactory receptors in the nasal cavity. Those receptors then send electrical signals directly to the olfactory cortex of the brain, which in turn talks to the memory and emotion centers of the brain like the hippocampus, amygdala and frontal cortex.
A study out of Japan strengthens the theory that some smells can act like nature's own anti-anxiety medication, tweaking our brain chemistry in ways that mimic the effects of prescription drugs like Valium and diazepam. (The study was published on Oct. 23, 2018, in the journal Frontiers in Behavioral Neuroscience.)
In a series of experiments, Japanese researchers ran mice through mazes and other rodent stress tests while exposing them to an aroma called linalool, the organic compound that gives lavender its sweet floral scent. From previous studies, they suspected the linalool would lower anxiety levels in the mice, which it did. But the scientists also wanted to test a hypothesis that lavender's calming effect went straight from the mouse's nose to its neurons.
So they included mice in the study that were "asnomic," meaning they had no sense of smell. Those mice showed no effect of exposure to linalool, proving that the olfactory system was definitely the delivery mechanism. Next, they wanted to figure out if linalool was targeting the same receptors in the brain as some of the most common prescription anti-anxiety meds.
Drugs like Valium, Xanax, Klonopin and diazepam are all members of the same drug family called benzodiazepines. One of the causes of clinical anxiety is overactive neuronal activity in the brain. Benzodiazepines can inhibit or calm down neuronal activity by binding to particular sites on neurons called GABA receptors. When a drug like Valium binds to a GABA receptor, it increases the flow of certain chemicals into the neuron that mellow the brain out.
The Japanese researchers made a strong case that the smell of lavender acts on those very same GABA receptors. They did this by treating some mice with flumazenil, a drug that blocks GABA receptors. And when those treated mice sniffed the linalool, they didn't exhibit any calming effects.
As Powerful As Sleeping Pills
Lavender isn't the only aroma that's been linked to the same neuron receptors as potent anti-anxiety drugs. A few years ago, German researchers tested hundreds of fragrances on GABA receptors in rodents and humans and the big winner was jasmine, which delivered a GABA effect as powerful as sleeping pills and sedatives.
Lavender and jasmine are the first ancient relaxation remedies to be tested like this, but several others may share a similar nose-to-brain mechanism. According to the Japanese study, other compounds that have shown promising anti-anxiety effects in mice and men include limonene, the aroma of citrus peels, and pinene, the smell of pine trees.
Aromas aren't universally relaxing, though. Since smells share such a close neurological connection to memories and emotions, their physiological effects can also be altered by our personal experiences. Like Pavlov's dog, our brains can be conditioned to love or hate certain smells depending on our associations with them. For example, if your mom made you scrub toilets as a kid with a lemon-scented cleaner, you might not find the odor all that soothing.
Research has shown that the olfactory system has the strongest direct line to the hippocampus and the amygdala, which are the memory and emotional centers of the brain. This is why scent memories can evoke such powerful feelings of nostalgia. A smell can carry us back to a specific time and place in ways that conscious thinking and remembering cannot.
That might explain why we find the smell of baby powder so soothing; it summons feelings of security and love from deep in our earliest memories. But even that smell appears to have cultural variations. Americans associate the "new baby smell" with vanilla and "powdery" scents, while French babies smell like orange blossoms.