By Dr. Mercola
You catch a whiff of pumpkin pie, school glue, newspaper, or fresh-cut grass and suddenly you’re immersed in a flurry of vivid memories, often from your childhood. What is it about smells that can trigger memories so strong and real it feels like you’ve been transported back in time?
It’s known as “odor-evoked autobiographical memory” or the Proust phenomenon, after French writer Marcel Proust. In his famous novel In Search of Lost Time, the narrator dips a madeleine cookie into a cup of tea and is transported back into time as long-forgotten memories of his childhood come flooding back.
Indeed, research shows that odors are especially effective as reminders of past experience, much more so than cues from other senses, such as sights or sounds.1
One reason this might be has to do with the way your brain processes odors and memories. Smells get routed through your olfactory bulb, which the smell-analyzing region in your brain. It’s closely connected to your amygdala and hippocampus, brain regions that handle memory and emotion.
The close connection may explain why a scent might get tied to vivid memories in your brain, and then come flooding back when you’re exposed to that particular odor trigger. As noted by Psychology Today:2
“Interestingly, visual, auditory (sound), and tactile (touch) information do not pass through these brain areas. This may be why olfaction, more than any other sense, is so successful at triggering emotions and memories.”
Odor-Cued Memories Tend to Be Stronger, More Emotional, and from Earlier in Life
Before reaching your thalamus, smells first wind their way through other regions of your brain, including areas controlling memory and emotion. So with scents, you have all this extra processing even before you have conscious awareness of the scent.
Your body also contains far more receptors for smells (at least 1,000) than it does for other senses, like sight (four) and touch (at least four).3 What this means is you can discern between many different types of smells, even those you may not have the words to describe.
Taken together, this makes odor-cued memories particularly poignant and different than other memories. In one study of older adults, for instance, the participants were given three cue types (word, picture, or odor) and asked to recall memories triggered by the cue.4
It turned out the odor-cued memories tended to be older memories from the first decade of life, whereas those associated with verbal and visual information were from early adulthood.
The odor-evoked memories were also associated with “stronger feelings of being brought back in time” and had been “thought of less often” than memories evoked by the other cues.
Separate research also revealed that both young and old adults were able to recall more than twice as many memories when they were associated with an odor, which according to researchers provides “evidence for substantial olfactory cuing that is remarkably intact in old age.”5
Smells Can Trigger Traumatic Memories, Fears
It’s not only positive associations and memories that are brought back by different odors. For instance, odors are known to induce physiological arousal and trigger trauma-related flashbacks.
They’re also thought to play a role in triggering disturbing memories in people with post-traumatic stress disorder (PTSD).6
Intriguingly, a mother’s fears may even be passed on to her children via scent. In one study, female rats were conditioned to fear the smell of peppermint before they were pregnant. Later, the rats’ pups were exposed to the peppermint scent along with a scent of their mother’s reacting to the peppermint odor.
The newborn pups learned to fear the smell even when their mothers weren’t there, after just a single exposure.7 However, when activity was blocked in the pups’ amygdala, a region of the brain that processes emotions, including fear responses, the pups did not learn to fear the peppermint scent.
So it seems that, via scent, “infants can learn from their mothers about potential environmental threats before their sensory and motor development allows them a comprehensive exploration of the surrounding environment.”8
The impact of scent on fear was so strong that some of the rats tried to plug the tubing to stop the scent from coming in, a habit that the researchers plan to study further.
The Power of Scents Reveals Why Aromatherapy Is so Effective
Odor-evoked autobiographical memories typically occur by happenstance, when an unsolicited odor passes by your nose and you happen to catch a whiff. You can, however, harness the power of scents to trigger real physical and emotional responses through the use of aromatherapy. For instance, research shows:
- A systematic review of 16 randomized controlled trials examining the anxiolytic (anxiety-inhibiting) effects of aromatherapy among people with anxiety symptoms showed that most of the studies indicated positive effects to quell anxiety (and no adverse events were reported)9
- People exposed to bergamot essential oil aromatherapy prior to surgery had a greater reduction in pre-operative anxiety than those in control groups10
- Sweet orange oil has been found to have anxiety-inhibiting effects in humans, supporting its common use as a tranquilizer by aromatherapists11
- Ambient odors of orange and lavender reduced anxiety and improved mood in patients waiting for dental treatment12
- Compared to the controls, women who were exposed to orange odor in a dental office had a lower level of anxiety, a more positive mood, and a higher level of calmness. Researchers concluded, “exposure to ambient odor of orange has a relaxant effect”13
Anxiety, of course, is only one use for aromatherapy. Other potential uses are varied and include the following:
- Green apple scent for migraines: One study found that the scent significantly relieved migraine pain. This may also work with other scents that you enjoy so consulting with an aromatherapist might be beneficial
- Peppermint for memory: The aroma of peppermint has been shown to enhance memory and increase alertness
- Nausea and vomiting: A blend of peppermint, ginger, spearmint, and lavender essential oils has been found to help relieve post-operative nausea14
- Lavender for pain relief: Lavender aromatherapy has been shown to lessen pain following needle insertion15
Your Sense of Smell Is Even an Indicator of Your Health
If you still have a keen sense of smell, count yourself lucky, as olfaction (sense of smell) is strongly linked to many diverse physiological processes. Using data from a nationally representative sample of more than 3,000 older US adults, researchers form the University of Chicago found those with an inability to perceive odor (known as anosmia) were more than four times as likely to die in five years compared to those with a healthy sense of smell.16
Specifically, 39 percent of the participants who failed the first smell test (which consisted of identifying five common scents) died in the next five years, compared to 19 percent of those who had moderate smell loss and 10 percent of those with a healthy sense of smell.
A loss of the sense of smell was a remarkably strong indicator of approaching death, even more so than known leading causes of death, and independent of known risk factors like nutrition, cognitive function, mental health, smoking, alcohol abuse, or frailty. Loss of sense of smell was a stronger predictor of death than even a diagnosis of cancer, heart failure, or lung disease.17
Loss of olfactory function is probably not a cause of death, but rather may “serve as a bellwether for slowed cellular regeneration or as a marker of cumulative toxic environmental exposure,” the researchers said. As The Guardian reported:18
“The tip of the olfactory nerve, which contains the smell receptors, is the only part of the human nervous system that is continuously regenerated by stem cells.
The production of new smell cells declines with age, and this is associated with a gradual reduction in our ability to detect and discriminate odors. Loss of smell may indicate that the body is entering a state of disrepair, and is no longer capable of repairing itself. The olfactory nerve is also the only part of the nervous system that is exposed to the open air. As such, it offers poisons and pathogens a quick route into the brain, and so losing smell could be an early warning of something that will ultimately cause death.”
Could Your Sense of Smell Use a Boost?
If you’re missing out on old childhood memories because your sense of smell isn’t what it used to be, there are steps you can take to improve it. For starters, check for zinc deficiency. Zinc, an essential trace mineral, is required to produce an enzyme called carbonic anhydrase (CA) VI, critical to taste and smell, which is why loss of sense of smell is one of the classic signs of chronic zinc deficiency.
Mild zinc deficiency is relatively common, especially in infants and children, pregnant or breast-feeding women, elderly, people with poor gastrointestinal absorption or bowel disease like Crohn's disease, and for those eating vegetarian or vegan diets. Good source of dietary zinc include meats, oysters and wild-caught fish, raw milk, raw cheese, beans, and yogurt or kefir made from raw milk.
If you are healthy and you eat a well-balanced diet, you will rarely need supplements to complete your body's zinc needs, and you should strive to get zinc from dietary sources. If you know you’re not zinc deficient, I’d suggest reading through my nutrition plan for a comprehensive dietary plan that will support your health on multiple levels. Next, try these tips that are known to boost your sense of smell:19
- Exercise: Research shows that the more you exercise, the less likely you are to develop problems with smelling as you age. Exercising even one time a week was found to reduce the risk of losing your sense of smell20
- Become scent conscious: Make a point to smell your food before you eat it, and notice the scent of flowers, cut grass or even rain. Doing this regularly will help increase your sense of smell.
- Try “sniff therapy”: Choose three or four different scents, such as floral, fruity, and coffee. Sniff them four to six times a day, which will help the different receptors in your nose to work better