Source: French to English Tester Published on: 2026-05-11
Source: The Conversation – in French– By Coline Zigrand, PhD candidate in neuropsychology, Université du Québec à Montréal (UQAM)
Can a simple scent diffused during sleep improve your sense of smell, your memory, or even the quality of your sleep? New research explores the benefits of passive olfactory stimulation.
One person out of five has aloss or decrease of the sense of smell. This can occur as a result of various conditions, including a respiratory infection, sinusitis, a Covid-19 type infection, a head injury, aneurodegenerative disease or exposure to chemicals.
Invisible, it greatly reduces thequality of life.
Affected individuals may isolate themselves out of fear of smelling bad, experience anxiety, lose their appetite, or change their diet. Daily safety is also compromised, as detecting smoke, gas, or spoiled food becomes more difficult. Finally, this loss can harm certain professions, such as chef, perfumer, or sommelier, for whom the sense of smell is a vital work tool.
The main treatment for olfactory loss consists of a“olfactory training”. Every day, morning and evening, the protocol consists of exposing oneself to different odors for about 30 to 40 seconds per odor.
The limits of olfactory stimulation
Although the beneficial effects of olfactory stimulation are documented byseveral studies, the dropout rate ishigh. Indeed, to be effective, olfactory training requires two sessions per day for at least three months. This repetitive routine is demanding, and some give up before seeing the benefits.
To fill this gap, someresearchers have proposed a simple solutionand accessible: thepassive olfactory stimulation. It involves exposing the brain to various smells continuously, even during sleep.
A remodeling of the brain
Effortlessly and without medication, this nighttime practice is increasingly intriguing neuroscientists because of its benefits. Indeed, some studies show an improvement inmemory, a better quality ofsleepand even anatomical changes incerebral level.
These effects rely on brain plasticity, that is to say the brain’s ability to reshape itself based on experiences and learning. By smelling odors, we activate and stimulate the limbic system of the brain, a key region that regulates emotions and memory. Despite a rapidly expanding field of research, this approach remains little known to the general public. Its beneficial effects on the brain could improve the quality of life for many people, especially since complaints ofmemory, ofsleep or smellincrease with age.
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A “memory booster”
The smell of a sugar pie coming out of the oven can be enough to revive a childhood memory at grandmother’s. A true madeleine de Proust, this phenomenon illustrates the intimate link between smell and memory.
A study published inFrontier in Neuroscienceexposed a group of healthy adults aged 60 to 85 years to a different odor each night, that is seven odors in rotation over a week, for six months. Their results show a 226% improvement in their verbal memory compared to a group of non-exposed adults.
At the brain level, researchers reported an increase in the left uncinate fasciculus, a sort of communication highway between the brain regions involved in memory and learning. The fact that this structure is positively modified by passive olfactory stimulation suggests that the effects would not be merely ephemeral.
Thus, olfactory stimulation could act as a true “booster” for the memory of elderly people. However, although encouraging, these results need to be confirmed by other studies, notably due to the small sample size.
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Benefits for sleep
Smells and sleep are intimately linked, and have been for millennia. Already in ancient Egypt, our ancestors burned myrrh incense toprotect sleepers from nightmares. Today, research suggests that olfactory stimulation practiced at the time of falling asleep and during the night could effectively improve sleep.
Sleep is crucial for the proper functioning of our physical and mental health. Broadly speaking, sleep allows our body to recover, regulate emotions, and eliminate metabolic waste accumulated during the day, as well as support the immune system. It is also a key moment for consolidating memories, by transforming newly learned information into long-term memories. However, as we age,our sleep becomes more fragmented, contains more awakenings and we generally report lower quality sleep.
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Onemeta-analysisgrouping several studies demonstrates that certain scents can improve the sleep quality of people with insomnia. Lavender, orange peel, and rose are the most studied scents, although their respective therapeutic effects are still not well known.
In the same vein, apilot studyhas shown that the nocturnal diffusion of the scent of lavender can improve both perceived sleep and certain objective measures of sleep recorded by EEG. Compared to a night without scent, the night with the scent of lavender was associated with better well-being upon waking, a reduction in sleep disturbances, as well as an increase in deep slow-wave sleep (N3) and delta activity, a marker of deeper and restorative sleep.
These results remain preliminary, but suggest that passive olfactory stimulation during the night could promote better quality sleep.
Where to start?
No need for sophisticated equipment to get started with passive olfactory stimulation. Here are some ideas:
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Smelling a perfume, essential oils every morning or evening on clothes.
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Use a diffuser or a room fragrance in your living space.
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Exposing oneself to different odors.
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Smell at least 4 different odors. Each type for about 30 seconds in each nostril, twice a day for 3 to 6 months.
To prepare our body to fall asleep, we dim the light, seek silence, and put on loose clothing. We engage almost all our senses without even realizing it. So, why not add a soothing scent before closing our eyes?
Coline Zigrand received funding from the Fonds de recherche du Québec en santé (FRQS).
Benoît Jobin receives funding from the Canadian Institutes of Health Research (CIHR).
–ref. Can stimulating the sense of smell be beneficial for the brain?https://theconversation.com/can-stimulating-the-sense-of-smell-be-beneficial-for-the-brain-278265