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Scientists have found that scent exposure may help improve memory in some older adults. elenaleonova/Getty Images
  • Being regularly exposed to multiple scents—or olfactory enrichment—has shown promise in enhancing cognitive abilities in older adults.
  • However, not all studies have yielded consistent results.
  • A new study found that using aromatherapy essential oils such as lavender and rose nightly boosted word recall by 226% and improved the functioning of a key brain pathway that plays a role in learning and memory.
  • These findings suggest that olfactory enrichment may be a low cost approach to reduce neurological impairment in older adults.

In the United States, cognitive decline, which is characterized by confusion or memory loss, is estimated to affect 11.1% of the population, or one in nine adults.

Previous research has shown that cognitive decline is accompanied or even preceded by loss of sense of smell in various neurological disorders, including Alzheimer’s disease, dementia, and Parkinson’s disease.

Some research indicates that regular exposure to multiple scents or odorants — a practice known as olfactory enrichment — can have beneficial effects on cognitive abilities in older adults.

In a new clinical study, researchers at the University of California, Irvine, examined if a nightly aromatherapy regimen for six months could improve cognitive skills in older adults.

They observed significant improvements in word list recall as well as improved functioning in the part of the brain known as the left uncinate fasciculus after olfactory enrichment with aromatherapy oils.

The study received funding from Procter & Gamble.

The findings were published in Frontiers in Neuroscience.

For the study, the researchers recruited 43 participants, ages 60–85 years, who were in good general health with healthy cognition.

The participants were randomly assigned to two groups. The experimental group, made up of 20 individuals, was exposed to essential oils nightly. Meanwhile, the control group, made up of 23 participants, was exposed to trace amounts.

For six months, the participants were exposed to either a higher or lower concentration of essential oils nightly for two hours as they were going to sleep, using a nebulizing fragrance diffuser.

The diffuser rotated through seven different scents from The Essential Oil Company (Portland, Oregon), one for each day of the week: rose, orange, eucalyptus, lemon, peppermint, rosemary, and lavender.

All participants underwent a set of assessments at study entry (baseline) and after the 6-month intervention:

  • cognitive assessments, including a pattern separation test that assesses a person’s ability to distinguish between 2 similar stimuli
  • questionnaires on depression and quality of life
  • tests of olfactory performance
  • functional magnetic resonance imaging (fMRI) to check for changes in brain structures and brain structural connectivity.

They found that, compared to the control group, participants in the olfactory-enrichment group displayed a 226% improvement in their performance on the Rey Auditory Verbal Learning Test—a word list recall test used to assess verbal learning and memory.

Additionally, they observed improved functioning in the left uncinate fasciculus, as assessed by mean diffusivity — the average water diffusion rate within brain tissue.

The uncinate fasciculus is a brain pathway that plays a crucial role in learning and memory and deteriorates with age and Alzheimer’s disease.

The researchers concluded that minimal olfactory enrichment using an odorant diffuser at night significantly improves verbal memory and the integrity of a specific brain pathway.

“It therefore may be appropriate to begin envisioning olfactory enrichment as a low cost public health program to reduce neurological risk in older adults,” the authors write in the study paper.

For example, in a 2018 study, adults who experienced olfactory enrichment with four essential-oil odorants twice a day for five months had significantly improved olfactory function and verbal function, and decreased depression symptoms compared to controls who solved daily Sudoku puzzles instead.

Not all olfactory enrichment studies have produced the desired results, however. A 2022 study did not find memory improvement in older adults with mild cognitive impairment after brief exposures to multiple odorants twice each day for four months.

Dr. Michael Leon, professor emeritus of neurobiology and behavior at the University of California Irvine, and senior author on this study, explained to Medical News Today that “[i]t was known that the loss of olfactory stimulation causes the memory centers of the brain to deteriorate and it turns out that increasing odor stimulation improves the memory centers of the brain along with memory.”

“The olfactory sense is the only sense that has direct access to the memory centers of the brain and [aromatherapy] is a good way to stimulate those centers with little effort,” he added.

Dr. Mark Moss, head of the Department of Psychology at Northumbria University in the United Kingdom, who was not involved in the study, meanwhile, noted that “in the context of the current study, the rotation of aromas on a nightly basis provides environmental enrichment.“

“Olfactory enrichment has been shown to impact on human brain structure and to impact on aspects of memory when presented during daytime studies.”
— Dr. Michael Leon

Dr. Moss said the study had a number of strengths.

“First, the intervention went on for six months, so this gives a good assessment of the long-term use of the aromas. The use of brain imaging can help in demonstrating how any behavioral effects might be mediated at the level of brain structure and function,“ he told MNT.

“A range of cognitive tests were employed to assess different cognitive functions; memory, working memory, attention switching, and planning. The use of a range of essential oils that were rotated on a daily basis over a week is a good element to the study to ensure environmental enrichment,” he continued.

However, the reliability of the findings is limited by the small number of participants who contributed data for the cognitive analyses. Due to the COVID-19 pandemic, many participants were unable or unwilling to return to the university campus for cognitive assessments at the end of the 6-month intervention.

This reduced the cognitive assessment dataset to a total of 23, 12 of whom experienced olfactory enrichment and 11 who were in the control group.

Dr. Aimee Spector, professor of old age clinical psychology at University College London in the U.K., who was not involved in the study, also commented that the sample size was very small and “a fully powered trial is needed to make any firm conclusions.”

The fact that none of the participants had cognitive impairment also meant that “there is a limit to the likely changes in cognitive function,” she told MNT.

“There is also likely to have been a placebo effect in that the control group were given distilled water and would therefore have known that they were not receiving treatment,” Dr. Spector pointed out.

Dr. Moss noted that “of the 12 cognitive measures they analyzed, only one produced a significant difference, so although a large effect was found for that particular variable, the potential median response over a 226% improvement may well be overblown. It is not exactly clear what the baseline scores were as only the change from baseline values are given.”

Overall, Dr. Moss believes that the “use of aromatherapy for a couple of hours a night is something worth trying” as it “can help with sleep quality as well as potentially on memory.”

However, he cautioned people not to expect “a definite improvement,” as “even amongst participants who received the aroma intervention in the study, only half improved their memory after six months.”