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You know those small vials of fragrant oils sometimes placed on a hotel pillow to calm a guest and improve sleep? Well, science says they work, even suggesting certain aromas can help build better brains—and memories—during sleep.

Researchers writing in a July 2023 issue of Frontiers in Neuroscience contend “olfactory enrichment”—inhaling pleasant fragrances during sleep—influences brain function in ways that significantly improve cognition and boost memory.

How Scientists Conducted the Study

Of 43 study participants—all healthy men and women between the ages of 60 and 85—20 underwent two hours of aromatherapy nightly. Seven different fragrant oils were dispersed through a room diffuser on a rotating basis—a different one each night—for a period of six months. When compared to the control group, the 20 volunteers registered a whopping 226 percent increase in cognitive capacity as measured by a word list test commonly used to evaluate memory.

The exact protocol is as follows:

• Participants provided an odorant diffuser made by Diffuser World
• Provided seven essential oils: rose, orange, eucalyptus, lemon, peppermint, rosemary, lavender
• Participants were asked to turn on the diffuser before bedtime—producing scent for two hours
• Rotate through different scents each night
• Continue nightly for six months

While this study was conducted in older adults aged 60-85, with no cognitive issues at all, there is some chance this may help younger groups as well. At a minimum, the side effects, or risks of sleeping with scented aromas, are quite minimal.

The finding supports past studies, including a 2021 report in the journal Geriatric Nursing indicating olfactory stimulation could prove a “simple and convenient new intervention for alleviating, maintaining [and managing] cognitive function and [behavior and psychological symptoms] in older adults with dementia.”

So, why is the sense of smell so critical to cognition, emotion, and general neural function?

Smell Directly Linked to Memory

Unlike the other senses, such as eyesight and hearing, the olfactory nerves are linked directly to a white matter pathway in the brain—the uncinate fasciculus—which plays a significant role in learning and memory encoding. It is part of the brain’s limbic system, which governs emotions and behavior.

It is this pathway that deteriorates due to aging and the development of neurodegenerative disorders like Alzheimer’s and Parkinson’s disease, authors of the July 2023 journal article state. In fact, the sense of smell is much like the canary in the cave, where the bird’s sensitivity to adverse conditions and resulting death, is a warning to miners to get out quickly. Loss of smell can prove a warning of the onset of some 70 different neurological disorders or neural infections. Traumatic brain injuries can also modify or interfere with olfactory discrimination.

The researchers were quick to point out that olfactory stimulation does not directly affect areas of the brain responsible for controlling sleep. However, they say the use of natural fragrances can deepen slow-wave sleep. Slow-wave sleep is considered “the most restful portion of the sleep cycles,” study authors write. “Odorants enhance normal sleep, and…also improve abnormal sleep at a magnitude similar to that of sleep medications.”

Meanwhile, the National Sleep Foundation says that smell can affect “how long it takes to fall asleep, [as well as] overall sleep quality and quantity. Distinct scents may promote better sleep, help people wake up in the morning, or even [potentially] influence dreams and memory formation during sleep.”

Key components of what is defined as “quality sleep” include duration, continuity (number of times one awakens during the night), and amount of beneficial slow wave (deep) sleep, which is important in enhancing memory, strengthening the immune system, repairing bone and tissue, and regenerating cells.

Lavender Most Studied, But Other Oils Also Beneficial

The most studied fragrance for improving sleep has been lavender, but past reports also cite the appealing effects of natural oils like jasmine, rose, and Roman chamomile, which reportedly is effective in easing anxiety and depression, and even cedarwood. All of these are extracts derived from plants.

In a 2021 article published in Complementary Therapies in Medicine, authors review 30 aromatherapy studies and conclude the use of fragrant oils has a “statistically significant” effect on improving sleep quality and reducing “stress, pain, anxiety, depression, and fatigue.” Indeed, aromatherapy also appears effective for controlling cases of acute insomnia, they state. And now, of course, the latest study indicates the smell of these oils can make the user smarter in terms of cognition, recall, and judgment.

The therapeutic effects of natural fragrances are not a new concept. Pedanius Discorides, a Greek physician considered the father of pharmacognosy, discussed the medicinal properties of natural plant oils in his book De Materia Medica, written in the first century. Later, in the 12th century, Saint Hildegard, a German Benedictine abbess, composer, philosopher, and medical writer, used distilled lavender for healing purposes.

Finding the Best Way to Use Fragrances

Having a scientifically approved approach to enhancing sleep quality, while building cognition and memory, through the use of natural fragrances could benefit tens of thousands of Americans. Impaired sleep is reaching epidemic proportions in the United States. The National Sleep Foundation estimates more than a third of adults fail to sleep the required number of hours. The Centers for Disease Control and Prevention says the number is closer to 35 percent.

Chronic insomnia and other forms of sleep deprivation are linked to a variety of physical, mental, and psychological symptoms. These include mood shifts and increased irritability, concentration and attention problems, failures in judgment and executive decision-making, physiological changes, such as impairments in brain function and hormone production, reduced immunity protection from disease, overstimulated appetite and weight gain, higher risk for diabetes and various dementias, an overactive nervous system, chronic fatigue—even earlier death. This list includes a range of psychiatric disorders, including elevated anxiety, depression, and obsessive compulsiveness.

As the author Rachel Carson once wrote,

For the sense of smell, almost more than any other, has the power to recall memories.

Indeed, 21st-century science is proving her right.