A particular scent can bring back memories of someone important or a happy place. If that pleasant feeling continued while we slept, could it brighten the emotions in our dreams too?
In 2024, Lenka Martinec Nováková and colleagues conducted an experiment with 20 healthy young adults, dispersing a pleasant, self-selected scent in their bedrooms. They examined whether dreams became more pleasant, whether emotions within dreams changed, and whether mood improved immediately after awakening.
A Personally Meaningful Scent Rather Than a “Generally Pleasant” One
The study emphasized individual scent preferences. Rather than giving everyone the same scent, the researchers asked participants to choose one associated with positive memories or pleasant imagery.
They provided 40 commercially available room fragrances. During the first visit, participants smelled them one by one and selected a scent that evoked strong positive memories or emotions. If none did so, they were asked to choose a pleasant scent they would consider using in their own bedroom.
In practice, eight participants chose on the basis of pleasant imagery rather than a specific emotional memory. This was therefore not a study in which everyone brought in “the very scent of a special memory.” Even so, the selected scents were rated as pleasant and somewhat familiar on average.
Three Overnight Visits to Compare Scented and Unscented Nights
The participants’ mean age was approximately 25 years. They spent three nights in the sleep laboratory, one week apart. The first night was for adapting to the setting and procedures and was not included in the main comparison. On the remaining two visits, they experienced a scented and an unscented night in randomly assigned order.
On the scented night, a home diffuser containing the selected cartridge ran continuously from 10 p.m. until the following morning. On the comparison night, the same device was run without a cartridge. This setup was designed to resemble sleeping in a scented room at home more closely than a method that delivers brief pulses of odor to the nose.
Brain waves, eye movements, and other signals were recorded during sleep. After 2:30 a.m., the researchers identified REM sleep and woke the participant once it had continued for five minutes. The main comparison concerned the dream experience reported at this nighttime awakening and mood immediately afterward. It did not investigate whether participants “felt good throughout the following day.”
If participants remembered a dream, they rated its pleasantness, emotional intensity, positive emotions such as joy and affection, and negative emotions such as fear and sadness. Separately from dream emotions, they were also asked whether their own mood at that moment was pleasant or unpleasant.
Neither Dreams Nor Mood Immediately After Awakening Clearly Improved
Comparing scented and unscented nights revealed no statistically clear differences in dream pleasantness, emotional intensity, positive or negative emotions, or mood immediately after awakening. Effect sizes, which describe the magnitude of differences, were also small. The authors concluded that the practical value of improving dreams or mood under these conditions was very limited.
However, dreams from all 20 participants could not be compared across both nights. Fifteen participants recalled dreams in each condition. Paired data from both conditions were available for 12 participants for each dream measure and 14 for mood immediately after awakening. Technical problems with the recording equipment also contributed to the failure to obtain the planned 20 paired datasets for analysis.
Because this was a small comparison, the failure to find a difference cannot simply be taken as “proof that the effect is exactly zero.” At the same time, the lack of the expected improvement even when participants selected a preferred scent is an important result when considering this use of fragrance.
Why Did a Preferred Scent Not Change the Dreams?
One possible explanation is that continuous, prolonged exposure led participants to become accustomed to the odor. However, this was not confirmed as the cause of the result. Twelve participants reported noticing some odor in the room on the scented night, but that question alone could not distinguish whether they had noticed their selected scent or another odor already present in the room.
The selection method also has limitations. Choosing one of 40 scents is not the same as freely bringing a fragrance that a participant regularly uses and enjoys. Questions remain about the burden of comparing many scents in an unfamiliar laboratory and whether the choice made that day adequately represented the person’s preference.
To approximate conditions at home, the researchers did not take steps to conceal the presence or absence of scent while participants were awake. The possibility that expectations about scent influence how dreams are recalled also needs future consideration. Exploratory findings showed differences in some emotion ratings depending on whether scent was presented on the second or third visit, but these were not the main results establishing a scent effect.
Summary
Sleeping in a room scented with a personally preferred fragrance did not clearly improve dream emotions or mood immediately after awakening from REM sleep in this small experiment. The authors consider the practical value of using scent to improve dreams under these conditions limited in healthy young adults.
This conclusion does not rule out enjoying fragrance while awake or using other presentation methods. When considering how scent might act, its meaning to the individual and when and how it is delivered need to be considered alongside its name. While preserving the importance of these factors, the study shows that claims of improved dreams require careful assessment.
References
Martinec Nováková, L., Miletínová, E., Kliková, M., & Bušková, J. (2024). Nocturnal exposure to a preferred ambient scent does not affect dream emotionality or post-sleep core affect valence in young adults. Scientific Reports, 14, 10369. DOI: 10.1038/s41598-024-60226-z / Full original article.
Original article license: CC BY 4.0. © The Author(s) 2024.
