Researchers have demonstrated that some smells, such as those from rose-scented incense sticks, may facilitate better learning during sleep, a finding that could lead to better ways of improving memory retention.

In the study, published in the journal Scientific Reports, students in two school classes in Germany learned English vocabulary — with and without scent sticks during the learning period, and also at night.

The findings revealed that pupils remembered the vocabulary much better with a scent. “We showed that the supportive effect of fragrances works very reliably in everyday life and can be used in a targeted way,” said study co-author Jurgen Kornmeier from the University of Freiburg in Germany.

The scientists conducted several experiments with 54 students from two sixth grade classes of a school in southern Germany, who were asked to place rose-scented incense sticks on their desks at home while learning English vocabulary, and on the bedside table next to the bed at night.

In another experiment, the participants also placed the incense sticks on the table next to them during a vocabulary test at school during an English test.

The results were compared with test results in which no incense sticks were used during one or more phases.

“The students showed a significant increase in learning success by about 30 percent if the incense sticks were used during both the learning and sleeping phases,” said Franziska Neumann, study first author from the University of Freiburg in Germany. Based on the results, the researchers suggested that the additional use of the incense sticks during the vocabulary test may have promoted memory.

However, the scientists cautioned that cueing memory with odour during sleep might also have unseen side effects which could be assessed in future studies.

“Although there is evidence that cueing during sleep does not affect sleep quality, the question of potential side effects of cueing during sleep has not been sufficiently answered yet,” the researchers wrote in the study.

However, they said the study has practical everyday applications for enhancing learning during sleep.

“One particular finding beyond the seminal initial study was, that the fragrance also works when it is present all night. This makes the findings suitable for everyday use,” Kornmeier said.