Smells Like Clean Spirit

Occasionally you read a journal article so well-titled, you have to steal it for your blog post title. "Smells Like Clean Spirit" is a report by Rob Holland, Merel Hendricks, and Henk Aarts, in which they use smells to unconsciously modify their victims' participants' behavior.

In some ways, this research is nothing new. As the researchers point out, if we smell chocolate chip cookies, we may decide to eat; if we smell a garbage truck, we may walk faster down the street. We might associate pine scent with Christmas, or pheromones with sex. But most of these associations involve people being conscious of the odor and its impact. Holland's team wanted to demonstrate that scent could impact behavior even if people aren't conscious of it.

They created a "cleaning-related" odor in the office where they conducted their study by putting a citrus-scented cleaning liquid in a large bucket of warm water hidden behind a cubicle wall. Next, they asked volunteers to do a simple word-identification task where real words and nonsense words were flashed on a computer screen. Participants pressed a button when they saw the real words, and reaction time was measured. Half the time, the room was citrus-scented, and half the time, there was no scent. Here are the results:

Reaction times were significantly faster for cleaning words in the citrus-scented room, but not in the unscented room. Just six out of the fifty participants had even noticed the scent in the room, and none of them believed it had affected their performance. In a second experiment, in the same scented and unscented room, participants were simply asked to list what they were planning on doing that day. Thirty-six percent of participants in the scented room wrote something related to cleaning, while just eleven percent of people in the unscented room listed cleaning.

Finally, a new set of 22 college students was asked to fill out an unrelated questionnaire in a scented or unscented room. Next, they were moved to a different room and given a crumbly cookie to eat. Their eating behavior was captured by a hidden video camera, and then judges analyzed the video to see how frequently the students stopped to clean up the crumbs. Here are the results:

Apparently just smelling cleanser causes people to become tidier in their eating habits! Just one of the participants indicated being aware of the cleaning smell, and when those results were excluded from the analysis, the effect remained. None of the participants even said they were thinking about cleaning while they ate their cookie.

Holland's team claims that this is the first research showing a nonconscious relationship between odor perception and cognition and behavior. Other studies have found similar effects for visual phenomena (such as walking slowly after seeing pictures of elderly people), but not for smell.

Holland, R.W., Hendriks, M., & Aarts, H. (2005). Smells like clean spirit: Nonconscious effects of scent on cognition and behavior. Psychological Science, 16(9), 689-693.