A new study co-authored by Professor of Psychology Andrew Ward suggests that a person's sense of smell may reveal a weight bias, one that is likely more pervasive than previously believed.

The study, which was first reported in the International Journal of Obesity, discovered that visual cues associated with overweight or obese individuals can influence a person's sense of smell.

"This is the first study to show that negative bias toward heavy individuals - something that is initially a visual experience - could transfer into an olfactory or smell experience," says Ward, who worked on the study with A. Janet Tomiyama and Angela Incollingo Rodriguez, both from UCLA.

In two related studies, the team of researchers showed subjects one of two sets of images. Both sets contained photographs of different people — half who were visibly overweight or obese, and half who were normal weight or thin — along with a series of distractor objects.

Each image was paired with a scent sample — a fragrance-free lotion (Eucerin) mixed with two drops of food coloring.

As each image appeared, the experimenter placed the scent sample under the participant's nose. Participants were instructed to rate each scent from 1 to 11. The more positive the rating, the more positive the reported smell.

The researchers found that when overweight or obese people were on the screen, participants gave worse ratings to the scent samples, despite the fact that the samples were unscented. Images of average-sized or thin people tended to trigger higher ratings.

While the researchers were surprised that weight bias could manifest through the sense of smell, the general stigma associated with obesity was not surprising.

"Studies have shown that people who are heavy are more stigmatized than 12 other historically stigmatized groups, including the homeless and those with mental illness," says Ward, who joined the Swarthmore faculty in 1997.

The study also discovered that the perceiver's body mass index (BMI) mattered. Participants with higher BMI tended to be more critical of heavier people, with higher-BMI participants giving scents a lower rating than lower BMI participants when scent samples were matched with an obese or overweight individual.

"It suggests that there isn't a 'self-enhancement' bias among people who are the target of the stigma," he adds.

The correlation between visual stimuli and sense of smell is well-established; previous research has connected the perception of foul odors to feelings of disgust.

"Right now, we only have a couple of ways to measure implicit attitudes, such as an implicit-association test measure," Rodriguez says. "We wanted to see if looking at something you find averse or unpleasant could influence how you evaluate a smell that has nothing to do with weight. This shows that something is happening implicitly, and we may have tapped into a new methodology for assessing people."

Ward believes that the study results highlight the consequences of weight stigma, which may be more widespread than previously believed.

"If you can show that weight bias can be present in olfactory areas, it opens up the question of how prevalent is weight bias," he says. "How much of our lives and experiences are being affected by this bias, perhaps unconsciously?"

Going forward, Ward hopes the methodology used in the study can be useful in identifying other forms of bias, not just weight.

"We may have developed a new method for uncovering unconscious bias in individuals that they would normally not be willing to admit."

Ward's study has been featured in numerous media outlets, including Fox News, Toronto's Globe and Mail, Business Insider, and Univison.