Sweaty herring, which one stinks more?

Text｜Xu Rui

(Copyrighted image from the gallery, no permission to reprint)

People from all cultures dislike the smell of isovaleric acid, a smell that comes from sweaty feet.

The rotten egg smell of fermented herring has been described as the world's most disgusting smell, but it's a favorite among the Swedes, and black liquorice, which some people find disgusting, is a favorite among the Dutch.

Scientists have long believed that culture is a driving force behind this smell preference. However, a new study published in Current Biology suggests that odor pleasantness is primarily a personal preference, with the chemical composition of odor molecules dictating our sense of smell.

“The pleasantness of smells is reflected in the structure of the compounds we smell,” says Noam Sobel, a neurobiologist who studies olfaction at the Weizmann Institute of Science in Israel. The new study confirms that pleasant smells “are not only universal across cultures, but also across animals.”

Asifa Majid, a cognitive scientist at the University of Oxford in the UK, has been thinking about the connection between culture and smell since 2018. She and her colleagues compared the sense of smell of the Kahai people, a primitive tribe in Malaysia, with that of Dutch volunteers. She said that although the two groups used different words to describe the same bad smell, "they made the same disgust expression."

To understand whether this "disgust" is universal, Majid and his colleagues recruited 225 participants from nine cultural backgrounds, including hunting tribes in Malaysia and northern Mexico, farmers in Ecuador, and urban residents in Thailand. They chose these groups because some of them have little contact with Western food, perfume, etc.

The researchers had the participants smell 10 substances with specific odors in random order and asked them to rank the odors from most to least pleasant. The results were compared with similar tests conducted on residents of New York in 2016.

On average, people from all cultures in the study had similar odor preferences. Most people rated vanilla as the most pleasant, followed by ethyl butyrate (a fruity odor associated with ripe bananas and nectarines), and then linalool (common in floral scents). Diethyl disulfide (the odor of garlic and durian) and isovaleric acid (a rancid odor associated with some cheeses or sweaty feet) tended to rank last.

But some participants ranked the smells differently. For example, isovaleric acid was the first choice for a few participants.

When they looked for drivers of these differences through statistical analysis, the researchers found that 54% of the variation in odor pleasantness could be attributed to personal choice, with just 6% attributable to culture.

"In general, the perception of relatively good and relatively bad things is shared across populations," Majid said. This may come down to chemistry. No matter who smells a substance, the structure of its odor molecules is the same. Therefore, humans will biologically respond to it in the same way.

Sobel noted that the new study had relatively fewer participants and odor source substances than previous studies, but it surveyed more cultural groups, which gives it value.

"I think the results are credible," Sobel said. The new findings confirm that there is a fundamental connection between the molecular structure of odors and people's evaluation of odors, but this does not mean that acquired learning and experience accumulation will not change people's perception.

Majid believes that language and culture are still useful in people's olfactory preferences. For example, the smell of Parmesan cheese and stinky feet both contain isovaleric acid. But people like the former far more than the latter.

“The smell hits you, but (people’s response to it) can be changed,” Majid said.

Related paper information:

https://doi.org/10.1016/j.cub.2022.02.062

China Science Daily (2022-04-15 2nd edition International)

Editor | Zhao Lu

Typesetting | Zhihai