What’s your favorite smell? Is it the whiff of freshly ground coffee in the morning or blossoms in spring? Whatever it may be, imagine a world where this sense is distorted and sometimes disturbing. This is the reality for people living with parosmia, a disease that can turn the smell of freshly baked cookies into burning garbage.

It was a mystery why certain food and drinks smell or taste horrible for people with parosmia. Some medical professionals assumed it was all in the individual’s head. However, a recent study from a team at the University of Reading has uncovered some molecular triggers behind the disorder, presenting a solid scientific case for what causes it.

Using a technique called gas chromatography, the team trapped and separated the aromas that comprise coffee. Next, the compounds were smell-tested on a group of volunteers with parosmia who were asked to identify which odors were triggering the sense of disgust. The scientists were able to identify 15 odor compounds that cause an unpleasant smell, including the most potent aroma molecule in coffee, 2-furanmethanethiol.

“This is solid evidence that it’s not all “in the head”, and that the sense of disgust can be related to the compounds in the distorted foods. The central nervous system is certainly involved as well in interpreting the signals that it receives from the nose. The parosmic experience is a combination of the two mechanisms which produces the distorted perception of everyday foods, and the associated sense of disgust,” explains the author of the study Dr. Jane Parker.

They continue: “We can now see that certain aroma compounds found in foods are having this particular effect. It will, we hope, be reassuring for those with parosmia to know that their experience is “real”, that we can identify other foods which may also be triggers and, moreover, suggest “safe” foods that are less likely to cause a problem. This research provides useful tools and strategies for preventing or reducing the effect of the triggers,” says Parker.

The recent Covid-19 pandemic has resulted in a lot more of the population suffering from the previously rare smelling disorder. 50 to 60 percent of people infected with the virus lost their sense of taste and smell, with around 10 percent of these going on to develop parosmia. This huge increase in the number of people suffering from the smell issues has triggered an increased awareness and funding for researching the disorder.

The team hopes to gain further insight into the exact mechanisms behind the disease, planning to do further research to uncover exactly what is happening in the nerves and their receptors to trigger these disturbing smells.

Source study: Communications Medicine – Insights into the molecular triggers of parosmia based on gas chromatography olfactometry