If you’ve caught COVID-19, there’s a fair chance you experienced strange disturbances to your sense of taste and smell: coffee smells like burning rubber, wine tastes like gasoline, and your once-favorite perfume makes you want to gag.  

Scientists at the University of Reading in the UK believe they may have discovered why certain food and drinks smell (and perhaps taste) disgusting to those who have experienced a distorted sense of smell (known as parosmia) after a viral infection.

According to the team, some of the most common food and drinks that set off parosmia include:

• Coffee

• Onions

• Garlic

• Chicken

• Green peppers. 

• Pungent smells like egg and mint/toothpaste are also often cited by many sufferers.

But what is it about these particular smells that make them so susceptible to being disturbed?

As reported in the journal Communications Medicine, the new study identified 15 different molecular triggers for parosmia. It appears that certain foods might be especially rich in these particular odor-active molecules that are prone to distortion.

To reach these findings, the team gathered people with 29 post-viral parosmia and 15 without parosmia, asking them all to undergo a sniffing experiment. As one of the most commonly cited “victims” of parosmia, the researchers chose the scent of freshly ground coffee as their prime subject.

Using gas-chromatograph olfactometry, they individually presented the different components of coffee's smell to the participants, who smelled each compound and describe them one by one.

From this, they could determine which components were prone to trigger the people with parosmia. They found that one aroma-producing compound in coffee – 2-furanmethanethiol – was particularly divisive. While the people without parosmia described it in pleasant terms – “coffee, roasty, popcorn, and smoky” – those with post-viral parosmia often perceived it as repugnant – describing it as “disgusting, repulsive, and dirty.”

Perhaps, certain food and drinks that smell bad to those with the condition are especially high in levels of these divisive compounds, the study argues. 

Another study published in June 2021 suggested that over 1 in 10 people who had COVID-19 reported having parosmia after the infection. Considering there have been hundreds of millions of documented COVID-19 cases, that's a lot of people who have experienced parosmia – yet we still know relatively little about how the virus affects our sense of smell. 

Off the back of the research, the team hopes to gain a deeper understanding of this curious symptom that has affected vast numbers of people worldwide since the COVID-19 pandemic hit. 

“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,” Dr Jane Parker, Associate Professor of Flavour Chemistry and Director of the Flavour Centre at the University of Reading, said in a statement.

“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,” explained Dr Parker.