Scientists have identified molecules responsible for when good things smell bad and bad things smell good.
The sense of smell, thanks to covid, is probably having more of a moment than at any time since people carried posies to protect themselves from plague.
Anosmia was one of the signal features of OG covid, and later variants such as Delta. In fact, one recent study found that everyone infected with Delta experienced some loss of smell, even if they weren’t aware of it.
Parosmia, or a distorted olfactory function, is also a common and unfortunate feature of long covid – not only might scents lose their intensity, but once-pleasant smells such as coffee or perfumes or even chocolate can turn overpowering and unbearable. For some this can lead to food avoidance and poor mental health.
Your Back Page correspondent went through a phase like this after suffering smell loss from an unknown cause. Beloved perfumes smelt like industrial cleaning products and we had to beg colleagues to cover up their coffee cups as the smell made us gag.
Now a team has identified the precise molecular triggers of parosmia episodes involving coffee.
Using gas chromatography-olfactometry – a technique to separate out the volatile compounds in a vapour – they had parosmic subjects inhale vapour from instant coffee, describing each compound’s smell, its intensity and whether it elicited a parosmic reaction.
The parosmics were able to detect more than 30 different molecules, of which 18 triggered the reaction.
The most frequently reported trigger was 2-furanmethanethiol – this was described by non-parosmics variously with food terms such as coffee, “roasty”, popcorn and smoky, while parosmics struggled to find any reference points, and typically used words like “disgusting”, “repulsive” and “dirty”.
The authors say the study shows that it is not only incomplete perceptions of smells, while olfactory sensory neurons regenerate, that creates parosmia: “We have shown that a group of specific highly odour-active compounds are common triggers of distortion and individually elicit the perception of disgust, regardless of how many of the other aroma compounds are perceived at the same time.”
In a more sadistic experiment the press releases gloss over, the team also prepared a slurry using human faecal samples, to explore the oddity that people with parosmia “often comment that the smell of faeces is never as unpleasant as before, often smelling like other distorted foods, or more pleasant and biscuity, presenting the interesting corollary that foods smell of faeces yet faeces smell of food”.
Parosmic subjects did not find the sample foul-smelling, whereas the unfortunate “normosmic” they had sniff this mixture “scored the intensity of indole and skatole as close to the strongest imaginable”.
The key takeaway as far as The Back Page is concerned, therefore, is when a scientist comes towards you with a funnel and says “take a sniff of this”, run away.
If something isn’t passing the sniff test, send it as far as possible away from penny@medicalrepublic.com.au
