Machine-learning algorithms require a huge amount of data to function, and the only information available for a scent comes from notoriously unreliable human noses and brains. (Even slight tweaks to a molecule can make a sweet, banana-scented compound reek of vomit; mysterious changes to your nose and brain, as many unfortunately learned from developing COVID-19, can make coffee smell of sewage.)

— Read more in Computers Are Learning to Smell at The Atlantic.