What happened to my sense of smell?

Episode Summary

Executive Summary: This episode of BBC CrowdScience explores why smells affect people so differently, using the pungent titan arum as a starting point. It explains how odor molecules activate receptors and patterns in the brain, why genetics and learning shape preferences, how COVID can disrupt smell, and why smell training may help recovery. The episode concludes that smell is complex, subjective, and more important than most people realize.

Main Topics: The titan arum and the science of stink: The episode opens with the corpse flower’s intense odor, explaining how its rotting-flesh smell attracts carrion flies and beetles for pollination, and how subjective reactions to that smell vary. How smell perception works: Experts explain that odor molecules must be volatile to reach the olfactory cleft, bind receptors, and create neural patterns the brain interprets as smell. Why smells feel different to different people: The program explores how genetics, receptor variation, and learned associations make some odors pleasant to one person and nauseating to another. COVID-related smell loss and recovery: The episode discusses how coronavirus can damage smell, the prevalence of smell loss, and evidence that smell training can aid recovery over time. Collecting and recreating odors: Smell artist-scientist Sissel Tolaas demonstrates capturing odors around the world, analyzing them chemically, and reconstructing them for artistic and research purposes. Predicting odor pleasantness: Neurobiologist Noam Sobel describes work showing that while people generally agree on many smells, research is beginning to predict whether a novel odor will seem pleasant or unpleasant.

Key Arguments: Smell is not just about odor molecules; the brain interprets complex receptor patterns as specific experiences. Genetic differences in odor receptor genes can make some people unable to detect particular smells at all. Learned associations strongly influence smell perception, so different people may use the same word for different odor experiences. COVID-19 can disrupt smell by affecting supporting cells around receptors, and in some cases potentially deeper neural structures. Smell training—repeated daily exposure to selected odors—can help restore olfactory function after viral loss. Most people agree on the pleasantness of many odors, and strong disagreements are the exception rather than the rule.

Data Points: Titan arum bloom frequency: About once every 10 years - Described by Kew Gardens staff as the plant’s rare flowering cycle Titan arum bloom duration: 2 days - The corpse flower only blooms briefly when it flowers COVID-related smell loss prevalence: Up to 60% - Reported rate of smell/taste loss in infected people Number of human odor receptors: Around 400 - Estimated receptor types in the human nose Possible odorants detectable: Possibly as many as a trillion - Illustrates the enormous combinatorial capacity of the olfactory system Rose compounds: Up to 275 distinct compounds - Example of how complex natural odors can be Smell training daily exposure: 20 to 30 seconds each smell - Recommended duration for each odor in the training routine Smell training study period: 3 months - Early studies showing improvement after sustained training Annual participant volume: Around 2,000 people a year - Noam Sobel’s lab tests people to compare odor pleasantness Odor cabinet size: Close to 1,000 odorants - Used to study agreement in pleasantness judgments Agreement rate: Very high agreement on 900 of 1,000 molecules - People largely agree on odor pleasantness in Sobel’s experiments

Pivotal Quotes: "The current working theory around the damage it causes is that the virus is infecting the supporting cells around the smell receptors..." — Professor Carl Philpott: Explaining how COVID-19 can cause smell loss "I use essential oils of rose, clove, eucalyptus, and lemon. I put them onto like a piece of cotton wall pad and put them inside jars..." — Patient describing smell training: Demonstrating the practical method used to retrain smell after loss "You can imagine it, maybe one example is to think about reading... That’s how you can imagine that odors work." — Professor Thomas Hummel: Explaining the combinatorial coding of odors by receptors

Implications: Smell is a highly complex, partly trainable sense shaped by biology and experience. The findings matter for COVID recovery, clinical smell disorders, perfumery, and product design, while reminding listeners not to take their sense of smell for granted.