Is Smell the Inferior Sense? Olfaction, Memory, and Parkinson's Clues | The Rest Is Science

In this episode of The Rest Is Science, Hannah Fry and Michael Stevens investigate whether smell is the inferior sense and how odors shape our perception and memory. The hosts discuss how we notice scents, the limitations of human olfaction, and how animals excel at smelling when given the chance. Through engaging stories—from everyday candle scents in a home to the gas odorant ethyl mercaptan and a remarkable Parkinson’s smell-detection case—the episode reveals how scents influence behavior, memory, and even disease diagnostics. The discussion blends quirky anecdotes, classic olfactory science, and practical implications for health and everyday life.

Overview

The Rest Is Science episode centers on smell, a sense often labelled inferior, and asks how true that label is. Co-hosts Hannah Fry and Michael Stevens discuss their own experiences of odor in ordinary environments and imagine what scents might be like if we could quantify them as precisely as sight or sound. They use everyday examples, such as a faint candle in a room or the aroma of a holiday trip, to ground a discussion that spans neuroscience, evolution, and perception.

The Perceptual Power of Smell

The episode covers how the olfactory system differentiates countless odors and how humans can detect minute chemical differences, sometimes at parts-per-trillion levels, but often fail to attend to smells unless there is a strong cue. They describe the difference between sensing a smell and consciously locating its source, noting that our brains do not construct a reliable “odor map” the way they do with vision or audition. The science is connected to a broader claim: we notice smells more when they matter for survival or memory than for routine navigation through space.

Attention, Adaptation, and Change Blindness in Smell

A key theme is attention. The hosts discuss change anosmia, adaptation, and olfactory fatigue, explaining why we frequently miss odors unless they shift or intensify. They compare this to how we reliably notice visual or auditory changes and point to the brain’s economy in processing olfactory data, which often remains non-conscious until it becomes salient.

Real-World Smell vs Lab Smell

Several anecdotes illustrate the gap between laboratory conditions and real-life environments. The discussion includes how dogs outperform humans in locating odors in controlled experiments, yet struggle in the field when contexts vary. A famous case about cling film training demonstrates how dogs can learn to smell a particular containment, but humans often overgeneralize or misinterpret a scent without proper context.

Joy Milne and the Parkinson’s Smell

A standout story is Joy Milne, a remarkable “super smeller” who consistently detected a distinctive odor associated with people who would develop Parkinson’s. The hosts recount the early observations, the subsequent experimental validation, and the potential for smell-based diagnostics and electronic noses to transform disease detection.

The Social and Behavioral Dimensions of Olfaction

The episode links deodorant preferences to the body’s own scent, suggesting our non-conscious drives shape everyday choices. It also discusses how visual cues can bias olfactory perception, such as color altering flavor judgments, highlighting the dominance of vision in how we interpret smells and flavors.

Implications for Health, Memory, and the Future

Throughout, the conversation hints at broader implications: the possibility of smell-based diagnostics, non-invasive screening, and the evolving role of olfaction in medicine and personal care. The show invites listeners to consider how much of our scent world operates beneath conscious awareness and what future technologies might reveal about our own noses.

Conclusion

In closing, the hosts remind us that the inside of our noses has a smell that we cannot consciously identify, and that this non-conscious scent world can influence behavior and well-being even if we rarely notice it. The episode ends with an invitation to curiosity and to question the long-standing notion that smell is inherently inferior.