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Scientific review

Why can the same scent smell different?

Smell does not passively record a molecule. What we perceive is shaped by receptor activation, concentration, familiarity, language, and individual biology.

Contents

  1. 01How receptors create a code
  2. 02Why a constant scent becomes less noticeable
  3. 03How genes and experience create differences
  4. 04What population differences can tell us

The central question

What comes from the molecule, and what from the person smelling it?

A molecule establishes physicochemical possibilities, but it does not carry one finished perceptual label. Each odorant can activate more than one receptor, and each receptor can respond to more than one odorant. Odour identity emerges from the overall pattern. [1]

That pattern can change with concentration. Familiarity and the words we use then influence how we recognise and describe the odour. Across tests of hundreds of molecules, variation between people was substantial, and familiarity influenced the precision of their descriptions. [1][2][3]

Perception also changes within one person. Continuous exposure reduces the response to a stable stimulus, while age, nasal conditions, smoking, and particular genetic variants can affect different aspects of olfactory function. [4][5][6][7]

Five findings that explain differences in olfactory perception

The evidence does not make smell arbitrary. It identifies the biological and cognitive stages that create predictable variation.

  1. 01

    Odours are encoded combinatorially

    Odour quality arises from an activation pattern, not one exclusive receptor for every smell. [1]

  2. 02

    Concentration can change quality

    The same molecule at a different concentration can recruit a different receptor combination and produce a different impression. [1]

  3. 03

    Adaptation begins early

    A reduced response after sustained or repeated exposure already appears in olfactory sensory cells. [4]

  4. 04

    One gene can alter the perception of one molecule

    OR5AN1 variants were associated with detection threshold and intensity differences for particular musk molecules, not a general preference for every musk scent. [5]

  5. 05

    Group differences are tendencies, not identities

    Age and smoking correlate with olfactory function at the population level, while average sex differences found in meta-analysis were small. [6][7][8]

Read the evidence

From molecule to experience

Four levels that make olfaction personal

Olfactory experience begins in the nose but does not end there. Each stage transforms the signal it receives.

How receptors create a code

The olfactory system does not receive a finished odour identity. Information is encoded as a combination of activated receptors.

A code formed by many receptors

Malnic et al. (1999) showed that different compounds activate different combinations of olfactory receptors. One receptor can respond to several molecules and one molecule to several receptors. This allows a finite receptor repertoire to encode an enormous range of stimuli. [1]

Small changes in structure or concentration can alter this pattern. Perceived odour therefore depends not only on the presence of a molecule, but also on which receptors respond and how strongly they are activated. [1]

Description depends on familiarity

Keller and Vosshall (2016) studied perception of 480 molecules and recorded substantial variation between participants. Familiarity supported more specific descriptions, while unfamiliar odours received more generic labels. [2]

In a cross-cultural study, Ferdenzi et al. (2017) found that cultural background and the presence of an odour label affected responses to the same stimuli. Supplying a name reduced some cultural differences. [3]

Why a constant scent becomes less noticeable

Adaptation changes the olfactory response while a stimulus continues or is repeated.

The response falls at the sensory cell

Kurahashi and Menini (1997) showed that adaptation begins in the olfactory receptor cell itself. After sustained or repeated stimulation, transduction mechanisms temporarily reduce the response to a following stimulus. [4]

In this experiment, the principal mechanism occurred downstream of cAMP production and involved calcium feedback on cAMP-gated channels. The study concerned sensory cells and did not investigate changes in central neural networks. [4]

What olfactory adaptation does not measure

Adaptation is a change in the response of the sensory system. An odour becoming less noticeable to one person is not a measurement of its airborne concentration and does not show that the source has stopped releasing molecules. [4]

How genes and experience create differences

Personal olfaction is neither exclusively genetic nor exclusively learned.

Genetic effects concern particular molecules

Sato-Akuhara et al. (2023) examined variants of the OR5AN1 receptor. Variants responded differently to macrocyclic and nitro musks in cell assays and were associated with differences in muscone detection threshold or the perceived intensity of particular molecules. [5]

The effect was not uniform across every molecule and did not necessarily concern pleasantness. In that study, genetic variation changed the intensity of some stimuli without consistently predicting how pleasant participants found them. [5]

Labels and familiarity change evaluation

The same odour can be evaluated differently when its label or familiarity changes. This does not make chemistry unimportant. It means perception emerges from the interaction between the chemical stimulus and prior knowledge. [2][3]

What population differences can tell us

Averages describe probabilities. They do not precisely describe every person.

Age changes more than one stage

Kondo et al. (2020) describe an increase in olfactory dysfunction from age 60 and changes in both the olfactory epithelium and central processing. Age effects vary substantially between individuals and do not mean that every older person experiences the same decline. [6]

Nasal conditions and viral infections can also affect the access of molecules to receptors or the function of the olfactory system. These are changes in olfactory function, not simple differences in preference. [6]

Associations need their true scale

Ajmani et al. (2017) found that current smokers had higher odds of olfactory dysfunction than never-smokers, while former smokers did not differ statistically. This is a population association and does not predict one person’s course. [7]

Sorokowski et al. (2019) found that women performed better on average in threshold, discrimination, and identification tests, but effect sizes were small. Individual variation is much greater than the phrase “women smell better” suggests. [8]

Evidence boundaries

What should not be inferred about one person

Olfaction contains measurable tendencies and considerable individual variation at the same time.

  1. 01

    One gene does not explain a whole fragrance

    Known associations concern particular receptors and molecules. They are not enough to predict the perception of a finished fragrance mixture.

  2. 02

    Intensity is not pleasantness

    Someone may detect a compound at a lower concentration without finding it more or less pleasant.

  3. 03

    Adaptation does not prove that scent has vanished

    A reduced sensory response does not measure airborne concentration or the amount released by the source.

  4. 04

    Averages do not describe every person

    Age, sex, and smoking are associated with average population differences in olfactory function. None of these factors determines one person’s ability by itself.

05

Synthesis

Olfaction is a shared mechanism and a personal experience

We all use the same basic architecture: volatile molecules, olfactory receptors, combinatorial patterns, and neural processing. Within that shared system, concentration, genes, age, adaptation, and experience shift the final perception. [1][4][5][6]

Personal perception does not negate the chemical stimulus. It explains why the intensity or description of the same odour can change with concentration, familiarity, and individual biology. [1][2][3][5]

Questions raised by the evidence

Frequently asked questions about the sense of smell

Does everyone perceive the odour of a molecule in the same way?

Not always. Receptor activation follows shared principles, but genetic variation, concentration, and familiarity can alter intensity or description. [1][2][5]

Why do we stop noticing a steady scent?

Olfactory adaptation temporarily reduces the response to continuous stimulation. This study located the principal mechanism in cellular signal transduction. [4]

If I no longer smell it, has it left the air?

Not necessarily. Adaptation shows that your olfactory response has decreased. It does not measure airborne concentration or prove that the source has stopped releasing molecules. [4]

Can genes alter how a fragrance is perceived?

They can alter sensitivity to particular molecules. OR5AN1 variants have been linked to threshold and intensity differences for certain musk molecules, not a general preference for an entire fragrance family. [5]

Does smell change with age?

At the population level, olfactory dysfunction becomes more common from age 60. Individual trajectories vary substantially and reflect many biological and environmental factors. [6]

Is there a large olfactory difference between women and men?

Meta-analysis found a small average advantage for women in several tests. Effect sizes were small, so individual variation remains much larger than the mean group difference. [8]

Methodology note

This review combines receptor research, perception experiments, and meta-analyses of population differences. Population associations are not used as diagnoses or predictions for individuals.

Genetic statements remain limited to the receptors and molecules tested. The adaptation study concerns the mechanism of sensory response and does not measure airborne odorant concentration or the operation of a fragrance source.

The foundational combinatorial-coding study tested individual compounds in mouse olfactory neurons. It supports a coding mechanism, but it was not a human sensory test of finished fragrance mixtures.

The human studies used defined samples and stimuli: 55 participants and 480 molecules at two concentrations in Keller and Vosshall, six odours tested with participants from France and Quebec in Ferdenzi et al., and specific musk molecules in the OR5AN1 study. Their results do not predict every person’s experience or every complex fragrance.

References

  1. Malnic, B., Hirono, J., Sato, T., & Buck, L. B. (1999). Combinatorial receptor codes for odors. Cell, 96, 713–723.
  2. Keller, A., & Vosshall, L. B. (2016). Olfactory perception of chemically diverse molecules. BMC Neuroscience, 17, 55.
  3. Ferdenzi, C., Joussain, P., Digard, B., et al. (2017). Individual differences in verbal and non-verbal affective responses to smells: Influence of odor label across cultures. Chemical Senses, 42, 37–46.
  4. Kurahashi, T., & Menini, A. (1997). Mechanism of odorant adaptation in the olfactory receptor cell. Nature, 385, 725–729.
  5. Sato-Akuhara, N., Trimmer, C., Keller, A., et al. (2023). Genetic variation in the human olfactory receptor OR5AN1 associates with the perception of musks. Chemical Senses, 48, bjac037.
  6. Kondo, K., Kikuta, S., Ueha, R., Suzukawa, K., & Yamasoba, T. (2020). Age-related olfactory dysfunction: Epidemiology, pathophysiology, and clinical management. Frontiers in Aging Neuroscience, 12, 208.
  7. Ajmani, G. S., Suh, H. H., Wroblewski, K. E., & Pinto, J. M. (2017). Smoking and olfactory dysfunction: A systematic literature review and meta-analysis. Laryngoscope, 127, 1753–1761.
  8. Sorokowski, P., Karwowski, M., Misiak, M., et al. (2019). Sex differences in human olfaction: A meta-analysis. Frontiers in Psychology, 10, 242.