Practical insights

Practical insights 2 min

Adaptation 2 min

We quickly adapt to individual smells, sometimes within 200ms¹⁰², meaning that we might not notice a certain smell after it has been present for a certain amount of time. When incorporating smells into experiences, it might be helpful to plan for periodic changes.

Sensitivity 2 min

Human noses can distinguish thousands of odorants at very low concentrations, though individual sensitivity varies greatly. It was traditionally thought that humans could distinguish around 10,000 odours, but new research exploring combinations of odours puts this figure much higher, at more than a trillion¹⁰³. Surprisingly though, despite this sensitivity in distinguishing between smells, naming them appears to be something that many people find difficult in the absence of additional context from the other senses.

Context 2 min

Odour perception depends on context, temperature and humidity. A subtle scent in an open-air environment may become overwhelming in a confined space. In addition, higher temperatures increase the volatility of odour molecules, making smells stronger. Low humidity dries out the nose whilst high humidity slows evaporation of odour molecules, both of which are likely to degrade odour perception¹⁰⁴.

A well-known example of how context shapes odour perception comes from a neuroimaging study¹⁰⁵ where a cheese-like odour was presented to participants under the label cheddar cheese or body odour. This labelling strongly impacted how the brain responded to the odour, in regions linked with emotional processing and odour processing. In addition, people's perception of the pleasantness of the odour fell sharply when the label read* body odour compared with cheddar cheese*. In another classic experiment¹⁰⁶, researchers took five chemically ambiguous odours and paired them with positive or negative descriptions, then asked participants to rate them. These included pine oil (paired with* Christmas tree vs spray disinfectant)*, menthol (breath mint vs chest medicine), violet-leaf (fresh cucumber vs mildew) and patchouli oil (incense vs musty basement). Alternative labels swung pleasantness ratings by 1-3 points on a nine-point scale, again illustrating the significant importance of context in our odour experiences.

Current technical challenges 1 min

Current chemical-release systems are often expensive, rely on scent vials that need to be replaced regularly, and are limited in terms of the number of vials that can be handled (limiting the number of smells that can be released). Controlling the scent diffusion is also problematic: odours frequently linger long after their intended moment, which can be impactful when multiple people are doing different experiences in a confined area.