odours

An odour, in British English, is a smell or scent perceived when volatile chemical compounds interact with the olfactory system. Odours are produced by odourants released by sources such as foods, flowers, or industrial processes. The perception of an odour depends on concentration, volatility, composition, and the listener's physiology and experience. Odours differ from flavours because they are detected by the nose rather than the tongue, though they contribute to overall flavour when combined with taste and trigeminal sensations.

Detection and perception: Odourants reach the olfactory epithelium in the nasal cavity during inhalation. They bind to olfactory receptors on olfactory receptor neurons, which are G-protein-coupled receptors. Each receptor can bind several odourants; each odourant can activate multiple receptors, creating a combinatorial code that differentiates thousands of smells. Adaptation reduces sensitivity with continuous exposure. The sense also involves the olfactory bulb and higher brain regions, linking smells to memories and emotions.

Measurement and terminology: The strength or concentration of an odour is assessed in units such as odour units (OU) or odour concentration, often via dynamic olfactometry. Odour thresholds vary between compounds and individuals, leading to subjective impressions. Hedonic tone describes whether an odour is perceived as pleasant or unpleasant; cultural and individual factors influence judgments. Anosmia is loss of smell; phantosmia is smelling odours that are not present.

Applications and regulation: Odour measurements support environmental monitoring, industrial odour management, and health and safety in workplaces. In licensing and planning, communities consider odour nuisance. In science, research on olfaction informs perfume development, flavour science, and neuroscience.