Odorants

Odorants are volatile chemical compounds that can elicit odor perception when inhaled and interact with the olfactory system. They are detected by sensory neurons in the nasal cavity and interpreted by the brain.

In mammals, olfactory receptor neurons express a large family of G protein-coupled receptors. Each odorant can bind to multiple receptors, and each receptor can respond to several odorants, creating a combinatorial code that encodes odor identity. Binding triggers intracellular signaling, leading to neuronal firing that travels to the olfactory bulb and onward to higher brain regions.

Odorants are chemically diverse, including terpenoids, esters, aldehydes, ketones, and sulfur- or nitrogen-containing compounds. They can be natural, such as limonene in citrus or vanillin in vanilla, or synthetic, used as fragrance ingredients. Detection thresholds vary widely and are influenced by volatility, polarity, and receptor affinities, among other factors. Some odorants act as pheromones in certain species, while others primarily contribute to flavor and aroma.

Odorants are commonly evaluated with olfactometry and expressed in metrics such as odor units or odor activity values to estimate perceived strength in mixtures. They underpin the flavor and fragrance industries, environmental odor assessment, food science, and safety testing. Certain odorants can irritate the respiratory system at high concentrations, highlighting the importance of dose and context in exposure.

The study of odorants integrates chemistry, neuroscience, and sensory science to understand how molecular structure relates to perception and how complex olfactory experiences arise from receptor activation patterns.

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