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Olfactionthe is not a recognized term in scientific literature. For clarity, this article uses olfaction, the sense of smell, to describe the topic more widely understood by researchers and readers.

Olfaction refers to the detection and processing of volatile odorant molecules by the nervous system. Odorants dissolve in mucus in the nasal cavity and bind to receptors on the cilia of olfactory receptor neurons. Humans possess hundreds of different olfactory receptor types, enabling combinatorial coding that allows the discrimination of a vast array of odors from a relatively small set of receptors. Activation of these receptors triggers intracellular signaling that generates electrical impulses carried by the olfactory nerve to the olfactory bulb.

From the olfactory bulb, signals project to higher brain regions, including the piriform cortex, amygdala, and entorhinal cortex, with some pathways also reaching the orbitofrontal cortex. This network supports both the perception of odor and its emotional and memory associations, as odor information is closely linked to the limbic system. Olfactory processing contributes to flavor perception, especially when odor information reaches the brain retronasally during eating.

Olfactory neurons are unusual in that they are continually renewed by basal stem cells, allowing ongoing turnover throughout life. Genetic variation in olfactory receptor genes underlies differences in odor perception among individuals and populations.

Clinically, impaired olfaction—anosmia or hyposmia—can result from infections, head trauma, aging, or neurological disease. Diagnosis often involves standardized smell tests, and rehabilitation may include olfactory training. Olfaction plays a critical role in nutrition, safety, and social signaling across many species, though its prominence and specialization vary widely in the animal kingdom.