Sense of smell (also known as olfaction) is the ability to detect and perceive odors through specialized sensory cells called olfactory receptor neurons located in the olfactory epithelium high in the nasal cavity. When odorant molecules (volatile chemicals) enter the nose during inhalation, they bind to receptors on these neurons, triggering electrical signals that travel via the olfactory nerve (cranial nerve I) directly to the olfactory bulb in the brain, then to regions like the piriform cortex, amygdala, and orbitofrontal cortex for processing, identification, emotional response, and memory association. It plays a key role in detecting food safety (spoiled or toxic substances), environmental dangers (smoke, gas leaks), social cues (pheromones in some species, though less prominent in humans), and enhancing taste perception (much of what we perceive as “flavor” comes from retronasal olfaction when aromas travel from the mouth to the nose). The human sense of smell can distinguish thousands of different odors, though sensitivity varies widely between individuals and declines with age, illness, smoking, or exposure to toxins; complete or partial loss (anosmia or hyposmia) can occur from viral infections (e.g., common cold or COVID-19), head trauma, sinus disease, neurological conditions, or aging.