The perception of smell, or olfaction, is the process of perceiving smell. Sense of smell occurs when an odor binds to a receptor within the nose, transmitting a signal to the olfactory system. The sense of smell has been deemed important to survival efforts. The loss of a sense of smell can result from some injuries or illnesses. The loss of smell has been gaining traction as an early indicator for some neurodegenrative diseases in research, and has been identified as an early symptom of COVID-19.