Olfactory disorder: A loss in the ability to smell or a change in the way odors are perceived. Reduction of the sense of smell is termed hyposmia. Total inability to detect odors is termed anosmia. As for changes in the perception of odors, some people notice that familiar odors become distorted. Or, an odor that usually smells pleasant instead smells foul. Still other people may perceive a smell that is not present. (An olfactory hallucination is one that involves the sense of smell.)
Smell disorders have many causes. Most people who develop a smell disorder have recently experienced an illness or an injury. Common triggers for smell disorders are colds and other upper respiratory infections and head injuries. Among other causes of smell disorders are polyps in the nasal cavities, sinus infections, hormonal disturbances, or dental problems. Exposure to certain chemicals, such as insecticides and solvents, and some medications have also been associated with smell disorders. People with head and neck cancers who receive radiation treatment are also among those who experience problems with their sense of smell.
Smell disorders can have serious consequences. The sense of smell often serves as a first warning signal, alerting us to the smoke of a fire or the odor of a natural gas leak and dangerous fumes. Perhaps more important is that our chemosenses are sometimes a signal of serious health problems. Obesity, diabetes, hypertension, malnutrition, Parkinson's disease, Alzheimer's disease, multiple sclerosis, and Korsakoff's (alcoholic) psychosis are all accompanied or signaled by chemosensory problems such as smell disorders.