Anosmia is a condition in which people have no sense of smell. It can be caused by a variety of factors, from temporary blockage of the nose by a sinus infection to head trauma. While this condition might seem irritating, but ultimately trivial, anosmia can actually have a profound effect on someone's life. People with anosmia often experience ageusia, the inability to taste, because smell plays such an important role in taste perception. They are also put at risk by their inability to smell spoiled food and gas leaks, among other dangers which are often readily noticeable to people with an intact sense of smell.
There are a number of conditions related to anosmia. Hyperosmia, for example, is an extremely sensitive sense of smell, while parosmia causes people to misinterpret smells, detecting something unpleasant when the odor is neutral or nice. In phantosmia, people detect smells where there are none, in a sort of olfactory hallucination.
In some cases, anosmia is purely temporary. Many of us have endured a temporary decline in sense of smell with a big cold or sinus infection, for example, and when the nose clears again, the sense of smell returns. At other times, the condition is caused by a blockage in the nose which requires medical attention, such as a tumor. Head trauma can also damage the sense of smell, as can some illnesses.
When anosmia is congenital, it means that someone was born without a sense of smell. Congenital anosmia can be difficult to diagnose, because it may take some time for a child to realize that he or she is missing out on a vital sense, and parents may not catch on when a child is preverbal. Acquired anosmia has an onset later in life.
Sometimes anosmia takes an unusual form: in specific anosmia, someone is unable to detect certain smells, but he or she can smell everything else without difficulty. Specific anosmia seems to have a genetic component, although people can also become desensitized to particular odors through prolonged exposure.
To diagnose anosmia, doctors use familiar odors and either waft them up the nose, or ask patients to use scratch-and-sniff cards. If the patient has difficulty detecting or identifying the odors, he or she is considered to be afflicted with anosmia. Once the condition is diagnosed, getting to the cause is important, to ensure that the patient receives the appropriate treatment.