Impairment of the sense of smell and taste are commonly associated with aging but can also occur in younger people due to a wide variety of causes.
Further information: Olfaction Disorders of olfaction
There are various olfactory disorders:
1. Anosmia – inability to smell
2. Dysosmia – things smell different than they should
3. Hyperosmia – an abnormally acute sense of smell.
4. Hyposmia – decreased ability to smell
5. Olfactory Reference Syndrome – psychological disorder which causes patients to imagine they have strong body odor
6. Parosmia – things smell worse than they should
7. Phantosmia – “hallucinated smell”, often unpleasant in nature
Source: http://en.wikipedia.org/wiki/Disabilities#Olfactory_and_gustatory_impairment
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