Anosmia is the inability to smell or have olfactory sensation. You can remember this by noting the prefix 'a' typically signifies the absence of something which is followed by 'nos' as in nose. Individuals suffering from anosmia can't sense odors. This can affect the way things taste as well as sometimes be dangerous (such as not smelling smoke or leaking gas). Anosmia can be temporary and be caused by nasal congestion, colds, or some medications. Anosmia can also unfortunately be permanent and be caused by head injury or neural disease such as Parkinson's or Alzheimer's.