is a condition in which the natural smell sensation is altered and is converted into an unpleasant smell. Repeated upper respiratory tract
infections, exposure to some harmful chemicals etc are usually some possible causes that damage the nerve
cells that perceive smell sensation to brain(olfactory neurons). But there may be some psychological causes also. So, a firm diagnosis has to be established using some investigations like Pennsylvania Smell Identification Test. I suggest to consult a neurophysician.
Hope it helps!