Why do I smell something nobody else does?

Hello. Thank you for posting.

I can give you some general information. If you are concerned, see your doctor.   Some people have a heightened sense of smell.  Hyperosmia is an increased olfactory acuity (heightened sense of smell), usually caused by a lower threshold for odor. This disorder arises when there is an abnormally increased signal at any point between the olfactory receptors and the olfactory cortex. This is different than smelling things that are not there.   

Brief episodes of phantom smells or phantosmia – smelling something that's not there – can be triggered by temporal lobe seizures, epilepsy, or head trauma. Phantosmia is also associated with Alzheimer's and occasionally with the onset of a migraine.

A runny nose is usually associated with a cold or allergies. The terms "rhinorrhea" and "rhinitis" are often used to refer to a runny nose. Strictly speaking, rhinorrhea refers to a thin, relatively clear nasal discharge. 

Helena