Most of us have heard of visual hallucinations i.e. seeing things that are not actually there. It is relatively lesser known that some people can experience something similar related to their sense of smell.
Smelling something foul (like an ashtray or burning hair) despite no source could mean that a person is affected by something known as phantom odor perception. New findings suggest that nearly 6.5 percent of Americans over the age of 40 have experienced it.
— Read more at What Is Phantom Odor Perception? at Medical Daily.