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.

Why do I smell something bad but no one else does?

An olfactory hallucination (phantosmia) makes you detect smells that aren't really present in your environment. The odors detected in phantosmia vary from person to person and may be foul or pleasant. They can occur in one or both nostrils. The phantom smell may seem to always be present or it may come and go.

What does it mean when you smell something rotten?

Phantosmia (phantom smell), also called an olfactory hallucination or a phantom odor, is smelling an odor that is not actually there. It can occur in one nostril or both. Unpleasant phantosmia, cacosmia, is more common and is often described as smelling something that is burned, foul, spoiled, or rotten.