An olfactory hallucination, known as phantosmia, makes you detect smells that aren't in your environment.

The odors you notice in phantosmia are different from person to person and may be foul or pleasant. You may notice the smells in one or both nostrils. The phantom smell may seem to always be there or it may come and go.

Phantosmia may be caused by a head injury or upper respiratory infection. It also can be caused by aging, trauma, temporal lobe seizures, inflamed sinuses, brain tumors, certain medicines and Parkinson's disease. Phantosmia also can result from a COVID-19 infection.

Talk to your healthcare professional if you have symptoms of phantosmia. Your care professional can rule out any serious conditions that may be causing olfactory hallucination.

Parosmia is another smell disorder that's similar to phantosmia. But in parosmia a smell that's present in your environment is changed and doesn't smell as it typically would. Parosmia can occur with damage to the olfactory system. This can happen after a serious respiratory infection, including COVID-19.