An olfactory hallucination (also known as phantosmia) is the detection or perception of a convincing imaginary smell that is not actually present in the person's environment.    This can occur in one or both nostrils. The specific hallucinatory odours perceived can vary from person to person and can vary depending on set and setting as well as the dosage taken. The smells themselves can range from pleasant to foul and are often described as being very odd and random in nature.
Olfactory hallucinations are often accompanied by other coinciding effects, such as external hallucinations, delusions, and gustatory hallucinations. They are most commonly induced under the influence of heavy dosages of hallucinogenic compounds, such as deliriants and psychedelics. However, they can also occur under the influence of stimulant psychosis and sleep deprivation.
- Distorted olfactory perception: A systematic review | https://www.tandfonline.com/doi/abs/10.3109/00016489.2012.659759?journalCode=ioto20
- Distortion of Olfactory Perception: Diagnosis and Treatment | https://academic.oup.com/chemse/article/27/7/611/324055
- Smelling things that aren't there (phantosmia) | https://www.nhs.uk/conditions/phantosmia/