Experts are warning Birmingham residents of phantosmia - a medical term for smelling odours that aren't there.
Phantosmia may sound like it poses no real health risk, but it could in fact be a red flag for serious medical conditions.
According to the NHS and persistence of phantosmia can be a sign of Alzheimer’s, epilepsy, Parkinson's or a brain tumour.
Phantosmia is also known as an "olfactory hallucination" and the smell is unique to the person and is usually unpleasant, spoiling the taste of any food or drink consumed.
It can be in one or both nostrils, experts warn.
There are a wide range of possible causes of phantosmia, which include nasal infection, nasal polyps (abnormal tissue growths that form inside the nasal passages and sinuses), migraines, dental problems, smoking and exposure to certain chemicals.
Less commonly, the cause of phantosmia is either nerve cells sending abnormal smell signals to the brain, or a problem with the brain itself.
Some people with phantosmia will find that the smell gradually fades over a few months, and no treatment is needed.
If it is caused by an illness such as sinusitis, it should go when you recover from the illness.
Otherwise, if it persists, the following treatments may be tried:
You must always weigh up the benefits of these treatments with the possible side effects – speak to your doctor about this.