Smelling something that is not present, perceiving a familiar smell differently or having a reduced sense of smell can have many causes. An unusual smell alone cannot diagnose a disease. MedlinePlus and the National Institute on Deafness and Other Communication Disorders (NIDCD) describe different types and causes of smell disorders, including respiratory infections, sinus conditions, injury and some medicines. NIDCD distinguishes parosmia, a distorted sense of smell, from phantosmia, smelling something when no odor source is present.
Types of changes in the sense of smell
Some people have a reduced sense of smell or cannot smell. Others notice that familiar odors seem different, or smell something when there is no actual source. These experiences have different medical names, but the cause cannot be identified just from the type of smell.
What to note and when to seek medical care
Note when the change started, whether it affects one or both sides, whether you have nasal congestion or recently became ill, and whether you started or changed a medicine. This information may help a clinician assess the situation. Do not stop a prescribed medicine on your own. If the loss of smell persists, worsens or occurs with other unexplained symptoms, arrange an assessment with a healthcare professional.
If you smell smoke or gas, first check the actual source and make sure the area is safe. Do not assume it is a symptom, because a change in smell may make it harder to notice a real household hazard.
Frequently asked question
Does an unusual smell mean that I have a serious disease?
Not necessarily. Smell changes have many possible causes and do not point to one disease on their own. If the change persists or worsens, seek an assessment rather than diagnosing yourself from an online symptom list.
References
About the source video: it is related to the topic of smell, but its transcript has not been checked against the audio. This article does not claim to diagnose anyone based on statements in the clip and uses MedlinePlus for information about symptoms and seeking care.