Changes in sense of smell are most often caused by:
These can cause:
It's also common to lose some of your sense of smell as you get older.
Rinsing the inside of your nose with a salt water solution may help if your sense of smell is affected by an infection or allergy.
You can make a salt water solution at home.
Some pharmacies sell sachets you can use to make a salt water solution and devices to help you rinse your nose.
They'll check for any obvious causes, such as sinusitis or nasal polyps.
They may refer you to a specialist for tests if they're not sure what the problem is.
Your sense of smell may go back to normal in a few weeks or months.
Treating the cause might help. For example, steroid nasal sprays or drops might help if you have sinusitis or nasal polyps.
A treatment called smell training can also help some people. The organisation Fifth Sense has more about how to do smell training.
Sometimes changes in sense of smell can't be treated and may be permanent.
If you have lost your sense of smell, you may not be able to smell things like gas leaks, fires and food that's gone off.
Fifth Sense has some safety advice if you have anosmia.