Anosmia is the total and often temporary loss of the sense of smell. Hyposmia is the partial loss of the sense of smell. Without the sense of smell, the sense of taste is also substantially diminished.
For our brain to detect a smell, specific chemicals found in food or any odorous substance must come into contact with olfactory cells in the upper part of the nostrils. The olfactory cells then send a signal to the brain. Any condition that interferes with the passage of smells through the nose can result in anosmia or hyposmia.
The most common causes of anosmia and hyposmia are viral infections (e.g. the common cold), allergies, sinus infections, poor air quality, nasal polyps, trauma, medications and certain diseases, such as Alzheimer’s, Parkinson’s and multiple sclerosis.
Anosmia and hyposmia are typical symptoms of COVID-19, occurring in more than 50% of infected individuals.