Anosmia

Anosmia is the full loss of the sense of smell. Partial loss of the sense of smell is known as hyposmia. Both conditions can be temporary or permanent. Anosmia and hyposmia are smell disorders. Other conditions in this category include parosmia, which causes changes in normal odour perception, and phantosmia, which causes the perception of odours that aren't there.

Loss of smell can have a significant impact on a person's quality of life, since smell allows us to enjoy pleasant aromas, such as the smell of food. Anosmia may also be accompanied by a loss of taste. Our sense of smell also acts as an alarm system, alerting us to dangers such as a gas leak, rotten food, or a fire. Since they cannot smell potential hazards, people with anosmia are advised to make sure their smoke detectors are in good working order.

Causes and triggers

Normally, smells reach the brain by way of olfactory neurons in the nose. Sometimes, smells are unable to reach these neurons due to blockages or inflammation (e.g., polyps, a stuffy nose). In other cases, a person may have fewer olfactory neurons.

Anosmia can be caused or worsened by a variety of factors. These include:

• A head injury (e.g., car accident, surgery)
• A viral infection (e.g., influenza, COVID-19)
• Aging
• Diseases that affect the nervous system (e.g., Alzheimer's disease, Parkinson's disease, stroke)
• Diseases that affect the sinuses (e.g., sinusitis, nasal polyps, allergic rhinitis)
• Exposure to certain chemicals, toxins, metals, medications, and drugs
• Smoking
• Certain endocrine diseases (e.g., hypothyroidism, diabetes)

Treatment

Treatment for anosmia varies, depending on the cause. If it is caused by a blockage in the nose, as in the case of sinusitis or allergic rhinitis, medication may be used to treat the source of the problem. For nasal polyps, tumours, or deformities, surgery may be required.

If the cause of anosmia lies in how the brain interprets smells, olfactory (smell) retraining may help. This involves stimulating olfactory neurons with various scents to help revive the sense of smell.

When should I see a health care professional?

Speak with your health care provider if you notice a partial or full loss of smell or any other olfactory issue. An investigation will be done to determine the cause.