Introduction

Our sense of smell (olfaction) is one of the oldest of our senses from an evolutionary perspective and has more nerve connections than either vision or hearing. Although it is much less sensitive than that of animals, our sense of smell is still vital. It keeps us safe by guiding us when food has spoiled or warning us when there is a fire or a gas leak. It also, gives us emotional pleasure through smelling flowers, perfumes and fresh foods. Additionally, our smell nerves connect with many areas of the brain which is perhaps why smelling some fragrances or scents can be associated with past memories.

Consequently, when people lose their sense of smell, this can have a potentially significant impact upon their lives.

How common are smell issues?

We define a complete loss of smell as anosmia and a partial loss as hyposmia. This is a surprisingly common issue with about 1 in 5 people having issues with smell loss between the ages of 20-50 to as high as 8 out of 10 people who are above 80 years old. However, it is not often noticed until others point out a smell that is not picked up by an individual with smell loss. That said, as our sense of smell greatly contributes to the flavour of foods, those with smell loss find that foods can taste more bland and in fact most causes of loss of taste are a consequence of a loss of ability to smell.

Smell disturbance can also cause some people to sense bad smells (cacosmia), altered smells (parosmia), sensing smells in the absence of any odors (phantosmia) or inability to classify what a smell is (olfactory agnosia).

How do we smell?

The main function of the nose is to condition the air that we breathe and this is related to the structure of nose. However, within a small area in the roof of the nasal passageways, the lining of the nose contains specialised nerve endings that detect smells that join other nerve endings in a region called the olfactory bulb.

There are about 100 million of these nerves which then connect to pathways in our brain. In comparison with other nerves in the human body, they are unique as they are the only nerves that can regenerate and they do so every 30-60 days.

When we breathe in and more so when we sniff in, odor molecules contained with the air reach the area of the smell nerve endings (receptors). They then pass through the mucous that covers the nasal lining and are sensed by the smell receptors. Interestingly, as well as air passing through the nostrils, little puffs of air pass through the back of the nose when we are eating which combines with our sense of taste and provides us with the experience of flavour for foods.

What causes smell disorders?

Smell disorders are either caused by smell molecules not being able to reach the smell receptors (conductive or transport issues) or due an issue with the receptors and the nerve pathway to the brain. Within the latter group, this can be due to ageing in a similar manner to hearing loss that occurs as we grow older, infections affecting the nerves and head injuries which disrupt the delicate nerve fibres and their connections.  Less commonly, nerve disturbance can be due to changes in our body’s hormones, as a side-effect of some medicines, related to some disease affecting the nervous system and rarely due to genetic issues.

Within the conductive group of causes, this can be due to nasal blockage because of:

Sinus disease

Sinus disease with nasal polyps

Inflammation of the nasal lining such as that due to allergies

Deviation of the nasal septum

Tumours within the nose

How is smell disturbance investigated?

In your consultation with Dr. Michael, you will be asked questions relating to your smell disturbance and general health. You will be asked to complete questionnaires and will have your nasal passageways examined with a fine, specialised camera called an endoscope. Your sense of smell will be assessed with validated smell testing kits and you may be asked to undergo blood tests and specialised imaging looking at the region of the smell nerves.

What can be done to help with smell disturbance?

We are still learning about the mechanisms and management of our sense of smell and smell disturbance. However, early recognition and treatment is thought to have the most favourable prognosis to aid with smell recovery. The modality of the management of your smell disturbance will depend upon your symptoms and findings during your examination. With causes which are suspected to be due to a conductive element i.e. blockages preventing the smell molecules reaching the smell nerve endings, surgery to clear blockage may be an option. This may be in the form of a septoplasty, turbinoplasty or sinus surgery.

If it is thought that the issues lies more with the nerve endings and their pathways, then non-surgical options will be considered dependent upon the exact cause that is suspected.

What is the chance of smell returning?

The treatments for returning the sense of smell unfortunately as yet are not guaranteed. However, smell disturbance due to conductive issues has a more likely chance of being improved rather than those that occur due to issues with the smell nerve endings and their pathways.