What gives us our ability to smell? What can take that ability away? Is age a factor? What are the consequences? And what can we do if we start to lose our sense of smell? 

What gives us our sense of smell? 

Smells are detected in the nose by specialised receptor cells known as olfactory neurones. Extending from each olfactory neurone are 8-20 olfactory cilia, hair-like structures extending though the mucous. These contain the actual smell receptors. 

When an odour molecule (oderant) binds to cilia it sets off a signal that travels along the olfactory nerve to the olfactory bulb, underneath the front of the brain. The brain then interprets patterns in electrical activity as specific odors – i.e. something we can recognize as smell. 

What factors affect our sense of smell? 

Some of us may be born with a better sense of smell than others, just as some people may be born with better hearing, sight or sense of taste.

However, during our lives, many factors can then influence our sense of smell including: 

• The common cold, as well as zinc containing nasal sprays used to treat it
• Other respiratory infections, chronic rhinitis and sinusitis
• Smoking
• Certain medications such as common cholesterol lowering drugs and blood pressure drugs
• Nasal polyps
• Neurodegenerative diseases such as Parkinson's and Alzheimer's.  

Additionally a deviated septum - the membrane separating the two halves of the nasal passage - may cause difficulties with our ability to smell.  

Other factors can include hormonal disturbances, dental problems, exposure to chemicals such as insecticides and solvents, radiation for treating head or neck cancer, head or nose injury that damages the olfactory nerves and slow growing brain tumours that press on the olfactory nerves.  

Does our sense of smell deteriorate with age? 

Age may affect our ability to distinguish one smell from another. A reduction in our sense of smell is known as hyposmia, while a complete loss is called anosmia.  

This deterioration in our sense of smell affects more men than women and is most marked beyond the age of 70. It is thought to be the result of a reduced ability to keep up with the constant loss and replacement of the olfactory cells. Also the amount of mucous which is produced and which normally helps secure the cilia is reduced as we get older. Problems caused by a deviated septum may also become more acute during later life.  

How many older people are affected?  

Up to half the population between the ages of 65-80 may be affected. In those over 80 over 60% may experience a reduction in sense of smell. Of the original 10 million or so olfactory cells normally found in the nose as many as 60% of these may be lost with age.

Furthermore as people age they may even lose their ability to taste food and drink. Where this coincides with a loss in the sense of smell this can make it difficult to enjoy food and drink and may therefore result in loss of appetite. 

The consequences when our sense of smell deteriorates 

 Smell is often our first response to stimuli.  

• It can alert us to fire before we see flames.
• It makes us recoil before we taste rotten food.
• It provides us with an ability to detect and avoid many poisonous or dangerous gases. 
• It also makes us aware of our own personal hygiene.  

The loss of our sense of smell affects enjoyment and interest in food since taste and smell are so intimately entwined. As a result older people may show less interest in food, which can lead to a significant reduction in appetite and potential dietary deficiencies.  

Also loss of sense of smell may have a profound effect on our quality of life, leaving us unable to smell new mown grass, autumn leaves or highly scented flowers. Gone too may be the ability to recapture nostalgic memories previously readily recalled by the scent of a particular perfume.  

Can loss of sense of smell predict serious diseases?  

Research suggests that losing our sense of smell can be a possible predictor of health risks - including a higher risk of Alzheimer's and a higher risk of dementia  in general, according to studies published in 2017 and 2018. Several studies also suggest that losing our sense of smell may indicate a higher risk of early mortality, like a study of 1,774 adults over a 10 year period in Sweden, published in 2017. 

However, as mentioned earlier, many factors influence our sense of smell, so we shouldn't assume that losing our sense of smell will automatically lead to health risks.

Diagnosis  

If loss of sense of smell is a problem it is important to obtain a proper diagnosis from an ENT (Ear, Nose and Throat) or allergy specialist. Depending on the cause they may be able to prescribe appropriate treatment. 

What else can you do if you’re losing your sense of smell?  

Suggestions here include: 

• Avoid known triggers, like smoking and contact with allergens that cause rhinitis (like cat allergies or whatever you are susceptible to).
• Consider suitable adaptations. For example switch to an electric cooker in place of gas, install smoke alarms, check and adhere to "use by dates" on food packaging.
• For personal hygiene a regular routine for personal washing and bathing, change of clothing etc. may be more appropriate than relying on your sense of smell.
• To restore your enjoyment of food consider additional seasoning particularly that which is sharp and acidic such as lemon juice and more liberal use of spices.  

Can we improve our sense of smell?

It seems that training our sense of smell may help restore it, particularly where this has been lost following a severe respiratory viral infection. A review of ten studies, published in 2016, concluded, 'it may be an effective treatment for olfactory dysfunction due to multiple etiologies.' While an analysis of 13 studies, published in 2017, concluded, 'our meta-analysis showed that such training should be considered an addition or alternative to existing smell treatment methods'. The training involves repeatedly smelling four to six distinctly different odours such as cloves, roses, lemon and eucalyptus each day over a period of several weeks. Success is dependent on the duration of training and the number of different odours used  

Conclusions 

• Age is one of a range of factors that can reduce our sense of smell.
• Losing our sense of smell removes one of the ways our bodies can identify risk – and reduces our enjoyment of food and of life.
• It may even be an indicator of future illness.
• So it is important to see your doctor if you start to lose your sense of smell.
• Training our sense of smell may help restore it.
• If this isn’t treatable then consider suitable adaptations (like an electric cooker rather than gas).  

To return to Ageing and senses click here.

Reviewed and updated by Richard Franklin February 2018. Next review date January 2022.