Forgotten Sense of Smell

Olfactory dysfunction is often ignored or trivialised; but it reduces quality of life and can be a debilitating condition. Losing the sense of smell permanently may lead to social isolation, depression and suicide.

Smell loss can be quantitative and qualitative – with distortion in perception. Partial smell loss is called hyposmia; whereas total smell loss is termed anosmia. Distorted smell is abnormal perception of normal smells – parosmia – or the detection of imaginary smells that don’t really exist – phantosmia.

Smell disorder has a prevalence of  about 4-25%, and is more common with age. Men are more likely to experience problems with smelling, especially if they work in a factory and are of low education and low income. Between 10 and 60% of those with smell disorder also have distorted smell perceptions, which are more common when smell loss is only mild.

Causes of Olfactory Dysfunction

The three main causes of smell disorders are sino-nasal disease, upper respiratory tract infections and head trauma.

Sino-nasal disease – caused by chronic inflammation due to infection or allergy of the nasal passages – is the most common. Polyps or inflammation may block the nasal passages or para-nasal sinuses – eg rhinitis or sinusitis  both. Olfactory symptoms occur in more than half of those with chronic nasal or sinus inflammation.

Upper respiratory tract infections can cause permanent damage and smell loss can continue long after infection has cleared and symptoms are gone. Patients with post-viral olfactory loss often retain some smell capacity and smell distortion is very common in these patients. Head trauma can cause very severe olfactory loss with sudden onset.

Some meds may distort smell temporarily. Drugs used in anaesthesia can impact on olfactory function, so eican be impaired after surgery. Some drugs or toxic chemicals in the environment also damage the sense of smell.

About 3% inherit their smell disorder. Rare olfactory perception disorders are linked to neurology conditions, for example, in epilepsy, migraine, Parkinson’s disease, or schizophrenia.

In some cases, there is a sudden recovery of all or part of their sense of smell. This is more likely in younger patients, and in those whose dysfunction was due to a viral infection. The sense of smell can return even after many years, but it is less likely to occur the longer it has been present.

Treating Olfactory Dysfunction

No specific treatment is in widespread use despite the burden of smell loss and the impaired quality of life. Patients who are treated successfully have a much higher satisfaction with their life.

Dysfunction can fluctuate and can be modulated by physical exercise and hot showers. Treating the underlying sino-nasal disease is likely to improve sense of smell. Antihistamines may help. Nasal or systemic corticosteroids and surgery may be of benefit.

Peroral caroverine, an N-methyl-D-aspartic acid (NMDA) receptor antagonist, as well as sodium citrate nasal spray have been shown to be effective in proper trials. In addition to drug treatments, acupuncture and olfactory training have also been investigated with some reported success.

Many other proposed treatments have proven not to be of benefit or require proper validation. Zinc, vitamin A and the antibiotic minocycline have all been shown to lack good evidence as to their effectiveness. α-lipoic acid and the phosphodiesterase inhibitors theophylline and pentoxifylline need to be investigated further.

It is likely that any successful treatment of smell loss also improves associated symptoms of distorted olfactory perception. However, some treatments, like the surgical excision of olfactory sensory neurons, bilateral olfactory nerve sections, and repetitive TMS specifically target smell distortions.

Social Problems

We use our sense of smell for many social functions. Olfactory impairment is not considered to be a serious disability and empathy can often be lacking. Sometimes affected individuals with smell lose are even told that they should be happy about their inability to smell unpleasant odors.

The enjoyment of eating and food is an obvious role for olfaction. Many of those who lose their sense of smell don’t enjoy eating much and they can either gain or lose weight. They may shift their food preferences significantly after onset.

If you can’t smell then you lose your ability to detect bad or noxious smells, cleanliness and body odours. This can lead to social insecurities about how the sufferer is perceived by others or smells in public places. It can lead to frustrations and there may be lack of sympathy or intolerance of the problems this causes.

Loss of smell causes a reduced ability to enjoy and experience pleasure of pleasant smells. It can lead to a loss of motivation to engage in pleasurable activity or anhedonia. This can trigger mood changes and the onset of depression.

Distorted olfactory perception is even more detrimental to the quality of life than smell loss.Phantosmia, in particular, has an associated increased risk of suicide.

One important function of smell is contributing to the experience of places and memory. Even though we are not always aware of the smells in different locations, these smells often determine our experience and enjoyment of occasions.

Distorted Olfaction

Phantom smells can be particularly disturbing as they can be bad odours that are perceived. However, not all distorted odor perception is unpleasant.

In the most common situation, the same smell is perceived no matter the trigger, but there can be different phantom smells with different triggers. Describing odors and identifying them out of their usual context is notoriously difficult. This can make it difficult to communicate what the problem is and can lead to frustrations and fears of being considered ‘crazy’ by others. Olfactory hallucinations can come with the stigma of experiencing things that do not exist, so many don’t report their experiences to others.

The regular smelling of an unpleasant odour can affect mood and emotions. It makes daily life complicated and going out in public can be embarrassing and traumatic. Eating in particular becomes a difficult chore if the food smells bad.

Having a smell disorder is disabling and can significantly impact quality of life. Although sufferers do suffer severe consequences and often social stigma, their condition can be ignored or trivialised.


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