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Causes of smell and taste impairment
Home Causes of smell and taste impairment
Smell & Taste

Information on Smell Disorders

Smell loss is the most common type of olfactory disorder.

Anosmia is the medical term for the absence of the sense of smell, whilst hyposmia refers to a reduced sense of smell. The point at which hyposmia becomes anosmia and vice versa isn’t exactly clear, however, and there are many degrees of olfactory loss; some people lose it completely and suddenly whilst others experience it gradually over time, sometimes not realising that it is deteriorating. Some people are born without a sense of smell – this is known as congenital anosmia.

Anosmia is regarded as being a rare condition but is probably more common than many people think. Various studies have been undertaken in a number of countries to try to establish the prevalence of smell loss.  These have suggested that anywhere from 0.1% to over 5% of people have anosmia whilst up to 50% experience hyposmia. Results will of course vary according to who was surveyed in each study, but taking all this into account it is perhaps reasonable to say that potentially around 5% of the population has anosmia or severe hyposmia.

Qualitative Olfactory Disorders

These are usually side-effects of olfactory loss rather than conditions in their own right. Parosmia refers to distortions of the sense of smell, where an odour can be perceived but it doesn’t smell the way it should (and it is usually unpleasant). Phantosmia, as the name suggests, refers to ‘phantom’ smells; being able to detect an odour when there is no actual smell present.

Causes of Olfactory Disorders

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Sinonasal disorders and allergies These conditions are responsible for what clinicians call ‘conductive olfactory loss’; obstruction in the nose that prevent odourant molecules reaching the olfactory receptor neurones. The following conditions all fall within this category:

• Chronic Rhinosinusitis
• Deviated septum or foreign body obstructing the flow of air
• Allergic rhinitus caused by pollen, dust, animal hair etc
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Congenital anosmia Occasionally people are born with no working sense of smell. Why this happens is not well understood although sometimes this may be part of a condition called Kallmann syndrome, which includes a lack of hormone production in the pituitary gland due to a defect in the part of the brain called the hypothalamus. There are also people who may believe they have had no sense of smell from birth but have perhaps lost it at a young age due to a virus or a head injury, and therefore have no memory of having the ability to smell. 
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Post-viral olfactory loss (PVOL) It’s probably safe to say that everyone has lost their sense of smell for short periods during their life when they’ve had a cold or flu.

For some people, however, the symptoms of the cold clear but the sense of smell does not return. The various viruses that cause the common cold and flu can damage and interfere with the olfactory epithelium, the lining at top of the nose that contains the olfactory receptor cells.
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Idiopathic anosmia This refers to those for whom no cause for the loss of sense of smell is found, even after extensive testing. It is important that this diagnosis is made only after blood tests and brain scans have been performed. It can be really hard to never have a reason for a long term condition, it is important to talk with medical professionals to ensure all causes have been considered - see the section below about other possible causes that cannot be easily categorised.
Other causes

Other less common causes for smell loss include:

  1. Exposure to toxins
  2. Latrogenic (caused by medical treatment)
  3. Stroke
  4. Tumours
  5. Other medical complaints – diabetes, poor kidney function
  6. Parkinson’s Disease
  7. Alzheimer’s Disease
  8. Epilepsy
  9. Drug abuse
  10. Chronic alcoholism

Information on Taste Disorders

The Smell, Taste and Flavour page of our site explains how anosmia results in a marked reduction in the ability to detect flavour in food and drink, and how many patients who believe they have problems with their taste are, more often than not, suffering from a smell disorder.

However, there are instances when a person’s ability to taste food is compromised whilst their sense of smell is unaffected. For example, loss of the sense of taste (ageusia) means that the ability to detect the basic tastes, sweet, sour, bitter, salt and umami, is lost, but the sense of smell is unaffected. Taste-specific disorders are far less common than smell disorders, for example only 3% of the patients who have passed through Carl Philpott’s Smell and Taste Clinic at James Paget Hospital have suffered from a taste disorder.

Causes of Taste-specific Disorders

These are wide-ranging, and the list below is not exhaustive.  The most common cause of taste loss is ageing, as with smell loss.

– Medications – taste impairment is an unwanted side-effect of many medications, with some actually altering the way that flavour is perceived; numerous drugs, for example, including some used as part of treatment for cancer can cause a metallic taste in the mouth.  Others can interfere with saliva production, or disrupt the function of taste cells in the mouth.

– Damage caused by ear, nose, or throat surgery

– Chemotherapy for (typically) throat cancer

– Smoking

– Neurological disorders, i.e. strokes, epilepsy