Anosmia (loss of sense of smell)

Anosmia is the medical term for loss of the sense of smell. It's usually caused by a nasal condition or brain injury, but some people are born without a sense of smell (congenital anosmia).

Losing your sense of smell can be very depressing and isolating. It means missing out on many experiences most of us take for granted, such as smelling fresh flowers, perfume or the scent of a loved one.

Smell also plays an important role in how you taste things. Many people with anosmia lose interest in food, because 80% of the flavour of food comes from its smell.

If you've suddenly lost your sense of smell and don't know why, see your GP. They may be able to diagnose an underlying cause (see below) and offer treatment to restore your sense of smell.

Seeing your GP

Your GP will want to take your full medical history, examine the inside of your nose and take a blood sample for testing in a laboratory.

Your doctor may refer you to an ear, nose and throat (ENT) specialist in hospital. Further tests, such as a CT scan, MRI scan or nasal endoscopy (where a thin tube with a camera is inserted up your nose), can be used to investigate the cause.

What are the causes?

There are several medical conditions and medications associated with a loss of smell. The possible causes include:

• a viral infection affecting the upper respiratory tract, such as a cold
• persistent (chronic) sinusitis, with or without nasal polyps
• a nose abnormality, such as a crooked nose or a nasal septum (wall dividing the nostrils) that isn't straight
• hay fever (rhinitis) that causes severe inflammation of the nasal passages
• certain medication, including antibiotics such as metronidazole
• recreational drug use such as cocaine or amphetamines
• diabetes
• long-term alcohol misuse
• an underactive thyroid
• Cushing's syndrome (high levels of the hormone cortisol in the blood)
• exposure to a chemical that burns the inside of the nose
• a head injury
• a brain tumour
• radiotherapy to the head and neck
• epilepsy
• Parkinson's disease
• Alzheimer's disease
• stroke
• liver or kidney disease
• vitamin B12 deficiency
• schizophrenia
• granulomatosis with polyangiitis – an uncommon disorder of the blood vessels
• sarcoidosis – a rare disease that causes body cells to form into clumps

In general, anosmia is usually caused by either a problem with odours getting to the top of the nose (because of swelling or a blockage in the nose) or a problem with nerve signals from the nose to the brain.

However, in around 20% of cases, the cause can't be found. This is known as idiopathic anosmia.

Congenital anosmia

An estimated 6,000 people in the UK are born without a sense of smell because of a genetic condition or faulty gene. This is known as congenital anosmia.

It can occur alone (isolated congenital anosmia) or it can be a symptom of another genetic condition, such as Kallmann syndrome or Klinefelter syndrome.

Can anosmia be cured?

Whether or not anosmia can be cured depends on the underlying cause.

People with congenital anosmia have a lifelong inability to smell and have no concept of what a smell even is. Currently, there's no known cure or treatment for congenital anosmia.

However, other types of anosmia may be improved or cured when the underlying condition is treated. For example, if the cause is swelling in the nose or sinuses, steroids can usually clear this up and restore your sense of smell.

Treatments that may help, depending on your condition, are:

• nasal washing (douching)
• a steroid nasal spray
• an antihistamine
• steroid tablets
• an operation to have nasal polyps removed
• an operation to straighten the nasal septum
• an operation to clear out the sinuses, called endoscopic sinus surgery (ESS) (see below)

These treatments may come with unpleasant side effects. Speak to your doctor about whether any of these treatments may be suitable for you and, if so, what side effects you may experience.

ESS

In bilateral endoscopic sinus surgery (ESS), the surgeon opens all your sinuses and clears them out to reduce inflammation and allow nasal rinses and sprays to reach them. In some centres, this may involve the use of an image guidance system (IGS) to map out your sinuses. ESS also involves removing any polyps present at the same time.

This treatment can bring back some sense of smell for many people with anosmia when medication alone has failed. However, if you don't keep taking your nasal medications afterwards, the anosmia is likely to return.

If you've had surgery to remove nasal polyps, it's quite common for these to grow back, and many people find they need another operation. However, ESS may reduce the need for further surgery.

A recent journal publication looked at how successful ESS with IGS was in treating patients with chronic frontal sinusitis, some of whom also had nasal polyps. Data from a five-year period showed that only four patients out of 141 (3%) needed to have further surgery after having ESS with IGS as their first operation. IGS is not available in all hospitals, but may be performed by specialist centres where possible.

Safety

If you have anosmia, you'll need to take special precautions because you won't be able to smell fires, poisonous fumes, leaking gas or food that has gone off.

It's recommended that you:

• install smoke alarms in all areas of the home, especially in the kitchen and near the fireplace
• change from natural gas appliances to electric or consider installing a natural gas detector
• clearly mark expiry dates on food and mark leftovers with dates, so you know when to throw them away
• carefully read warning labels on products such as bathroom and kitchen cleaners, and insecticides, to be aware of potent chemicals

Some people with anosmia also experience a loss of appetite, but it's important to maintain your nutrition levels. It may help to set reminders for mealtimes and weigh yourself regularly to ensure you stay healthy.