Making sense of smell
loss after brain injury

"Like living behind a pane of glass"

Up to three and a half million people in the UK could be experiencing smell loss, with head injury among the top four causes. But often it goes untreated for years, despite having a profound impact on a person’s quality of life. Sarah Sinclair reports on a webinar on the topic. 

Duncan Boak can’t tell when the milk has gone off. Nor can he remember the smell of fresh basil, even though he chops it every time he cooks a tomato sauce. 

After suffering a head injury in 2005, Duncan lost his sense of smell. “I was in hospital for a week after the accident, eating very little. It was when I came out of the hospital and had the first meal since the accident at my parent’s house when I realised I couldn’t smell anything,” he says.

“I went to see my doctor and was told nothing can be done, he said to give it time, that it might come back on its own accord and if it doesn’t ‘you will just have to live with it’.”

At the time Duncan felt that he had gotten off lightly, but in the months after the accident he began to experience depression. 

Without his sense of smell he lost his appetite and, as a result, a lot of weight. “I’m a pretty slim guy anyway, but I was a bag of bones for a while,” he says.

“The thing with loss of smell is that there is a lasting, ongoing loss of quality of life. We’re not just talking about the eating experience, it’s the removal of a really important emotional connection to the world around us and to people in it.

“There is an ongoing feeling of disconnection, of being removed from the world. It can be a bit like watching life from behind a pane of glass.”

In 2012, Duncan founded Fifth Sense, the charity for people with smell and taste disorders.

A survey of its members published in 2014 as the Impact of Olfactory Disorders in the UK, found 92 per cent of respondents had found their enjoyment of food and drink had been reduced since losing their sense of smell.

In addition, 54 per cent had had relationship difficulties and 43 per cent experienced depression.

“It has a huge range of impacts, not only on the eating experience, but much more widely,” continues Duncan.

“You lose memories of smells and tastes, but some of the other dangers and difficulties include loss of confidence in your own abilities and there's the safety aspect - the fact you can’t smell gas or burning, or if food has gone off.

“If I’m worried about the milk I have to rely on my flatmate to smell it for me, but the safety aspects can be a greater concern for people who live alone." 

Making sense of it 

Research has shown that at least one per cent of people in the UK lack the ability to smell, with potentially five per cent (up to 3.5 million) reporting an impaired ability to smell.

But some studies suggest that experiences of smell loss could affect up to a quarter of the population.

There are various ways in which smell disorders can present: anosmia, where a person has no sense of smell; hyposmia, a reduced sense of smell; phantosmia, smelling smells that aren’t there and parosmia, having a distorted sense of smell, sometimes described as a smell of burning rubber or a pungent chemical smell or raw sewage.

According to Professor Carl Philpott, director of research and medical affairs for Fifth Sense, and Professor of rhinology and olfactology at the University of East Anglia, smell loss is as prevalent as sight loss and hearing loss in the UK, but often goes unreported.

“If it affects about five per cent of the population, that is more than sight loss in the UK [three per cent], and also profound hearing loss [one per cent], yet as things stand we don’t have a Royal National Institute to consider and account for patients with these disorders,” he says.

Head injury is among the top four causes of smell loss, along with chronic sinusitis and respiratory tract infections such as common colds, the influenza virus and, more recently of course, the coronavirus. 

But it can also be caused by comorbidities or long-term conditions such as Parkinson’s Disease or cancer.

“For those of us that run specialist clinics, head injury is a much more common presentation and post-traumatic olfactory loss (PTOL) is one of the most common reasons for people to present at my smell and taste clinic,” Prof. Philpott continues.

“It is thought that about one in three motor vehicle accidents involve the head neck region, and therefore it’s not surprising that loss of smell may accompany that.

“The other key thing is whether there’s any associated facial injuries, such as after an assault that results in a blockage to the nose.

“It can also be caused by a bruising of the brain - what we call a contra-coup injury or due to shearing of the fine olfactory nerve fibres as they cross the skull base from the nose into the brain.

“Occasionally, it could be that an individual patient already has a pre-existing problem with their nose and sinuses and the head injury exacerbates that underlying disorder.

“In cases where the TBI is thought to be a grade one, then the chance of olfactory dysfunction is around 18 per cent, but in cases where the injury is grades two and three, this goes up to 57 per cent.

“We think in head injury clinics around 10 percent of patients are reporting smell loss and probably not really getting much further action from there,” he adds, but believes this is an underestimate, with several reasons why patients might not speak up about smell loss.

For those who have suffered an accident, they may spend a long period of time in intensive care and are therefore not in a position to be aware, or may be dealing with much more severe injuries, and so a loss of smell is not a priority. 

Those who are conscious but in hospital may assume that the lack of ability to smell is down to the poor quality of hospital food. However, early recognition is key for treatment, with any recovery most likely to occur within two years after the head injury.

“Smell training is really a very simple but key thing that patients can do,” says Prof. Philpott. 

“Those who benefit tend to be younger, have a shorter duration of the disorder and less severe trauma, so getting people to see a specialist sooner rather than later is always beneficial.” 

He continues: “We can see partial recovery in about one in three people after head injury related smell loss, but complete recovery probably only occurs in about 10 to 15 per cent of cases. 

“The greatest chance of improvement is in that first period between up to 12 months. There is a potential for improvement after that period, but it becomes much lower.”

Last year, Fifth Sense developed SmellAbility – a toolkit to enable people to build their own smell training resources and provide physiotherapy for the nose.

SmellAbility provides information about the science behind smell training, tests to establish baseline ability, record sheets to measure how this changes over time and a diary log to record training, all of which can be downloaded or printed for use.

“It is important that people create their own smell training resources whether it is following the science and using essential oils, or using everyday items they have at home.

"We encourage people to choose a range of smells that they are familiar with so that they will recognise any changes or improvements,” says Nina Bleasdale, director of development and operations.

She goes on “we encourage people to use their other senses to support them. Take a real orange, grate the skin (which actually releases the natural oil used in creating essential oil), use your sight to enjoy how the orange looks, touch it to stimulate its full appeal and use your memory of what an orange smelled like to you – all of which can help to get the most from smell training”.