"Smell impacts on our lives in so many ways," says Duncan Boak.
"Emotions, memories, mood - they are all linked to our sense of smell."
Unfortunately for Mr Boak, 31, from London, his ability to smell is just a memory after a serious head injury nearly 10 years ago. But the experience has led him to set up the first charity in the UK providing support and advice to sufferers of smell and taste-related disorders.
Mr Boak's accident robbed him of all olfactory perceptions and meant, for a long time, that everything from eating food and walks in the countryside to personal relationships were no longer enjoyable.
"If you imagine every pleasurable activity you do, and then remove the smell from it. All pleasure and emotion disappears too.
"For me, nothing was ever the same again."
He particularly misses the aromas of Christmas and the rich scent of real Christmas trees, mulled wine, cold, crisp mornings and smoky fires.
Abi Millard, from Dorset, is nine years old and has never been able to smell. Her parents only realised she had a problem when she was about four because she never reacted or commented on bad smells, despite living in the country. She had always been a poor eater too.
Abi's congenital condition is rare and she has only recently been referred to a specialist clinic for treatment, after a series of doctors were left baffled by her problem.
She is looking forward to being seen by an expert who understands her disorder, because there are things she would love to smell.
"I'd quite like to smell cake and, this is a bit weird, but I'd like to smell yucky things like tractors too," she says.
It is thought that up to 5% of the UK population - 3.25 million people - suffer from loss of sense of smell or some form of impairment.
Anosmia, complete loss of smell, can be present from birth but is more likely to be caused by viral infections, nasal polyps and other sinus diseases. It can also occur when the frontal lobes of the brain are damaged, after serious head trauma, for example.
This area of the brain is where the olfactory nerve and olfactory bulbs, which control smell perception, are situated.
A sudden loss of sense of smell, which usually results in a degree of loss of taste, can have an enormous impact on people's lives - something not widely recognised or understood.
According to a survey of more than 400 people with smell and taste disorders by Mr Boak's charity, Fifth Sense, feelings of isolation, depression and anger are not uncommon.
The majority said their enjoyment of food and drink had been dramatically reduced and they were afraid of being exposed to dangers such as gas or mouldy food.
More than half also reported experiencing difficulties in their relationships with partners, families and friends.
Mr Boak suggests this is because "sense of smell is fundamental to the way we connect with each other".
The smell of hair, skin and clothes is an important element in intimacy with another person, while the smell of a newborn baby is a undeniably powerful bonding tool.
One of the main aims of Fifth Sense is educating the public about the vital role that sense of smell plays in their lives.
It was something Mr Boak had never considered before his own accident and it was only reading about someone else's experiences that prompted him to find out more about how smell and taste actually work.
It proved to be a turning point in his life. He has since learned to use other senses, including texture, to appreciate food and wine once more.
Appreciating the flavour of food is about combining the senses of taste and smell, he says, which he can no longer do. In fact, 80% of food flavour is down to smell.
But he can still tell the difference between sweet and sour food, between dry and sweet wines, and different coffees.
"If you can tell the difference between wines, you can have a preference for one or the other. And that can bring the enjoyment back."
It is also possible to retrain the brain to recognise some smell signals, through "smell training".
Carl Philpott, honorary consultant ear, nose and throat surgeon at the UK's only smell and taste clinic - at the James Paget Hospital in Gorleston, Norfolk - has treated many patients with smell and taste disorders.
He says medication or surgery can solve some disorders, but if that is not possible it is important to keep working at the process of smelling because improvements have been seen over the long term.
"The idea is that people think of smells they are familiar with and, by encouraging activity in the smell pathways, they can get flashbacks of smells.
"It's a simple measure but it gives people a sense of focus."
Without that focus, Mr Philpott finds that his patients are prone to psychological problems because their loss is invisible and they do not feel anyone understands their problems.
"Imagine, three times a day, spending your time chewing cardboard. That's what it's like for someone with anosmia to eat.
"We take sense of smell for granted, but suddenly it can go."