Ninety per cent of our sense of taste is down to what we smell London - Arabstoday Our ability to smell vastly improves our enjoyment of life — indeed, it’s thought that 90 per cent of our sense of taste is actually down to smell. Smell is also vital in alerting us to potential danger — such as smoke, for instance, a gas leak or spoiled food. Our sense of smell is triggered when microscopic particles released by substances such as perfume in the air or freshly ground coffee are breathed up throughthe nostrils, explains Henry Sharp, an ear, nose and throat surgeon at East Kent Hospitals. ‘The cells send an electric signal to an area at the bottom of the brain specifically concerned with smell, known as the olfactory bulb,’ he says. ‘Smell can also be triggered as we chew food, through the channel that connects the roof of the mouth to the nose.’ Sense of smell is often affected temporarily by a cold because the nasal passages become blocked with excess mucus, and the tissue that lines the nostrils becomes inflamed and swollen. However, in some cases a loss of smell can persist. Experts stress that most problems can be tackled if caught early. ‘If you experience problems for more than six weeks after a cold or flu, or suddenly become aware of problems,  it’s important to see your GP,’ says George Murty, a consultant ear, nose and throat specialist at the University Hospitals of Leicester. ‘They will take a history, check for any obvious blockages and, if necessary, refer you on to a specialist.’ Here, our experts detail some of the possible causes of both a temporary and permanent loss of smell:  Your sense of smell could be affected by too much cleaning. ‘Using strong household cleaners, such as bleach, a few times a week in unventilated areas such as a small bathroom can cause the toxic smell to affect the delicate lining and sensory cells in the nose,’ says Mr Murty. ‘This applies to the serial cleaners among us at home, but is also particularly relevant to those who work in industries that use chemicals such as chlorine, acids or solvents — or are even surrounded by metal dusts — on a day-to-day basis.’ Whether the sense of smell returns  depends on how long there’s  been a problem and how badly  the cells have been affected: it can be permanent.  Nerve damage — or neuropathy, the long-term complication of diabetes — is most commonly associated with pain and numbness or tingling in the hands, legs or feet. But this damage can also extend in some cases to the sensory nerves in the nose controlling smell. In a recent study at University Hospital Henri Mondor in France, all 68 diabetic patients scored significantly lower in recognising smells than the 30 healthy participants.  With the joy of changing nappies ahead of you, loss of smell during pregnancy may be no bad thing. ‘Affecting up to 30 per cent of women during pregnancy, smell loss — usually reduced rather than total — tends to occur during the second and third trimester,’ says Mr Murty. ‘This occurs because the higher amounts of oestrogen during this time lead to increased blood flow in the body (to accommodate for the growing foetus). ‘This then causes the tiny blood vessels in the nose lining to swell up, blocking the pathway of any particles going up the nose.'  Your heart function may improve with high-blood pressure medication but your sense of smell might not. Although rare, it is a documented side-effect for certain heart medications — including Enalapril — although it’s not clear why. Fortunately, arranging a change of medication with your GP will usually remedy problems rapidly.  Ignore a sore tooth at your peril; as well as being painful, it could affect your sense of smell. ‘Infection occurs when bacteria spreads inside the teeth or gums, causing a chronic dental infection or, in some cases, a dental abscess,’ says Dr Helen Stokes-Lampard, from the Royal College of General Practitioners. Bacteria can spread into maxillary sinuses, the small, air-filled spaces behind your cheekbones — and can cause inflammation, soreness, fever and a loss of smell.  Along with deteriorating sight and hearing, a reduced sense of smell is another sign of ageing. Up to 25 per cent of those over 60 may suffer from this — and this figure may increase to 62.5 per cent in those aged 80 to 97, according to a study carried out at San Diego State University and the University of California. ‘As we age, the number of fibres in the olfactory bulb starts to decrease, hence there’s less sensitivity to smells,’ says Jamie M. Boyce of the University Hospital of Wales in Cardiff, who has written a paper on the effects of ageing on smell and taste.  The production of red blood cells is probably vitamin B12’s most important role, but it plays a key role in our ability to smell, too. This is because it helps maintain the sheaths which surround and protect nerves, and are vital for transmitting electrical signals, including those from the roof of the nose to the olfactory part of the brain. ‘A deficiency occurs when the vitamin, which is found in foodstuffs such as dairy products, meat and eggs, fails to be absorbed through your small intestine,’ says Dr Anton Emmanuel, gastroenterologist at University College Hospital, London. The usual triggers are age and acid reflux medication.  Scientists have long been looking for ways to identify Parkinson’s at the earliest stages of the disease — the earlier it is treated, the better. Now studies are showing that a loss of smell can predate the  onset of clinical symptoms by several years. In one study carried out in Honolulu, researchers found that men with the lowest smell recognition scores were more  than five times more likely to develop Parkinson’s disease compared with those with the highest scores. A loss of smell is caused by the same disease process that leads to problems with movement, a better known symptom of Parkinson’s. Essentially, the disease leads to a reduction in the number of brain cells that produce dopamine, the chemical that controls communication between nerve cells. ‘Alzheimer’s is another degenerative neurological condition for which a loss of a sense of smell and ability to distinguish between smells is among the earliest symptoms — sometimes years earlier,’ says Dr Cockerell.  Sinusitis causes inflammation, which leads to a headache, temperature and a loss of smell, which is more significant than that experienced in a common cold. ‘If the inflammation of th sinus lining is long-standing and unchecked, nasal polyps may form, which look a bit like grapes hanging down from the sinuses inside the nose,’ says Mr Sharp. As these are thought to be caused by this chronic inflammation, treatment usually involves steroids or surgery. Generally, the patient’s sense of smell can be improved.  According to a study at Montreal University in Canada, anything from mild to severe traumatic brain injury — such as a sports injury or car accident — can cause a problem with smell. It’s also more likely to happen if the injury occurs to the front of the brain, which responds to smell messages. ‘It occurs because the force of impact shifts the brain within the skull, tearing the delicate nerve fibres that connect your nose to the brain,’ says Dr Oliver Cockerell, a neurologist at Barts and the London NHS Trust and the London Clinic. Unfortunately in these cases, there is no specific treatment, but in up to 39 per cent of patients the nerves can re-grow, and this can occur up to three yearsafter the injury,