Allergic disorders appear to have reached monumental proportions. We may consider ourselves to be in control of our environment, but our bodies appear to be growing increasingly intolerant of it. One third of us in the developed world will develop an allergy to something at some point in our lives, according to experts. It is a miserable - and sometimes alarming - prospect. For some, allergies are seasonal and relatively mild.For others, the allergy is to a known food, such as cow's milk, and as long as we avoid the food, we will experience no problems. But for legions of people, allergies are so severe it affects their quality of life. Occasionally, the allergy is life-threatening, as in the case of allergic shock, or anaphylaxis, where blood pressure falls, the throat and mouth swell, and it becomes impossible to draw breath.
In the US alone, about 11 million Americans suffer from some degree of food allergy. Those with severe reactions may experience anaphylactic shock. Annually, around 30,000 people receive life-saving emergency treatment and 150 fatalities occur. The number of new cases in developed countries seems to be increasing rapidly. So why are allergies on the rise, and could we be partly to blame? The term "allergy" was coined by Clemens von Pirquet in 1906 to describe an unusual reaction of the immune system. Today, most doctors use it to describe hypersensitivity to something inhaled, swallowed, injected, or that simply touches the body.
Since the late 1950s, experts have noticed allergies rising, but only in the developed world. No such increases have been seen in developing countries. To confuse the issue, allergic diseases have also been changing. The most common allergic reaction is rhinitis, seasonal or year-round hay fever. However, an increasing number of people now suffer from food allergy and atopic eczema, a dry and itchy inflammation of the skin. And new allergies have emerged, such as latex allergy, suffered by around 10 per cent of doctors and nurses who have to wear latex gloves. Certain allergic conditions are severe or potentially life-threatening, for example, peanut allergy in young children is now increasingly common.
But a recent report from the UK Parliament suggested that well-meaning health advice had contributed to this problem. The report said that advice to pregnant women, for example, to avoid eating peanuts, and not to feed them to their children until they were at least three years old, could actually be responsible for a dramatic increase in peanut allergy. It cited the English island, the Isle of Wight, where peanut "sensitisation" had "increased three-fold" in children born between 1994 and 1996, when the advice was disseminated, compared to those born in 1989." Experts said exposing a child's immune system to peanut allergen at an early age could actually result in tolerance. In Israel, where the incidence of peanut allergy is lower than in the UK, peanuts are commonly used in infants' weaning foods. The matter is now being researched by Prof Gideon Lack, head of paediatric allergy at London's Imperial College.
Then there is the question of whether our obsession with hygiene has exacerbated the issue. An epidemiologist writing in the British Medical Journal suggested that one cause of the rise in allergies might be due to declining family sizes and higher standards of cleanliness. These two things provide young children with less exposure to germs and this is thought to give children's still-developing immune systems less practice in fighting off intruders. The result, the theory goes, is that the under-challenged immune system wants to be used, so it becomes primed to see harmless substances like dust and pollen as dangerous invaders, leading to allergies and asthma.
There may well be some truth to this idea, which has come to be known in medical circles as "the hygiene hypothesis". In 1997, a study of almost 12,000 families in England and Scotland found that the more children a family had, the less the incidence of asthma. A baby's immune system begins preparing for a germ onslaught before birth, with the placenta acting as a filter that lets through small amounts of innocuous allergens and microbes. Babies, it seems, are born ready to have their immune systems challenged.
So the message seems to be not to worry too much about the various bugs your baby may be encountering at nursery, from siblings or from the family pet. They may be the best thing for him or her in the long run. That's no consolation, of course, for those older children and adults suffering allergies now. But rigorous research means there is a much greater understanding of the complex nature of allergic reactions, which has led to more effective treatments.
For example, some experts say the allergy increase could be tackled with immunotherapy, a controversial treatment largely abandoned in the 1980s when it led to the death of a number of patients. The treatment involves injections of an allergen, such as wasp venom or pollen, to build up immunity, and it is now being regarded as the most promising way forward for many sufferers. Many doctors insist that the treatment is safe if administered in hospitals by specialists, with emergency equipment standing by in case of a severe reaction. There is evidence that it is highly effective for asthma. Unlike inhalers and nasal sprays, it may give long-term remission to sufferers.
Dr Colin Macdougall, the honorary consultant paediatrician at Coventry and Warwickshire University Hospitals Trust in the UK, says: "In terms of getting anywhere, it would seem that immunotherapy is the most likely route forward."It's been far from trouble free, but it has to be said that if we could mimic a similar process for food allergy, which is what I specialise in, it would probably have the most mileage for the future.
"At the moment, the only truly effective strategy for food allergies is complete avoidance, but you also need an emergency strategy in the form of antihistamines and adrenalin shots. "Immunotherapy is immensely useful because it is at the core of what we are trying to do which is to make someone non-allergic. None of the other approaches do this. "And in terms of hay fever it has been safe for a long time. However as far as I am aware, I don't know of anyone doing something with food that is anywhere near clinical use."
In Europe there is a study looking at children with rhinitis, which causes sneezing, treated by immunotherapy and now, after 10 years, they are 2.5 times less likely to have asthma than a group of children of a similar age treated with drugs. The progression from rhinitis to asthma can be almost completely halted by immunotherapy. So maybe we can regain some control over our allergies after all.