The Big Question: Why are allergies on the rise - and how can medicine combat them?

Why are we asking this now?

Britain is in the grip of an epidemic of allergic disease, according to the influential House of Lords Science and Technology Committee. The numbers affected have trebled in the last 20 years and a third of the population – 18 million people – will develop an allergy ranging from the trivial to the life-threatening, it said in a report yesterday. The UK incidence is among the highest in the world but Britain is lagging behind the rest of Europe in tackling the problem.

How big is the problem?

Very big. Taking asthma as an example, the growth of the asthma epidemic started in the 1950s and the numbers affected approximately doubled every 14 years until the mid-1990s. In 2004, research showed that 39 per cent of children and 30 per cent of adults had been diagnosed with one or more of asthma, hay fever and eczema.

Hospital admissions as a result of anaphylactic shock, the severest allergic reaction, rose seven-fold from 1990 to 2004. More than 30,000 people suffered a life-threatening attack in 2004 – sudden swelling, breathlessness and low blood pressure – of whom half were treated in accident and emergency departments and 3,171 were admitted to hospital.

The most common triggers are insect stings and foods such as peanuts. Anaphylactic shock causes 10 to 20 deaths a year but the figure could be higher because it is often not recorded on death certificates.

What is happening to food allergies?

One of the most extraordinary increases has been in peanut allergy, up 117 per cent between 2001 and 2005. An estimated 25,000 people in England are affected, and many are at risk of a severe reaction if they are exposed to the nuts. The report says up to 7 per cent of infants have a food allergy – many are sensitive to egg, but this tends to improve with age. Among adults, the Institute for Food Research estimates that up to 2 per cent are affected. This is often distinguished from food intolerance which is less specific and thought to be more widespread.

The report says that guidance to pregnant women and children not to eat peanuts should be withdrawn because it may actually be exacerbating the problem of peanut allergy. In parts of Africa, where peanuts are made into a soup used for weaning and in Israel where they are incorporated into a rusk for babies, the problem of peanut allergy does not exist. Depriving children of exposure to peanuts early in life might increase the risk of an allergic reac tion later.

Why are allergies on the increase?

No one really knows. Allergy is an area of medicine more full of puzzles than most. Take hay fever. In 1955, just over five GP consultations in 1,000 were for hay fever. By 1971, the number had doubled and a decade later it had doubled again. Yet this increase was occurring as pollen counts were falling owing to the cut back in agricultural land.

Some specialists have suggested that each age has its defining disease and just as in the late 19th century people claimed to be a "a little bit consumptive", in the late 20th / early 21st century people regard themselves, even proudly, as a little bit allergic. It signifies someone who not only has a medical condition but is sensitive, civilised and responsive to ecological imbalances. There has been disagreement since Victorian times about the roles of mind and body in its genesis, and this continues. But allergy, like hysteria and neurasthenia before it, has come to be seen as an archetypal disease of modern civilisation.

What about the hygiene hypothesis?

This is the leading theory to explain the rise, devised by David Strachan in the 1980s. It can be summed up in a sentence: as we lead cleaner, germ-free lives, and are exposed to fewer illnesses in childhood because of smaller families, our immune systems are under-developed and over-react when exposed to allergens such as grass pollen, house dust mites and cat hairs. The theory has been confirmed by many studies since. Children raised on farms with livestock have a third fewer allergies than those who are not.

However, the theory does not account for the extraordinary increases in allergies such as asthma seen in townships in Tanzania, on Tristan Da Cunha (the tiny island in the south Atlantic) and other parts of the world remote from the infrastructure of developed nations.

How serious is the impact of allergies?

The report quotes this example from an asthma sufferer who wrote: "My quality of life is non-existent. I know this may sound extreme but I would be prepared to lose an arm and a leg if my asthma would go away. I find it really difficult to do daily activities on my own. I don't have enough breath to push a trolley round the supermarket. I am not allowed on an aeroplane and it is impossible for me to get travel insurance. Winter is also a problem – I can't go outside because the cold air sets off my asthma."

Allergy UK said a survey of 6,000 sufferers showed 62 per cent felt their allergy "significantly affected every aspect of their lives." Pupils with hay fever are 40 per cent more like ly to drop a grade between mock exams and GCSE final exams in the summer, when pollen counts are high, than those who do not have the allergy.

What help is available?

Far too little, according to the report. Baroness Finlay of Landaff, who chaired the committee's investigation, said Britain was "the laughing stock of Europe" for ignoring treatments that are routinely available in other countries. Immunotherapy, a powerful treatment for allergy which involves giving gradually increasing doses of the substance which triggers an attack, was abandoned 20 years ago after its misuse led to a number of deaths, but should be re-introduced because it was of proven effectiveness, she said.

Where do we go from here?

There have been three previous reports drawing attention to the lack of services for allergy sufferers – from the Royal College of Physicians in 2003, the Commons Health Select Committee in 2004 and the Department of Health's Review of Allergy Services in 2006 – but very little has changed.

There are 94 allergy clinics but only six are headed by a full-time consultant in allergy. The report says there should be 10, one in each Strategic Health Authority, to serve as clusters of expertise and to provide training for GPs, nurses and schools. An estimated 3 million people consult their GP each year for allergies but knowledge of the problem is "very poor".

Are allergies as serious as they are made out to be?

Yes...

* One in three of the population suffer from an allergic disease at some point in their lives

* There are over 70,000 hospital admissions for asthma and almost 1,000 deaths and over 3,000 admissions for anaphylactic shock

* Peanut allergy has more than doubled since 2001, and 25,000 people are now in danger of a fatal or near-fatal reaction

No...

* Some specialists argue that allergies are a fashionable disease that suggests a sensitive disposition and a reaction of modern life

* Many allergies have minor effects which require only symptomatic treatment and do not interfere with everyday life

* One in five people think they have a food allergy but blind testing shows less than one in 20 actually does