Six-year-old Sarah was swinging on the shopping trolley, impatiently watching her mother choosing fruit and vegetables, when she suddenly felt a tightening in her chest. When her mother turned round she saw her daughter, face bleached white, clutching on to the bars of the trolley. By the time they had reached home and called the doctor, Sarah was fighting for breath. Now 22, Sarah still remembers her first asthmatic attack. “I felt as though I was drowning, I couldn’t breathe. I still recall the fear and panic.”

Asthma is the most common chronic condition among children in the western world. In the UK, it affects at least one in eight young people under 16, who account for about half of the three million sufferers here. It’s hardly surprising, then, that an average-sized primary school class is likely to contain at least two pupils who suffer from asthma. But, despite its prevalence, it can go undiagnosed for years.

Robert, born in 1983, spent three years of his childhood with a persistent cough. “Still coughing,” his mother would say at each consultation with the GP. After many prescriptions for cough medicines or antibiotics, the doctor eventually diagnosed asthma. Robert’s cough stopped after appropriate treatment.

The typical symptoms of childhood asthma are a persistent cough, wheezing, shortness of breath and tightness in the chest. The persistent cough was once often diagnosed as bronchitis or another chest infection. But GP Sean Hilton, chair of the educational committee of the National Asthma Campaign during the 1990s and now professor of primary care at St George’s hospital medical school in London, says there is less delay in diagnosis these days. “A lot of guidelines have been published for doctors, schools and parents - everyone is now more aware of the varying symptoms of this disease and how it should be treated.”

Asthma is a chronic inflammatory disease that causes the airways to narrow, making it difficult to get air in and out of the lungs. The inflammation, caused by chemicals released from white blood cells that infiltrate the lungs, may also increase the production of sticky mucous or phlegm, and make the small muscles surrounding the airways twitchy or sensitive. In response to certain triggers such as allergens, cold air or stress, this increased sensitivity - called bronchial hyper-reactivity - makes the muscles around the airways tighten, causing wheezing and coughing. While allergens in animals, plants, dust and foods are well-known triggers - some people blame dairy products for their attacks - more common in children are a reaction to cold weather, exercise, tobacco smoke, excitement or an emotional upset. No one knows why some children develop the condition - or why it is two to two and a half times more common in boys than girls - but the greatest risk factor appears to be genetic.

And it can be a killer. Four Weddings and a Funeral star Charlotte Coleman, who died earlier this month, is one of the 1,500 who die following an attack each year, 25 of them children under 16. Figures released by the British Thoracic Society last week show that in 1999 lung disease (including pneumonia, TB, lung cancer and asthma) killed 153,000 people - more than either heart disease or other cancers.

Most children with asthma have a family history of asthma, eczema or allergies such as hay fever. But genes are not entirely to blame. In identical twins (who have identical genes), the incidence of the disease in both twins is only about 30 per cent. And the increase in asthma cannot be attributed to significant changes in the gene pool. In just 25 years the number of cases has doubled - far too short a time for any significant genetic shift in a population.

What about environmental factors - air pollution, exposure to allergens such as house dust mites and pets, and exposure to industrial and agricultural chemicals? No one knows to what extent these are risk factors, but passive smoking and chest infections are known to increase the likelihood of developing the disease. Some people believe the falling number of childhood infections and rise in allergy levels are also significant.

Inhaled steroids - usually given by a brown inhaler - reduce the inflammation. Depending on the severity of the disease, children will need between one and three doses a day. Bronchodilators, also inhaled, relax the muscles surrounding the airways so they become less constricted and make breathing easier. But bronchodilator drugs (in a blue inhaler) do not treat the disease; they simply relieve the symptoms. Thus children must inhale their steroids regularly - even though they do not bring about instant relief of wheezing, chest tightness and breathing difficulties.

An alternative approach involves using drugs, known as leukotrienes, which block the action of inflammatory chemicals. These drugs are not yet licensed for treating children “but they may prove useful for those with mild to moderate asthma because the drug is taken by mouth and only once a day”, says Dr Hilton. Typically, children develop asthma between the ages of five and seven; the peak age range is between seven and 10 years. It usually disappears around puberty but persists into adulthood for about 20 to 25 per cent of sufferers.

Asthma needs to be treated, and it is important that children take their medicines as directed. This used to cause particular problems in schools when children were not allowed free access to their medicines. But the efforts of the National Asthma Campaign and others have raised the profile and knowledge of childhood asthma, and most pupils now have access to their drugs, while teachers or first-aid officers are trained to cope with emergency attacks.

Nevertheless, teachers are not obliged to help children take their medicines. Recently revised guidelines issued by the National Association of Head Teachers state: “Heads should be most reluctant to accept any responsibility for the administration of medicines to pupilsI where any aspect of administration is crucial to the welfare of the child.”

School policy actually forbids Melanie O’Donnell, a first-aid officer in a south-west London primary school, from giving medicines to her pupils. “We put the children’s inhalers in a cupboard each morning and they can help themselves if and when they remember or need them,” she says. She is not even allowed to administer a bronchodilator when a child is having a severe attack. “We can only sit them on a chair with their arms crossed on a table in front of them and try to keep them calm until their parents or an ambulance arrives (see box).”

The rising incidence of asthma is costly. Prescriptions alone cost more than pound;500 million, and the cost to the National Health Service and the Department of Social Security (in invalidity payments), as well as to business through lost productivity, is estimated at more than pound;1 billion a year. Childhood asthma accounts for only a small proportion of this sum, but it is likely that the number of children who develop persistent asthma into adulthood will increase.

ASTHMA: HOW TO FIGHT BACK

* Make sure the child uses his or her reliever inhaler immediately. This device, which usually comes in a blue plastic holder, opens up the narrowed air passages.

* Stay calm and reassure the child. This is important as attacks can be frightening. Listen carefully to what the child is saying. It is comforting to have a hand to hold but do not put your arm around his or her shoulders as this can be restrictive.

* Help the child to breathe slowly and deeply. Most children find it easier to sit upright or lean forward slightly. Lying flat on the back is not recommended. Loosen any tight clothing and offer a drink of water.

* Minor attacks should not interrupt school involvement. The child can go back to normal activities as soon as he or she feels better.

* Inform the parents about the attack.

* In an emergency, call a doctor or ambulance if the reliever has had no effect after five to 10 minutes, if the child is distressed, unable to talk or is becoming exhausted, or if you have any doubts about his or her condition. Give reliever medication every few minutes until help arrives. Never take an affected child to hospital by car as his or her condition may deteriorate very quickly.

This information is taken from the National Asthma Campaign’s school pack. Tel: 020 7704 5853. National Asthma Campaign, Providence House, Providence Place, London N1 0NT. Website: www.asthma.org.uk.A National Asthma Campaign helpline staffed by asthma nurse specialists is open Monday to Friday, 9am-7pm. Tel: 08457 010203. The campaign will also help parents and teachers set up “junior asthma clubs” which are for four to 12-year-olds. Tel: 020 7704 5839