"I was a bit staggered when I came here and found eight or nine students who were anaphylactic at the school," he says. "I've been a principal for many years and I've noticed that it is increasing more and more."

Although the school's first aid room was always dealing with typical schoolyard accidents — bumps, scraped knees and scratches — it was a niggling concern about the risk of anaphylaxis, a potentially fatal allergic reaction, and other chronic diseases such as asthma that prompted him to act. He went to the school council with an unusual proposal: to hire a school nurse.

Now parents at the school, which has more than 500 students, pay an extra $70 each year to help fund a full-time nurse — a rare appointment in a state school but one that has since been adopted by other schools as they confront a growing number of children with food allergies, asthma and other chronic diseases.

Health experts say that in less than a decade, food allergies in young children have reached epidemic levels, although no one can pinpoint exactly why. Doctors report food allergies now affect up to 6 per cent of children under three. Along the way the list of foods causing allergies has grown, and now includes kiwi fruit, bananas and celery.

A 2010 West Australian-based study found that 80 per cent of schools had at least one student at risk of anaphylaxis. The reality is that many schools have much higher numbers.

Nor is the rising prevalence of nut allergies, which can be life-threatening, a problem just among young children, with research showing teenagers are at the greatest risk of dying from an anaphylactic reaction.

So serious is the issue, kindergartens and schools have been forced to change the way they operate to minimise the danger of at-risk students eating the wrong food. Many have stopped short of banning nuts but peanut butter and Nutella sandwiches — once lunchbox favourites — have all but disappeared from the lunchtime menu as parents become more aware of the dangers. Classes no longer celebrate student birthdays with a cake and teacher treats have lost favour.

Maria Said, president of Anaphylaxis Australia, says Victoria is the only Australian state with laws dealing with anaphylaxis management in schools. It is mandatory for all teachers with anaphylactic children in their care to be trained to understand, recognise and respond to allergic reactions.

Each child at risk must have an individual management plan. A common feature in primary schools now is the picture gallery that lines the staffroom and classrooms to identify students with allergies.

Ms Said says a national approach is needed to improve every school's understanding of allergies and the strategies to reduce risk. While primary teachers can closely monitor younger children by supervising eating times and ensuring they do not share food, she argues such vigilance is more difficult in a secondary setting where students are moving from class to class.

"We've managed to get primary schools to think about this however in high schools there is this mentality that kids should be old enough to look after themselves and that is a real concern," she says.

"We have an increasing number of children with peanut and tree nut allergies reaching the teenage years and we don't currently have high schools that are implementing strategies to assist young people with management."

Doctors say the risk of a severe reaction including death is rare but it is still very real and parents are justifiably alert.

Despite all the safeguards accidents occur, sometimes with tragic results.

This was highlighted this month when Scotch College was found responsible for the death of a student Nathan Francis, 13, by giving him beef satay in his ration pack on a school cadet camp in 2007 despite knowing of his peanut allergy. Victorian Coroner Audrey Jamieson found that the cause of death, anaphylaxis from eating peanuts, was "directly related" to the school's failure to ensure the health and safety of students attending the camp. Nathan's death occurred when there was significant publicity over the death of Alex Baptist, 4, who died after eating peanuts at his kindergarten. Since then, five other teenagers have died from allergic reactions in Australia.

The most recent was a 16-year-old boy in Sydney who died last year after sharing food prepared in a food technology class. He was allergic to walnuts. Many question if that rate would be higher if it were not for the vigilance of parents and teachers and readily available adrenaline.

The most common allergies in children are milk, egg and peanuts, tree nuts such as cashews, wheat, soy, fish and shellfish. Peanut, tree nuts, fish and shellfish allergies are generally lifelong in more than 80 per cent of cases, while children tend to grow out of the others. Mild to moderate allergic reactions can see a child develop rashes or swelling of the lips and face, hives, vomiting and diarrhoea. The more severe form is called anaphylaxis and happens when the airway swells, causing difficulty with breathing, a drop in blood pressure, drowsiness or collapse. People at risk of severe reaction carry a lifesaving dose of adrenaline, usually delivered through an injector such as an EpiPen.

Associate Professor Katie Allen, a paediatric gastroenterologist and allergist based at the Murdoch Children's Research Institute, suspects some teenagers are putting themselves at risk by not disclosing their food allergy.

Despite a five-fold increase in hospital admissions for anaphylaxis in younger children, she says fewer teenagers are being seen in the hospital clinic. "We think kids might be putting themselves at risk in high school because they don't want to admit to having a food allergy," she says. "Anecdotal evidence tells us there is quite a dramatic drop in kids admitting they have an EpiPen between years 6 and 7, it's more than you would expect of them growing out of it."

Professor Allen is leading a study of 10,000 children in years 5-8 called the School Nuts study to try to understand why this age group is taking such risks.

Those with asthma are at even greater risk of having a severe allergic reaction.

It's a worrying trend that Anaphylaxis Australia's Maria Said says needs to be highlighted. "Teens don't want to be different," she says. "While it's cool to carry a mobile or iPod it's not so cool to carry your EpiPen and asking about ingredients when you're out at cafe or school canteen, to be reading food labels. Kids with allergies don't want to be stigmatised or signalled out."

Part of the problem, she says, is community attitude that as they get older they must learn to live and deal with the allergy themselves.

Professor Allen says data from 15 years ago suggested that about 1 per cent of children aged up to three had a peanut allergy. She was surprised to find more than one in 10 children had a substantial reaction to foods often linked to allergies in her recent study involving 5000 12-month-old infants. It partly explains why year-long waits at allergy clinics are now common.

Associate Professor Mimi Tang, director of the Royal Children's Hospital's allergy and immunology department says the rising figures mirror a worldwide trend. The greatest rise appears to be in developed places such as Australia, European countries, the UK and the US.

"Countries that are developing a Westernised lifestyle are showing rapid increases right now," she says. Professor Tang says half of all children in Australia have at least one parent with some form of allergic disease, including asthma, eczema, hayfever and food allergies.

A child whose parents have no allergy problems has a 20 per cent chance of developing an allergy. The risk to a child with one parent with an allergy problem goes up to 40 per cent. When both parents have allergy problems, the risk factor goes up to 50 per cent.

A popular theory about what causes allergies is the hygiene or microbial hypothesis. Exposure to a range of "good" bacteria early in life trains the immune system, the body's department of defence, not to react to common things in the environment such as dust mites and some types of food. More recent studies are focusing on the link between reduced exposure to the sun's ultraviolet radiation and the rise in allergies.

"We are all indoors more and we know that the further you live from the equator the higher the prevalence of allergy problems in that country but what is unclear is whether that relates to vitamin D per se or UV because UV does have immunomodulatory properties," Professor Tang says.

Signs of an allergic reaction

Mild to moderate:

■Hives or welts

■Tingling feeling in or around the mouth

■Abdominal pain, vomiting and/or diarrhoea

■Facial swelling

Severe (Anaphylaxis):

■Difficulty breathing

■Swelling of the tongue

■Swelling and/or tightness in throat

■Difficulty talking and/or hoarse voice

■Loss of consciousness and/or collapse

■Person becomes pale and floppy (infants/young children)

Source: Department of Allergy and Immunology, Royal Children's Hospital.