Some primary schools are banning foods and even separating children at lunchtime as they deal with more pupils with food allergies.

Allergies to nuts, eggs, wheat and kiwifruit are on the rise, leaving principals and teachers monitoring children for any signs of an allergic reaction.

Exposure to the slightest trace of peanut can send an allergic child into anaphylactic shock, causing abdominal pain, bloating, vomiting, diarrhoea, itchy and swollen skin.

In severe cases they find it difficult to breathe as their throats and lung walls swell.

However, allergy experts warn that banning such food makes staff and students complacent and could put children at higher risk.

Based on British and Australian figures, an estimated 6 to 8 per cent of New Zealand school children have some sort of food allergy.

Milk is one of the most common, followed by eggs and peanuts. Other common allergies are soy products, fish and shellfish.

Auckland's Balmoral School has 22 pupils with a potentially fatal peanut allergy.

A picture of each of those children with their allergies listed is pinned on staffroom walls.

Each child's EpiPen, which administers a shot of adrenaline if the child goes into anaphylactic shot, is stored in a filing cabinet.

Teachers have not yet had to give an injection, but every year staff are trained by a public health nurse in what to do.

The school has decided not to ban peanuts or peanut products. "You can't enforce it and I could not police it," said principal Malcolm Milner.

It has a policy that children are not allowed to share food, and those with the most severe allergies are monitored by a teacher aid.

At Ponsonby Primary, principal Anne Malcolm and her staff monitor 14 children with nut allergies.

Like Balmoral, the school has not banned peanuts or nut-based foods. "I don't believe in making policies; that just gets everyone's backs up," said Malcolm

Staff are trained how to use an EpiPen, which has to be jabbed into a child's thigh and held there for 10 seconds.

Ken Pemberton, principal of Murrays Bay School, said staff patrolled the school grounds to watch children at lunchtime. Nine of the school's 575 students have a peanut allergy.

"Some of these kids we're told have only got a minute before they can have permanent brain damage," said Pemberton. "It is increasing and it frightens some teachers - the responsibility is enormous."

At Papatoetoe Central School in South Auckland, the new entrants have sanitiser sprayed on their hands before eating. The school has also asked pupils not to bring peanut butter sandwiches for their lunch.

Principal Marilyn Gwilliam said that, with wiping down classroom tables, this helped protect an allergic child from nut traces.

In Wellington Paremata and Wadestown Schools banned nuts in 2008. The ban includes peanut butter, Nutella and any cakes, biscuits, muesli and chocolate bars containing nuts.

But Allergies New Zealand chief executive Penny Jorgensen said food bans made it harder for children to learn to manage the condition.

Danger by the dozen

Mum Julie Hancock knew there was something wrong when she gave her baby son Nathan a piece of egg.

"He vomited it up straight away and turned bright red."

Nathan was showing the classic signs of a child with an egg allergy. Tests proved Julie's suspicions and from then on the family and staff at his daycare centre had to be careful there were no eggs around him.

Last September he started at St Thomas's School in Auckland's Kohimarama.

While there is no egg ban at the school, his teachers plan to ban the use of egg cartons in case they carry traces. The school also does not allow children to share their lunches.