In the British Medical Journal, Professor Nicholas Christakis of Harvard Medical School claims that parents are in the grip of "nut hysteria" as an "epidemic" of irrational fears about children having allergic reactions to peanuts spreads. The situation is now so fraught in the US that a school bus was evacuated and decontaminated after a peanut appeared on the floor. According to Christakis, our "gross overreaction" to nuts is making allergies worse: avoidance of potential allergens may actually make children more sensitised, because they never get a chance to build up a tolerance to them.

So how common is the allergy among UK children? A House of Commons report in 2004 suggests that the figure may now be as high as one in 50 - that's a quarter of a million children. But before we panic, says Christakis, it is worth putting this into perspective: around 150 Americans (adults and children) die from food allergies each year, compared with 50 killed by bee stings and 100 struck by lightning. What's more, each year around 10,000 children are admitted to hospital for traumatic brain injury after playing sport - nobody is planning to ban that. So before you turn your house into a nut-free zone, here are some practical ways to establish whether your child really is allergic:

1. Look for an immediate reaction: the sudden release of chemical substances, including histamine, from cells in the blood and tissues where they are stored, can cause a combination of symptoms: facial, lip or throat swelling, rashes that appear and spread quickly, breathing difficulties (from mild wheezing to gasping) and a difficulty speaking. Young children can become unresponsive and "floppy". There may also be abdominal pain, nausea, vomiting or diarrhoea, or a sudden feeling of weakness (caused by a drop in blood pressure). There is usually some combination of these symptoms.

2. Note repeated reactions: "A food allergy is very reproducible," says Vicky Field of the Anaphylaxis Campaign. "So every time the food is ingested these signs will appear."

3. Listen: "Often a child's complaints about a particular food will be your first sign that something is wrong," says Field. Especially if your child says a food makes them hurt, perhaps pointing to the throat or mouth.

4. Examine your family: around 7% of people with peanut allergies have a sibling with one too, and about 50% have a sibling with some other allergy, according to Anaphylaxis Campaign figures. It is also worth knowing that children with asthma are more likely to have a severe reaction if they have a nut allergy. The good news is that an allergy might not last: one in five children will outgrow their nut allergy by the time they go to school.

5. Get a diagnosis: many parents try to diagnose allergies themselves using the internet or tests offered by alternative therapists. These are notoriously inaccurate. The most reliable way to tell whether your child has a nut allergy is to get a referral via your GP to an allergy clinic, ideally to see a paediatric allergy specialist. This is absolutely worth it if your child is showing the signs above - children who have only had mild reactions to nuts can still have a severe, even life-threatening reaction at some point. A specialist will take a detailed history and do either a skin-prick test (where they put traces of nut on a needle and watch for the reaction) or a blood test. Diagnosis is never 100% accurate but the combination of methods will give a very good indication.

• For more information, contact the Anaphylaxis Campaign: 01252 542029, anaphylaxis.org.uk