One in five UK adults believes they have a significant food allergy. Most don’t – the best estimates suggest that 1.5-3.8% of adults and 6-8% of children have food hypersensitivity (FHS) which is a food allergy or intolerance. But real food allergies can be severe and life-threatening, so expert diagnosis and advice are essential.

What is an allergy?

Allergic reactions involve a response by the immune system: immediate responses involve IgE antibodies and occur within minutes of eating or even touching the substance you’re allergic to (the allergen).

A delayed response (4-28 hours) is called non-IgE mediated allergy. Allergic symptoms can range from mild to life-threatening anaphylaxis. Common symptoms are sneezing, itchy and runny eyes and nose, wheezing, chest tightness, cough, swollen lips, tongue, eyes and face. You may feel sick, get stomach pains or vomit.

What is anaphylaxis?

Anaphylaxis is an extreme and severe allergic reaction affecting the whole body. It usually starts within minutes of exposure; common culprits are tree nuts, peanuts, sesame, eggs and shellfish, while drugs such as penicillin, wasp and bee stings and latex are also dangerous for some.

If you have a significant reaction to a tiny amount of the allergen, react to skin contact with it or have had a severe allergic reaction in the past, you should see your GP and request referral to an allergy clinic or specialist testing. If you’re at risk, you should carry an auto adrenaline injector. There are around 20 deaths per year in the UK attributed to anaphylaxis, most of which are potentially preventable.

What’s the difference between a food allergy and intolerance?

“Intolerances are different to food allergies – they are not caused by the immune system and are not life threatening,” says Amena Warner, head of clinical services at AllergyUK. Intolerances usually affect adults, rarely infants, who are more likely to have an allergy. The most common symptoms are gastrointestinal – bloating, wind or loose stools.

Other symptoms may be rashes, joint pains and headaches. There are no validated tests for food intolerances other than lactose.

How can I find out if I have a food intolerance?

Food intolerances can be diagnosed with the help of a registered dietitian by cutting out the suspect food, waiting for symptoms to improve and then gradually reintroducing while monitoring the symptoms. A food diary, to correlate what you are eating with symptoms, is useful. If cutting out the food has no impact, there may be an alternative diagnosis such as irritable bowel syndrome. Tests for lactose intolerance are not usually necessary and NHS provision of the tests is often limited to specialist centres.

I used to be able to drink pints of milk, but now I can’t. Why is that?

Many people have a partial lactose intolerance and find they can eat a certain amount of dairy but get stomach ache and bloating if they overdo it. Lactose is mostly found in dairy and is added to foods such as bread, cakes and dressings. The enzyme lactase breaks it down into two sugars that can be easily absorbed from the gut into the bloodstream.

In humans, lactase activity declines after the age of 35. If there isn’t enough lactase to digest the amount of lactose we eat, it sits in the bowel, fermenting. Significant lactase deficiency affects about 5% of the UK population and is usually genetic and lifelong. In parts of the world, such as China and Japan, where adults haven’t eaten dairy products for many generations, lactase deficiency rates are much higher. Food poisoning or a tummy bug can cause a temporary lactase deficiency in anyone, especially in children, and can last up to six weeks.

When can I give my child peanuts?

Sooner rather than later. Israeli kids are 10 times less likely to develop peanut allergy than comparable (Jewish) kids in the UK. This is almost certainly because many Israeli kids eat a peanut-based snack called Bamba. A recent study confirms that early exposure to peanuts reduces the risk of developing an allergy in later childhood. Another study for the Food Standards Agency last week suggested that giving common allergenic foods to children from three months may dramatically reduce the risk of allergies to those items in later life.

A child may inherit a predisposition to allergic conditions (eczema, asthma, hayfever, specific allergies); a tendency known as atopy. If there is a strong family history of atopy, NHS advice is to breastfeed for six months if possible and introduce solids gradually. If the baby has an allergic reaction to a food, it must be avoided, of course. But avoiding potential allergens such as peanuts does not seem to be warranted and may even increase the risk of an allergy developing.

My baby cries incessantly. Could she have a cow’s milk allergy?

“Cow’s milk protein allergy occurs in up to 5% of infants and toddlers, and usually disappears by the time they are around five,” says dietitian Tanya Haffner. “It is unusual for milk allergy to last into adulthood. It requires a completely dairy-free diet, which should be undertaken with advice from a medical professional.” Lactose intolerance in children is usually transient, after a tummy bug or as a consequence of an underlying disorder like coeliac disease, according to Haffner. But a report in the BMJ says there has been a trend to “inappropriate diagnosis” of lactose intolerance in unsettled babies, resulting in treatment with lactase or a lactose-free formula milk. Mums who are breastfeeding and suspect cow’s milk allergy in their unsettled baby can try cutting out milk and dairy products to see whether it helps.

I’ve heard you can be treated for allergies by desensitising injections

“Desensitisation to food is not currently available and is only being tested and trialled under research conditions in specific allergy centres,” says Warner. Desensitisation (or immunotherapy) involves giving gradually increasing doses of extracts of the allergen as an injection or under the tongue. It can only be carried out in clinics with resuscitation equipment in case of life threatening anaphylaxis. The best approach to allergies is to identify the culprit, avoid it and carry oral antihistamines for use in mild cases and injectable adrenaline for severe cases. Wearing a bracelet with details of your allergy may be helpful if you are at risk of anaphylactic shock.