My mid-life allergy crisis: Can you suddenly become allergic to something or is it all in the mind?

Having never had an intolerance to food, Dan Roberts suddenly started experiencing symptoms at 40.

I have long been sceptical of people claiming they had a food allergy. These days, it's all lactose-intolerant this and gluten-substitute that. Surely, I thought, the whole idea of food allergies and intolerance was just a "read-it-in-the-papers-so-I-must-have-it-too" scenario.

The figures certainly bear this out. One in five of us thinks we have a food allergy, but a 2008 survey by the Food Standards Agency found that only one in 70 UK adults has a genuine, or "classic" allergy to food – most commonly to peanuts and tree nuts (walnuts and hazelnuts), shellfish and fish, but also to cows' milk, eggs, soya and wheat.

A classic food allergy can be a serious business. A morsel of your allergy-producing food triggers the immune system, which mistakenly believes that food to be harmful and produces antibodies, which bind to "mast cells" in the eyes, nose, throat, lungs, gut, cardiovascular system and skin. At subsequent exposure to the same food these mast cells will release chemicals such as histamine, leading to swelling, itching and flushing in the skin; vomiting and diarrhoea; coughing, wheezing or a runny nose; swelling of the lips; and sore, red and itchy eyes.

These reactions happen within a few minutes of eating the food and, at worst, entail a severe, whole-body reaction called anaphylaxis, which can be fatal.

An intolerance, on the other hand, is far more common (around 10-15 per cent of Northern and Western Europeans have a dairy intolerance). Those affected have varying degrees of difficulty digesting certain foods. The most common culprits are lactose, a sugar found in dairy products and gluten, a protein found in cereals and grains.

But my scepticism took a knock when I researched a piece about dairy allergies in children and realised that many of the symptoms – eczema, acid reflux, rhinitis, bloating, gas and digestive problems – were ones I had been ignoring for more than a year. I had these symptoms daily, had never had them as a child, but was soldiering on. So, this summer, I found myself describing my symptoms to Dr Rita Mirakian, consultant in allergy and immunology at the London Allergy Clinic. She immediately thought an allergy was unlikely: "In adults, milk allergy does exist, but is not common. The majority of adults who react badly to dairy have an intolerance, because they lack an enzyme critical for the absorption of that particular food."

So if I was intolerant to dairy, I was probably just consuming too much. As a tea/coffee/cheese fanatic, I was at the thick end of the dairy-consumption scale. But what of late-onset allergies – do they happen? "Absolutely," said Dr Mirakian. "I have a 90-year-old woman who developed an anaphylactic reaction to peanuts at the age of 84." It's hard to say why an allergy, or indeed an intolerance, develops in later life, but it may be linked to infections, illness and lifestyle, which can weaken our digestive systems. Stress may also be a culprit, as may airborne pollution or the many chemicals to which we're exposed on a daily basis.

To eliminate any chance of an allergy, Dr Mirakian first took a medical and symptom history and then gave me one of the two gold-standard allergy tests: "skin-prick" tests for the common allergens (pictured, left). This is a key point, skin-prick and blood tests are the only clinically proven allergy tests. In the skin-prick test, a drop of common allergens – dust mite, cat, dog, allergy-producing fungi, milk, egg, wheat and oat – was placed on my forearm, then the skin pricked to allow the allergen to penetrate my skin. If the skin pricking triggered a red lump and itching, I would have been allergic, but there was none.

To check for an intolerance to dairy, I was put on a three-week "exclusion" diet, which involved removing every trace of dairy from my diet, then reintroducing them in a four-day "challenge" of a pint of milk a day. If the symptoms returned, an intolerance would be likely. So, did my symptoms subside? Not really. I was gassy and bloated. My acid reflux bubbled. I coughed and my eczema got worse. At least my nose stopped running.

The first thing I realised was how much dairy (and wheat) I consumed. The second was that dairy products are everywhere. Crisps! Olive oil spreads! Sausages! Non-dairy creamer! I used soya milk in my tea (passable) and cappuccino (disgusting).

I gazed longingly at shelves laden with brie, cheddar and parmesan in supermarkets. I ate pasta without grated cheese (dull) and eschewed my beloved pizza. All for nowt. Back in Dr Mirakian's office, she confirmed that allergies were definitely out and a serious dairy intolerance unlikely. Could it be wheat, then, I asked? "The only way to check is to eliminate wheat and put it back again – and if you found dairy hard to give up, wheat is far more difficult," she replied. "Instead, you should reduce the wheat and dairy in your diet, especially foods that ferment, like cheese, bread and alcohol."

I had hoped for a simple solution. I contacted Jos Swinger, a nutritionist. He picked up on the fact I had gone through recent periods of stress.

"The more stressed you are, the less likely you will be to digest sugars such as lactose, in dairy," he said. He stressed that, when reducing the amount of dairy or wheat in your diet, it's vital to replace one food with another. So cow's milk can be replaced with soya, oat, rice or almond milk; wheat products such as bread with starchy vegetables.

For a final opinion I turned to Lindsey McManus of Allergy UK. "It is very difficult to pinpoint intolerances," she said. "You may be intolerant, or you might just be a bit under the weather. Either way, it's often a good idea to cut back on wheat and dairy. Most people in the UK eat far too much of both. It's easy to eat toast for breakfast, a sandwich for lunch and pasta for dinner – that's three wheat-based meals in a day. If we all varied our diets more and ate more healthily, many of these problems would sort themselves out."

www.londonallergyclinic.com; www.allergyuk.org; Jos Swingler: www.bespokenutrition.com

Do you have an allergy?

A true or "classic" food allergy is estimated to affect one in 70 adults.

It's more likely to be food intolerance – 10-15 per cent of northern and Western Europeans have a dairy intolerance.

A true allergy involves an immune-mediated reaction to a particular food (various nuts, fish and shellfish).

An intolerance does not involve the immune system and is an inability to digest a particular food.

There are only two clinically-proven tests available: an IgE blood test and a skin-prick test.

The only clinically proven test for intolerance is exclusion or elimination, with the suspect food removed from your diet for a few weeks, then reintroduced.

Dairy

Lactose intolerance occurs when your body can't digest the sugars in milk. It can result in eczema and digestive problems

Nuts

Allergic reactions to nuts can vary from mild to very severe, and are sometimes life-threatening

Wheat

Coeliac disease is a gut disorder caused by gluten (a protein found in wheat, rye, and barley), which damages the intestine. About one in 100 people in the UK have coeliac disease

Seafood

An allergy to fish may begin in childhood and is likely to be lifelong. People allergic to one type of fish or shellfish are often advised to avoid all kinds of seafood