Oral itching and tingling
These symptoms are characteristic of many food allergies, but when they appear in the absence of other, more severe reactions (wheezing, dizziness, vomiting), they might indicate oral allergy syndrome (OAS) - a little-known but common response to a number of raw fruits and vegetables, experienced by up to 20% of hay-fever sufferers. Allergy to birch pollen, for instance, which causes spring hay fever, often triggers perennial oral allergies to carrot, celery and apple, due to the presence of related allergens. "We've only recently woken up to the problem," says allergy dietitian Isabel Skypala, of the Royal Brompton hospital, London.
Headaches and migraines
These have many causes - such as dehydration, caffeine withdrawal, stress - but studies from the allergy unit at Royal Prince Alfred hospital in Sydney indicate that additives and other, naturally occurring, chemicals in food may sometimes be culpable. Researchers took 100 migraine patients, put them on a low-chemical elimination diet for three weeks, then challenged them with various additives. More than two-thirds reacted to monosodium glutamate and food preservatives, and there were significant responses to amines (found in chocolate, mature cheese and red wine) and colourings, too. Dr Howard Dengate, of the Food Intolerance Network in Australia, says the results challenge the assumption among many complementary therapists that wheat and dairy are prime culprits in migraine. "The perceived benefits of removing wheat and dairy from the diet are more likely to be due to the exclusion of preservatives and additives in processed food," he says.
A key symptom of serious food allergy is acute wheezing, which is especially alarming in patients with underlying asthma. Chronic asthma, although not caused by food sensitivity, can be exacerbated by it. Wheezing triggered by sulphite preservatives (found in dried fruit, prepacked salads and tinned or processed food) is widely acknowledged. Respiratory symptoms while preparing raw vegetables - such as potato, chard or carrot - can signify OAS, the culprit allergens becoming airborne and inhaled when peeled, chopped or cooked.
"Frothy" diarrhoea can indicate lactose intolerance - an inability to digest the milk sugar in dairy foods (many IBS sufferers find symptoms improve on adjustment of their cereal fibre intake). Digestive problems can also indicate coeliac disease - an auto-immune condition whereby a component of gluten (a protein complex in wheat, rye, barley and oats) triggers the production of antibodies that precipitate tissue damage in the gut. According to Coeliac UK, 1% of the population has coeliac disease, with up to half a million undiagnosed. Symptoms vary, but "gut symptoms are common", says Dr William Dickey, consultant gastroenterologist at Altnagelvin hospital, Londonderry. "Patients might have abdominal bloating, wind, vague indigestion or heartburn. A quarter endure diarrhoea, which is a classic symptom but, conversely, I've seen coeliac patients with constipation, too."
Acute urticaria - or "nettle rash" - is a common response to a food allergy. However, food-induced eczema in infants is actually relatively rare: according to one study, about 7.5% of cases may be provoked by cows' milk protein - and the role of food in adult eczema appears less significant. Another skin condition, dermatitis herpetiformis (DH) - characterised by red patches and blisters, typically on the elbows, knees and buttocks - is a symptom of coeliac disease. "In some cases," says Dickey, "DH may present in the total absence of any gastrointestinal symptoms."
When food proteins are digested they're converted first into peptides and then into amino acids. In those with compromised digestion, this second stage can be inefficient. "In some people, the problem lies in a failure to properly digest food and keep larger [undigested] food particles out of the bloodstream," says nutritionist Patrick Holford, an authority on food allergies. "These foods can not only cause symptoms, but also may become craved, or even possibly addictive, because peptides, such as those derived from wheat and milk proteins, can have a morphine-like effect in the body. This may be why some people feel worse in the early days of removing an allergen from their diet."
Tired all the time
A common 21st-century malaise, with a selection of possible causes. There are suggestions that the laborious digestion of foods to which an individual is sensitive may induce lethargy when large reserves of energy are diverted towards the straining digestive system and therefore away from the rest of the body. Fatigue brought on by either iron deficiency or megaloblastic anaemia is a feature of around a third of undiagnosed coeliac patients, according to Dickey, because tissue damage in the small bowel reduces absorption of iron, folate and vitamin B12.
· Living With Food Allergy, by Alex Gazzola, is published by Sheldon Press, priced £7.99.