Most people enjoy eating, but for some, food can lead to headaches, nausea, vomiting and even death. There are seven main types of food allergies.

CLASSIC ALLERGY

Cause: The body's immune system mistakes a harmless food molecule for a threatening invader like a virus or bacterium. IgE antibodies attach themselves to the molecule, then signal to other immune cells (mast cells) to attack the molecules by releasing histamines and other destructive chemicals.

Common Culprits: Usually food with large protein particles; 90% of cases involve nuts, shellfish and eggs.

Symptoms: Tingling mouth and lips, rash wheezing, possible vomiting and nausea.

Treatment: Avoid foods which cause it.

ANAPHYLACTIC SHOCK

Cause: This is basically the same as the classic allergy, but the reaction is much more severe and in some cases can lead to death.

Common Culprits: Nuts, especially peanuts, peanut oil and shellfish.

Symptoms: Lips and mouth swell up within seconds of coming into contact with the allergen. Severe rash, throat swells and air passage constricts, causing choking and suffocation. Patient may black out or appear to have a fit and there may be heart failure and circulatory collapse.

Treatment: Avoid known culprits. If eaten by mistake, urgent treatment is required.

FALSE FOOD ALLERGY

Cause: Food triggers the mast cells directly.

Common Culprits: Peanuts, beans, pulses, wheat, eggs, shellfish, pork, strawberries, chocolate, tomatoes, fish, cheese, salami, some wines and beers, sausages, cheese, pickles, broad beans, yeast and avocados.

Symptoms: Headache or migraine accompanied by the symptoms of the classic allergy.

Treatment: Avoid food which cause it.

FOOD INTOLERANCE

Cause: The body is unable to metabolise certain foods because of some physical abnormality, usually lack of a particular enzyme.

Common Culprits: Dairy products, wheat, cereals and alcohol.

Symptoms: Diarrhea, nausea, bloating, flatulence and headaches.

Treatment: In cases of lactase deficiency, use soya milk instead of cow milk. Fermented milk products such as yoghurt and cheese may be tolerated.

FOOD AVERSION

Cause: Dislike and avoidance of a food or foods for purely psychological reasons. This may be due to associating that particular food with a traumatic event or may be part of an eating disorder such as anorexia nervosa or bulimia.

Common Culprits: Meat, fish, vegetables and sweets.

Symptoms: Fear of eating particular foods. A person may alternatively avoid them and then binge on them. The foods may cause nausea on contact or bring about symptoms of sensitivity if knowingly eaten.

Treatment: Psychotherapy to uncover the cause of aversion followed by gradual reintroduction of offending foods.

FOOD ADDICTION

Causes: The body craves one particular food and suffers withdrawal symptoms when it is removed. It may lead the sufferer to eat huge quantities of the addictive food, leading to long-term malnutrition. The condition may be caused by foods that break down in the body to form endorphins or by sugary foods that give a temporary good feeling.

Common Culprits: Cereals, cakes, biscuits, sugar, tea, coffee, dairy foods and chocolate.

Symptoms: Cravings for particular foods, general malaise on withdrawal, long-term malnutrition, weight gain, bad skin, fatigue and mood swings.

Treatment: Remove culprits from diet and gradually reintroduce them at much lower levels.

GENERAL SENSITIVITY

Cause: The cause is unknown most of the time but chemical additives or pesticide residues may be a factor.

Common Culprits: Cereals, dairy products, citrus fruits, coffee, tea, fish, nuts, sugary products, shellfish, chocolate and pulses.

Symptoms: A wide range of gastro-intestinal upsets, skin eruptions, aches and pains, bloating, mood changes and fatigue. Symptoms come and go and may not seem to be closely related to food intake.

Treatment: Adopt a low-allergen diet.