The Charity for Environmental Illness

Allergy or Intolerance?


The difference between food sensitivity, allergy and intolerance can be confusing so each term is briefly described here. The advice on this website is not intended for people suffering from true food allergies as they need to completely avoid their allergens. If you suspect you may have a true food allergy (as explained below) see your GP.

Food Sensitivity

Food sensitivity is a phrase used to describe both food allergy and food intolerance. Its precise meaning varies according to different practitioners and authors. Some doctors only use the term to describe food intolerance. Others use it to describe reactions that are an exaggeration of normal side effects to the chemicals in foods, such as histamine or salicylates. On our website the term 'food sensitivity' is used to encompass any adverse reaction to food, ie both allergies and intolerance.

Food Allergy

The word 'allergy' is commonly used to refer to any unpleasant reaction to a food or other substance. However, in the medical profession, the term has a more specific meaning and is used to describe a particular reaction of the immune system to a usually harmless substance. Some practitioners only use the term to describe reactions involving the Immunoglobulin E (IgE) antibody. To differentiate it from food intolerance reactions, food allergy is often referred to as a 'true' or 'classic' food allergy. Precise terminology varies between practitioners.

Unlike food intolerance, food allergy can easily be diagnosed with a variety of tests. If you suspect you may have a food allergy, consult your GP for testing as soon as possible. Testing is likely to involve either a skin prick test or a RAST blood test to measure IgE antibodies.

Food allergies can start at any age and can last from several years to a lifetime. As reactions can be so extreme, it is vital to avoid all traces of the problem food. A food allergy can occur after contact with minute quantities of the allergen by ingestion, contact or inhalation. Reactions are usually (but not always) immediate and can be mild or severe, ranging from headaches and rashes to vomiting, breathing difficulties and collapse.

Anaphylactic shock is a sudden, severe allergic reaction that involves the whole body. It usually happens within minutes of coming into contact with the allergen, but can occur up to 2 hours later. Because it involves the breathing and circulatory systems, anaphylactic shock is life-threatening and requires immediate medical treatment. Some of the first signs can be a feeling of warmth, flushing, tingling in the mouth or a red, itchy rash. It can cause symptoms such as light-headedness, shortness of breath, severe sneezing, anxiety, stomach or uterine cramps, vomiting and diarrhoea. In severe cases patients could experience a drop in blood pressure, resulting in shock and loss of consciousness. This sort of reaction does not usually occur with food intolerance, so if you are in any doubt, seek immediate medical help.

Please note - the information on this website is not relevant for individuals with true food allergy as such people need to avoid their allergens completely. Food rotation will not alleviate true food allergies.

Food Intolerance

Food Intolerance is a term used to describe a reproducible, adverse reaction to a specific food or ingredient that occurs even when the food is eaten in a disguised form. Food intolerance differs from food allergy mainly because of the lack of evidence of a specific IgE immune reaction.

The body's reactions to food intolerance are not well understood, and therefore there are currently no medical tests available in surgeries. Doctors usually rely on patient diaries to diagnose food intolerance, although some patients prefer to try non-medical testing.


Unlike food allergies, intolerance reactions are not set off by minute quantities of food, such as from a badly washed spoon. They can, however, be triggered by relatively small amounts, and also by smells. Reactions can occur at any point between the food being eaten and excreted, therefore symptoms are extremely wide ranging and can vary in severity from day to day.

Because there is no typical set of reactions or medical test, many doctors remain sceptical about the existence of food intolerance. There are, however, certain conditions that are widely recognised.

A GP should be able to rule out any of the following types of intolerance or refer you to a specialist who can. Treating such conditions can often greatly improve food intolerance:

  • The body over-reacting to naturally occurring chemicals in foods such as histamine or salicylates (often referred to as food sensitivity).
  • The body lacking certain digestive enzymes, as in gluten and lactose intolerance.
  • A porous or 'leaky' gut wall allowing undigested particles of food to pass straight into the bloodstream.

Food intolerance can begin at any age. It often starts imperceptibly, with symptoms worsening over several years and culminating in general poor health. However, it can also be triggered suddenly by a viral infection, illness or other stress that weakens the immune system.

Many people have up to five intolerances - usually to their most frequently eaten foods - but hypersensitive sufferers can become intolerant of all foods if their condition is not managed properly. This type of extreme multiple food intolerances or even total food intolerance is especially common amongst sufferers of ME and Multiple Chemical Sensitivity. In some cases, it has been directly linked to severe Candidiasis (yeast infection).

Although a small proportion of food intolerances are lifelong, most will disappear when the offending food is not eaten for a few months. Conversely, such intolerances are likely to recur if the food is ever eaten again in excessive amounts. There are instances (often in children), where food intolerance resolves itself. This is usually as a result of dealing with underlying health problems and strengthening the immune system.

Print Email