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What is an allergy?
An allergy is a response by the body's immune system to something (called an allergen) that is not necessarily harmful in itself. Certain people are sensitive to this allergen and have a reaction when exposed to it. Some allergic reactions are mild and harmless, but others are severe and potentially life-threatening (anaphylaxis).
What is a food intolerance?
A food intolerance is not the same as a food allergy. Many people incorrectly use the words interchangeably. A food allergy is when the body's immune system reacts
abnormally to specific foods. No allergic reaction takes place with a food intolerance. People with a food intolerance may get digestive symptoms such as diarrhoea, bloating and stomach cramps. These
are quite common symptoms anyway. In food intolerance the symptoms may be caused by difficulties digesting certain substances in food. One example is lactose, a sugar found in milk and dairy
Differences between food allergy and intolerance include:
How common are allergies?
Allergies are very common. About 1 in 4 people in the UK are affected by an allergy at some time during their life. Each year the number of affected people increases.
It is estimated that half a million people in the UK have had an anaphylactic reaction to venom (from bees or wasps). Nearly a quarter of a million people under the age of 45 have had anaphylaxis due to nuts.
Who gets allergies?
Anyone can have an allergy. About half of people with allergy are children. Some people are more prone to allergic problems due to a condition called atopy (see below). Food is a common trigger in children whilst, in older people, medicines are common culprits.
What are the symptoms of an allergy?
Allergic reactions can vary and may include a number of different symptoms. So, with an allergy you may get one or more of the following:
Of course, there are a great many other allergens, too many to list. Most allergens are proteins, but some (for example, medications) are not, and need to be bound to a protein once they are in the body before they can cause an allergic response.
What happens in an allergic reaction?
During an allergic reaction, a complex series of events occurs within the body. These events are co-ordinated by the immune system. Sometimes the immune system 'goes into overdrive'. If this happens, the body can lose control of its vital functions, with catastrophic results. Such a severe reaction can cause death.
An allergen is regarded by the immune system as a foreign substance. When the immune system detects an allergen, it produces an immune system protein called an antibody. Antibodies are also called
immunoglobulin E (IgE). The immune system stores this in its memory (this is called sensitisation). This means that you do not have an allergic reaction the first time you come into contact
with a specific allergen.
If it meets this substance again, the immune system remembers the previous exposure. Antibodies help to attack the invading allergen the immune system believes to be dangerous. A chain reaction is set up whereby other chemicals are released by different blood cells. These chemicals cause the symptoms of an allergic reaction. Histamine is one such chemical (hence, antihistamines are medications often used to counter the effects of an allergic reaction).
Some people get a type of allergic reaction to certain foods that only causes symptoms in the mouth and throat. It tends to cause itching, tingling, swelling of the mouth, lips and throat. Fresh fruit, vegetables and nuts commonly cause this. It can be confused with anaphylaxis. It has thepotential to be serious, as swelling in the mouth and throatcan affect the ability to breathe, but this is rare. The symptoms start within minutes of eating and tend to settle completely within an hour. An ambulance should be called immediately if you feel faint, have difficulty breathing or feel like your throat is closing up.
Anaphylaxis is a life-threatening allergic reaction. It is a medical emergency. If you suspect someone has anaphylaxis, you should dial 999 for an ambulance.
The symptoms of anaphylaxis include:
Look to see if the person is wearing a MedicAlert® bracelet or necklace. Are they carrying an adrenaline pen (EpiPen®)? If they are, you could save their life by administering it.
Some families seem particularly prone to allergies. They have a condition known as atopy and are hence known as atopic individuals. People in atopic families can develop problems such as asthma, eczema and hay fever. It is an inherited problem and these people are more likely to develop an allergic disorder. Atopic individuals seem to produce more of the antibody IgE, related to allergic reactions.
It is more useful to prove a suspected allergy, rather than to screen randomly for any allergy. This is because virtually anything can potentially cause an allergic reaction.
There are an infinite number of allergens - certainly too many to test for. Most allergy tests involve testing for a few common allergies.
Current media attention seems very focused on allergies and intolerances. It is true that, as a nation, allergic disorders are becoming more common, and we are not exactly sure why. However, many people seem keen to diagnose themselves with allergies and intolerances. There are many unscrupulous (non-medical) individuals who are prepared to charge money for unproven, unscientific 'tests' to 'prove' such problems.
If you suspect you have a specific and significant allergy, you should discuss this with your doctor. Commercial allergy testing kits are not recommended. This is because they are often of a lower standard than those done by reputable clinics. Do not waste money on private non-medical testing, particularly tests bought from the internet or tests that involve analysing hair or electrical impulses in the fingers. Many people have been incorrectly diagnosed with allergies and intolerances this way, and, as a result, exclude foods from their diet unnecessarily. Sometimes this can put their health at risk.
Blood tests can be done in some circumstances, for some suspected allergies. They are sometimes called radioallergosorbent testing (RAST). The tests measure the amount of IgE antibody (the
immunoglobulin protein made by the immune system) in the blood that has been produced against a suspected allergen. RAST is scored from 0 to 6, depending on the amount of allergen-specific IgE. A 6
means that there is an extremely high level of IgE for that allergen, so the person is very sensitive/allergic to that allergen.
Blood tests are safer in cases where a person has had a very extreme allergic reaction, such as anaphylaxis. Skin prick testing in these people would be potentially dangerous. Blood tests for allergies can be carried out whilst people remain on antihistamine medication (skin prick testing cannot), so it is useful if people have such severe symptoms that they cannot stop their medication.
Your medical history, symptoms and previous allergy reactions will guide us on arranging the appropriate screening tests for suspected allergies.
If further investigations are needed (prick or patch skin tests etc.) we will refer you for specialist assessment.
Information provided by www.patient.co.uk