Allergies are adverse reactions of the immune system caused by substances that are usually harmless (allergens). Allergens contain protein and the most common are house dust mites, pollen and pet hair. Allergies can cause symptoms of sneezing, itchy eyes, hives, sickness and breathlessness. Allergy symptoms are usually mild but severe reactions can cause serious medical problems.

Causes

Allergies occur when the body comes into contact with a harmless substance (an allergen) that it believes is invading it resulting in a hypersensitive reaction. The immune system releases the immunoglobulin E antibody (IgE) to defend the body which in turn releases other chemicals. These chemicals, one of which is histamine, combine to cause symptoms of irritation and inflammation. If a person has a food allergy, the antibody IgG is released.

People can be predisposed to allergens due to family history and their condition is called Atopy. Atopy means the individual's body produces higher levels of the IgE antibody. Environmental factors can increase the chances of atopy if a child grows up in house of smokers, pets, excessive dust mites or if they are taking antibiotics.

There are thousands of allergens including dust mites, pollen, animal fur, grass, insects, milk, eggs, peanuts, tree nuts, fruit, latex and certain medications (penicillin, aspirin, codeine).

Symptoms

Allergic reactions do not occur during the first contact with an allergen as the body must first develop sensitivity to it. Allergies can trigger a number of symptoms together or individually. The most common are: sneezing, coughing, wheezing, runny nose, sore throat, sinus pain, rashes, hives, vomiting, itchy eyes, breathlessness and swelling.

Allergies are not the same as an intolerance to a substance. Allergies involve the immune system and can be tested by immune responses to allergens. Allergy tests will not highlight intolerances (such as lactose intolerance or other food intolerances).

Diagnosis 

Allergies are typically diagnosed using allergy intolerance testing and should be carried out by a trained professional. Home allergy testing kits are generally of a low standard and not recommended. The most common allergy tests are the blood, skin prick and patch tests.

The 'challenge test' is another method and is usually carried out in a hospital or specialist allergy unit. Challenge tests involve introducing allergens to the lung (in the case of bronchial allergies such as asthma), nose or eye. Food allergies can also be identified using a challenge test whereby the patient is given specific foods 'blind' to observe their effects.

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*Source: GoToSee.co.uk

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