All about Allergy?


What is an allergy?

It's a type of inflammation that takes place when the body comes into contact with certain substances in the environment. These substances are called allergens (to denote that they cause an allergy) and they can be just about anything – a toxin from an insect sting, a food ingredient, an animal product (fur, dander) or a plant product (especially pollen).

These substances cause inflammation. But an allergy is different from the inflammation caused by germs like bacteria and viruses, or by heat, chemicals or physical injury.

Allergy involves a certain set of reactions by the body's immune system, specifically types of white blood cells called 'mast cells'. These release chemicals such as histamine and immunoglobulin E antibodies, which act together to produce an allergic response such as tissue swelling, increased amounts of fluids, redness and itching. This is sometimes followed by inflammation in the tissues, where white cells from the blood are attracted into the tissues.

This clinical definition of allergy is different from that used by lay people,who often use the word 'allergy' to describe an intolerance or other bad reaction to a substance. But a true allergy is an inflammatory reaction that involves histamine and IgE. After exposure to an allergen, the response – the allergic reaction – is usually quick, within minutes (though it's possible for the inflammation to be chronic, and ongoing, for example in the bowel).

Allergic conditions

What symptoms and conditions the allergy causes depend on where the allergic reaction takes place in the body and what tissues are affected.

The most common allergic conditions include:
  • Asthma – a condition in which the airways become inflamed and constricted leading to difficulty breathing and wheezing. Take a look at the asthma fact file for a full run down.
  • Rhinitis (hay fever or perennial allergic rhinitis) – this means inflammation of the nose, the sinus passages, throat, ears, and the conjunctiva (tissues covering the whites of the eyes). Symptoms include runny nose, sneezing, red watery eyes and sinus headache. The trigger is not always hay or grass; dust mite protein, moulds and pet dander can trigger allergies that occur all year around.
  • Urticaria (hives) – if the skin reacts to an allergen it may become red, raised and itchy with wheals and blisters of varying size that can last from minutes to weeks. The problem with hives is only some are triggered by allergies. In fact, the most common cause is infection, particularly in young children.
  • Eczema – dermatitis (inflammation of the skin). It's also called atopic dermatitis, atopic eczema or allergic dermatitis. Take a look at the eczema fact file for a full run down.
  • Food allergy – some people can have allergic reactions to certain foods such as peanuts, tree nuts, milk, eggs, wheat and seafood. Food allergies can cause skin rash or hives or in severe cases vomiting, breathing difficulty or even collapse.
  • Insect allergy – bees, wasps and ants are the most common causes of insect allergy in Australia. Insect allergy reactions can be just as serious as those triggered by food allergy and can include hives and breathing difficulty. Fortunately, local swelling is much more common.
  • Anaphylaxis – is a serious, general, sudden, sometimes life-threatening collapse that can be caused by food, insect stings and medicines (most commonly pain killers and antibiotics). The allergic reaction causes the blood vessels to suddenly dilate leading to a catastrophic drop in blood pressure, or it can make the airways contract, making breathing difficult or sometimes both. When someone with anaphylaxis has a serious reaction they need immediate treatment in the form of an injection of adrenaline (as in an EpiPen) and emergency medical treatment. While it's terrifying and potentially dangerous, deaths from anaphylaxis are not common and people generally survive if they get the emergency help they need.

Often people change their allergy patterns as they go through life and it's hard to predict how someone will react when they're exposed to an allergen. Food allergies and eczema are most likely to develop in infants, asthma in young children, and rhinitis in older children and adults.

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How are allergies diagnosed?

Often people can self-diagnose and manage a simple allergy, such as hay fever.

But if this doesn't help or the symptoms are serious then it is important to see a GP, who will take a history and conduct any relevant physical examination. If they can't diagnose your condition they will refer you to an allergy specialist or immunologist.

To help determine the allergen a doctor will ask what happened prior to symptoms occurring. Sometimes the allergen is obvious, as in many cases of asthma or hay fever – a person may start sneezing or wheezing every time they come near a horse, for example.

But in other cases, food allergies or eczema, for example, it's not so obvious if it's an allergy or what the allergen is.

It's possible to identify an allergen by testing.

Skin prick testing involves introducing a tiny amount of a potential allergic trigger into the skin. If the person is allergic to one or more allergens then they will have a characteristic reaction – the area around the injection site will become red and raised.

Blood tests are needed when people have eczema, anaphylaxis (specialists will not want to expose these people to their allergen), cannot come off antihistamines (antihistamines affect the accuracy of skin tests) or have a history of allergic symptoms but test negative with skin prick testing.

If you have contact dermatitis your doctor may do patch tests, for more information about this read our fact file on eczema and dermatitis.

But be careful; there are a lot of allergy tests on the market such as cytotoxic food testing, kinesiology, Vega testing, electrodermal testing, pulse testing, reflexology and hair analysis that are not scientifically proven.

How are allergies treated?

The best way to deal with an allergy is to avoid what triggers it. No exposure to the allergen; no allergic response.

In some cases it's easy. If you're allergic to cats, avoid cats.

But sometimes it's not so easy. People may not know what they are allergic to, or it might be impossible to avoid the allergen, for example pollen during spring. In these situations treating the symptoms is the best option. Taking medications will help relieve the symptoms or 'dampen down' the allergic reaction.

Medication

Symptomatic treatments include antihistamines (taken in a nasal spray, eye drops or tablet), corticosteroids (in nasal sprays, puffers, skin creams and ointments, but not normally as tablets), bronchodilators (drugs that expand the airways given by puffer). If you have anaphylaxis you'll need to carry adrenaline with you all the time in case you have a severe reaction.

Some of these medications may have side effects, for example taking antihistamines orally can cause drowsiness.

Desensitisation

Providing the allergen is known another option is to 'desensitise' the immune system to the particular allergen. This process is called immunotherapy and involves exposing a person to increasing doses of an allergen over time. This is typically done via injections or high doses of oral extracts placed under the tongue.

The idea is the immune system becomes used to the allergen and no longer provokes an allergic response.

Immunotherapy can be expensive and time consuming (it may take months or even years) and often doesn't work, or works only temporarily – eg for one spring/summer season – so you need to weigh up whether it's worth it. It tends to work best for asthma and rhinitis and people with severe allergy to insect stings. It is a form of therapy used when people have bad allergies when medicines don't work or as an alternative to medication. Besides, many allergies last for years and the cost of medicines can also add up. Unfortunately it does not yet help food allergy, but this is an active area of research.

Managing your allergy

Most people manage their allergies through a combination of avoiding their known allergens where possible and using treatments to relieve the symptoms. While not the ideal solution it can help most people manage to get their symptoms under reasonable control.

There is no way of curing an allergy but there are things you can do to reduce the risk of having an allergic reaction, these include:

  • Breastfeed your infant for the first 4 – 6 months if possible – infants who are breastfed have fewer allergies.
  • Don't smoke during pregnancy or in the presence of a child.
  • Develop an action plan to manage your or your child's allergy. An action plan can help people manage their allergies such as what medications to take and when and what to do in the event of a medical emergency. Most people diagnosed with asthma or anaphylaxis will be given an action plan by their doctor.
  • Educate your friends, family, school staff and community about your allergy (or your child's allergy). They play a vital role in helping avoid allergy triggers and can get help in an emergency.

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Posted By: tajuddin3/28/2010 Total views: 9985


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