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Allergy, airborne


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Immune system
The body's immune system is designed to protect against infections or substances that may cause harm. An allergy is an over reaction by the body's immune system to substances that are usually harmless. When this over reaction occurs, the person is said to suffer an allergic reaction. The substances that are capable of triggering these allergic reactions are called allergens, and they are of many varied types. Some allergens are carried in the air, for example grass and tree pollens, spores from fungi, and fur or hair from animals such as cats, dogs and horses. Other allergens are present in what we eat or swallow, for example shellfish, strawberries or medicines, while some people are allergic to bites and stings from insects.

Here, in this section, the discussion will focus on allergens that are carried in the air, the so-called airborne allergens.

The airborne allergens are important as the allergic reaction may eventually lead to the child developing asthma.
An allergic reaction does not occur the first time that a child is exposed to the allergen. It has to be exposed two or more times. This process is known as sensitisation and, after it has developed, the child is said to have become sensitised to the allergen.

During the sensitisation process, when the allergen first comes into contact with the body's immune system, special proteins are produced against the allergen by the immune system. These special proteins, called antibodies or immunoglobulins (IgE) are highly specific to each allergen, capable of recognising just that allergen. More and more IgE is produced each time the immune system is exposed to the allergen, eventually excessive amounts of IgE circulate in the blood stream. When an allergen now enters the body, its binding to IgE causes the release of large amounts of histamine and other chemicals from cells called mast cells. It is the release of these chemicals that cause the symptoms of an allergic reaction. The release of histamine from mast cells in the nose causes sneezing and a runny nose, while the release of histamine from mast cells in the eye will cause the eyes to water and appear red.

Symptoms of an allergic reaction correspond with the area of the body affected by the mast cells releasing their chemicals in response to IgE. If it is the nose, symptoms include a blocked or runny nose, sneezing and itching. A wheeze may also be heard and felt if the cells lining the lungs are involved. If in the eye, the eyes will water and appear blood shot. If in the skin, an itchy red rash may appear.

While many of these symptoms may be similar to a cold or an infection, they differ in that the discharge from the nose and eyes is clear and watery, and unlike the green, thick discharge of a cold which also tends to occur in the presence of a raised temperature.

If your child has developed an allergy the simplest way of reducing the problem is to try and first identify the allergen and then reduce the child's exposure to it. For example, if moulds are suspected keep rooms well ventilated and remove any signs of black mould growing on the walls. If pets are a problem, try to confine the pet to certain areas of the home away from bedrooms and living rooms. Vacuum clean regularly, wash bed linen and soft toys to reduce house dust mite. Keep windows closed if the pollen count is forecast to be high. In severe cases air purifiers may be used.

The symptoms of allergic reactions can be controlled with a variety of medicines, including antihistamines, corticosteroids, cromoglicate and montelukast. Antihistamines act by counteracting the histamine that is released from the mast cells during an allergic reaction. They are useful for reducing symptoms such as sneezing, runny nose, watery eyes and skin rashes. There is a variety of antihistamines available, some will make your child sleepy and these are called sedating antihistamines, for example alimemazine, chlorphenamine, hydroxyzine, ketotifen and promethazine. The advantage of this type of medicine is that it may help your child sleep if the allergy is keeping him or her awake. Other antihistamines, called non-sedating antihistamines, should not make your child drowsy or sleepy. Non-sedating antihistamines include cetirizine, desloratadine, fexofenadine, levocetirizine, loratadine and mizolastine.

Corticosteroids have a useful role in the prevention of allergic reactions by helping to reduce the immune response to allergens. Corticosteroids include beclometasone, betamethasone, budesonide, flunisolide, fluticasone, mometasone and triamcinolone.

Cromoglicate helps stabilise the mast cells against IgE, preventing the release of histamine and other chemicals. Montelukast opposes the action of some of the chemicals released from the mast cells.

All of these medicines are produced in an number of different forms, for example nasal sprays for allergic rhinitis (runny nose), eye drops for allergic conjunctivitis (watery eyes), creams for skin symptoms, tablets and liquids for symptoms affecting several parts of the body. The age range of children in which they can be used varies. Many are not suitable for use in young children. You will need to check with your pharmacist or doctor which product is suitable for the age of your child.

In severe cases of allergy that have failed to respond to anti-allergic drugs, allergen immunotherapy may be used to reduce the immune response. These include desensitising vaccines and a drug called omalizumab.

Allergen immunotherapy with desensitising vaccines involves giving a course of increasing amounts of the allergen to which the child is sensitive. This procedure appears to desensitise the immune system, reducing the extent of the allergic reaction the next time there is natural exposure to the allergen. Omalizumab is an antibody that binds to IgE reducing the amount available to trigger an allergic reaction. Omalizumab is given by injection, the number of injections depending upon the amount of IgE present in the blood stream. With both procedures there is a risk of causing a severe, life-threatening allergic reaction, called anaphylaxis. Children requiring allergen immunotherapy must be referred to a hospital specialist experienced in the technique and with facilities to resuscitate the child if a severe reaction takes place to the vaccine.
When to consult your pharmacist
There are many over the counter remedies available without a prescription for the relief of symptoms associated with airborne allergens. Tell the pharmacist the age of your child and describe your child's symptoms. The pharmacist will recommend a product suited to the child's age and symptoms.
When to consult your doctor
If you suspect that your child has developed an allergy, speak to your doctor. Your doctor will examine your child and ask you to describe when the symptoms appear. If the doctor needs to confirm that your child has an allergy, a blood test may be performed to detect levels of IgE.

Also, if you know that your child has an allergy but your find that over-the-counter remedies do not help, see your doctor who may decide to put your child on a course of corticosteroids or to prescribe medicines that interfere with the immune response to the allergen. If the allergy is severe, your doctor may decide to refer your child to a hospital specialist for allergen immunotherapy.