Allergy

An allergy is an abnormal reaction or increased sensitivity to certain substances. The allergic individual produces symptoms when exposed to these substances, and these substances would normally be harmless to non-allergic people.

The main reason for this is that allergic people make a special type of antibody called Immunoglobulin E (IgE) which can react with environmental substances in a harmful way. These substances are known as allergens.

The reaction between allergens and IgE antibodies causes release of substances such as histamine which produce allergic symptoms in the skin, the nose, the eyes, the chest, etc.

The most common allergens are found in connection with handling animals, pollens, house dust, house dust mites, molds, some drugs and many foodstuffs, especially fish, eggs, milk and nuts. Bee and wasp stings may cause allergic reactions and occasionally these stings can have fatal results.

Additionally, feathers, wool, dyes, cosmetics and perfumes may sometimes act as allergens.

Common Allergies

Allergic reactions or diseases may involve any part of the body, the most frequently involved being the nose and chest with symptoms resulting such as hay fever, rhinitis or asthma. The skin and eyes also commonly show allergic symptoms. Anaphylactic shock is severe allergy which affects many organs at the same time. This can cause a rapid decrease in blood pressure, fainting and, occasionally, death. Such reactions though, are rare.

Hay Fever

If you suffer from hay fever, the pollens of grasses, weeds and trees are the main causes of this type of allergy, although mold spores can also cause the symptoms.

The lining of the nose becomes swollen and exudes a runny discharge. Spells of sneezing and itchiness of the throat and palate also occur and the eyes may be similarly affected. Depending on where you live and the pollinating periods, attacks may occur in spring, summer or autumn.

In perennial allergic rhinitis, the symptoms are similar to hay fever but appear all the year round. This condition is caused by non-seasonal allergens such as house dust components and certain molds.

See Also: Hay Fever Programme

Conjunctivitis

You are more likely to suffer from an allergic condition of the eyes as an adult. Allergic conjunctivitis is often associated with allergic rhinitis. A general complaint is of itchiness of the eyes, which are rubbed frequently - adding to the problem.

Asthma

If you are asthmatic, you can suffer from attacks which obstruct the flow of air to the lungs. Breathing becomes difficult and forced breathing becomes necessary. A wheezing sound appears, due to the rush of air through your narrowed airways. At the same time, a troublesome cough can develop. Asthma may begin at any age and, if neglected, tends to recur and become chronic.

Asthma may be allergic or non-allergic in origin. In allergic asthma, environmental allergens trigger the disease when inhaled or ingested.

See Also: Asthma Health Advice

Eczema

If you suffer from eczema, your skin can become irritated and develop rashes which can be either wet or dry and occasionally chapped. The reactions are often accompanied by severe itching. The cause is often not clear, but is frequently seen in children of families with a history of allergic diseases. The eczema usually starts during the first year of life, on the face. Later, it is often seen on the inside of the elbows and backs of knees, on the neck, on the ankles, on the wrists and on the back of the hands. Most cases of eczema disappear during the teens.

See Also: Eczema Health Advice

Nettle rash (Urticaria, Hives)

This reaction appears very suddenly. Your skin becomes warm, reddish and itching. The symptom may last either for a couple of hours or up to a whole day.

Contact Eczema

With contact eczema, your symptoms will be similar to those of the eczema previously described, but the allergic reaction is of another type. The cause is direct contact with different substances, such as:

Nickel (in coins, stainless steel, clasps)
Chromium (in cement, leather)
Rubber products (in gloves, boots).
Preservatives (in creams, ointments and cosmetics)

Food Allergy

The stomach and the digestive system are also frequent targets for allergic disease.
Your symptoms in this case are caused by allergy to foods. This can result in vomiting, stomach pains, diarrhoea or constipation. Frequently, eczema and hives may be produced after ingesting food to which you are allergic.

Food allergy may also trigger asthmatic attacks and, rarely - generalised anaphylaxis.

Insect Allergy

Severe allergic reactions to bee and wasp stings are not uncommon. The local toxic reaction and discomfort that usually occurs following an insect sting is not generally considered to be allergic. IgE mediated (allergic) reactions induce symptoms such as nettle rash (Urticaria, hives), running nose and eyes, swelling of the throat, attacks of asthma and, in severe cases, fainting.

Should you be highly sensitive to bee or wasp stings, you may become unconscious within a short space of time. Immediate action should be taken to get you expert medical treatment, preferably at the nearest hospital.

Occupational Allergy

The term occupational allergy is generally used to describe episodes of allergic reactions occurring after working with industrial dusts, vapors, gases or fumes. Furthermore, substances like nickel (in coins), chromium (in cement), rubber, different dyes, formaldehyde and glues may result in eczema which occurs at the site of contact with the skin.

The degree of eczema depends on the length of exposure and sensitivity to the substance. Symptoms may show within some weeks, but it can often take months, years, sometimes decades, before an eczema develops. Any part of the skin may become affected, but the most frequent sites are the hands, arms and the face because these tend to be the least protected parts of the body.

Allergic Mechanisms

Allergy is an unusual reaction or sensitivity to substances that do not trouble most people:

IgE Mediated Allergy

Following exposure to common environmental allergens, the allergic individual produces a special type of antibody, called Immunoglobulin E, or IgE.

The healthy individual has a very low level of IgE in the blood, while those with certain allergic conditions such as hay fever, allergic asthma, and some forms of eczema, have high IgE levels.

In the human body, certain cells called mast cells and basophils are involved in allergic reactions. IgE, produced as a result of repeated allergenic stimulation, attaches to the surface of these cells and subsequent binding of the allergen triggers a biochemical reaction, leading to the release of different substances. These substances cause a build-up of fluid in the tissue, and contraction of the smooth muscles. Depending on the route of entry of the allergen and where the reaction takes place, different symptoms will occur.

If the reaction takes place in the nose and eyes, hay fever will result -- while asthma is the result if the chest is affected. Eczema appears when the skin is affected.

Non IgE Mediated Allergy

Mechanisms other than IgE can trigger an allergic response resulting in symptoms in various organs.

Sometimes, especially if asthma starts in adult life, no apparent cause can be found. Usually, the first outbreak of symptoms follows an infection which may have been either bacterial or viral in origin.

The common cold, cold moist weather, smoke, chemicals and psychological or physical stress can be responsible for episodes of this type of asthma.

Most occupational allergies, such as contact eczema, are not IgE mediated.

Who Becomes Allergic?

Anyone can develop an allergy, but the probability is increased if one or both parents suffer from some kind of allergic condition. Indeed, the presence of another allergic individual in the family is the strongest factor for predicting allergy in a child. However, even when both parents are affected, that does not necessarily mean that a child will be.

Diagnosis

It is essential for successful treatment, that the allergens responsible for the symptoms are accurately identified. There are different ways to arrive at a diagnosis. The case history is extremely important in all allergy investigations. Based on what the patient tells about his/her symptoms, the doctor decides what tests should be carried out.

Patient Case History

The case history should form the basis for all allergy investigations. In order to give the doctor an idea of the mechanisms and allergens causing the trouble, the doctor will question the patient or ask him/her to fill in a questionnaire.

It is important to know when and how the symptoms developed. Also important is the relationship to seasons, damp weather, physical activity, certain foods, etc. Knowledge of personal habits such as smoking, occupation, hobbies, etc., will be necessary and some information about the home can be important (e.g., whether there are pets, or fitted carpets in the house or if cleaning aggravates symptoms). A favorite cologne or perfume can be the cause of allergic conjunctivitis, whilst a soap may be the cause of chronic eczema.

In nasal allergies, the case history alone may give enough information to settle the diagnosis and the doctor can then decide which measures to take to help the patient. In more complicated cases, however, further investigations have to be performed to get a final diagnosis.

Skin Tests

Skin test procedures are used by many doctors to identify allergens responsible for the symptoms. There are several methods of skin testing.

Drops of the suspected allergens are put on the skin of the forearm and the skin is either pricked or scratched (prick or scratch test) through the drops. Suspected allergens can also be injected into the skin of the back (intradermal skin test). After 15-20 minutes, if there is an allergy to one or more of the substances, a round wheal with a flare forms on the spots where the substances were injected. This may identify and confirm the allergy.

However, besides causing the patient some trouble, the intradermal skin tests are not very reliable. Drug treatment for the allergic symptoms in the 24 hours prior to the skin test may invalidate the results, and skin testing in small children is both inconvenient and unreliable.

Patch Tests

Patch testing is used in the investigation of allergic contact eczema. The test is performed by using a small piece of blotting paper moistened with the suspected substance or a prepared strip containing various standard allergens. The paper or strip is taped to an area of healthy skin for 24 or 48 hours.

If you are allergic to the substance tested, eczema will be seen where the test substance has been in contact with your skin.

Provocation and Elimination Tests

These tests are performed in the eyes and nose in hay fever sufferers, but in the airways in asthmatics.

A highly diluted allergen extract is dropped into the nose or eyes or is inhaled. The test is continued in this way, using more concentrated allergens until the allergic symptoms are provoked. This shows that the tested allergen is responsible for the patient's symptoms.

When allergy to food is suspected, different foods (usually those most commonly associated with allergy) are eliminated to see if the symptoms disappear. They are re-introduced into the diet, one by one, to see if any of them causes a return of the symptoms.

The skin and provocation tests, apart from being inconvenient to the patient, have other disadvantages. The bronchial provocation test is not without risk, and may be influenced by medical treatment and the physical and mental condition of the patient.

Laboratory Tests

IgE plays an important role in allergic rhinitis, allergic asthma and in some forms of eczema. Detecting and accurately measuring the amount of IgE is, therefore, of great importance when diagnosing allergies.

Because of the limitations and disadvantages associated with skin and provocation tests, there has been a need for more convenient and reliable methods. Today, there are laboratory tests available that accurately measure IgE, and a small blood sample is sufficient for allergy testing.

These tests measure either the total amount of IgE in the blood, which indicates if your symptoms are of allergic origin; or specific IgE, which tells the doctor which allergens are causing the trouble.

Due to their ease of use, reliability, convenience and accuracy, these tests have become routine and form an important part of the diagnostic work.

Treatment

With all allergies, it is necessary for successful treatment, that the allergens are accurately identified. There are three main objectives in the management of allergic disease:

To eliminate causative factors from the immediate environment, where possible
To reduce irritation in the tissue (i.e., to treat the symptoms with different drugs)
To decrease immunological reactivity by vaccination (specific hypo sensitisation)

Your Thoughts and Questions

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