Allergies are very common, with about a quarter of the population affected at some time in their lives.

THERE are many substances in the environment that our body has to contend with and the number is increasing with mankind’s tinkering. Most of them are harmless. However, there are occasions when particular substances stimulate an altered reaction by the body when it is absorbed.

The person’s immune system recognises a particular substance as a threat (allergen) and initiates a chain reaction. The white blood cells produce antibodies which attach themselves to other cells causing the release of powerful chemicals like histamine. This interaction between the antibodies and allergen results in symptoms. People who are prone to allergies have various symptoms depending on the allergen and the manner in which it is absorbed into the body.

Allergies are very common. It is estimated that about a quarter of the population are affected at some time in their lives. There are studies that report an increase in the number of people affected by allergies over time, such as the number of children affected by nut allergy doubling in a decade. Children who are exposed to secondhand smoke are more likely to develop allergic reactions.

Various reasons have been propounded for the increase in allergies. Some attribute it to pollution. Others attribute it to humans living in a cleaner environment with less exposure to micro-organisms leading to an over-reaction by the body when it comes into contact with allergens.

That scientists have yet to agree on a single theory for the increase in allergies is an indication that more research needs to be done.

Allergens

Allergens are microscopic substances that give rise to an allergic reaction. There are numerous allergens in the environment that can come into contact with the skin and mucous membranes of the body.

A person can be allergic to one or more allergens. The site of the allergic reaction depends on how contact was made with the allergen.

Allergens can be inhaled, such as pollen from plants, moulds, fungi, animal fur; eaten, such as food, milk, nuts, seafood; injected, such as insect stings, medicines; or they can come into contact with the skin or eyes, such as pollen, dust, moulds, animal fur. The common allergens are pollen, dust mites and nuts.

Allergies occur because the body’s immune system perceives an allergen as a threat. White blood cells produce antibodies to defend the body against the allergen. The antibodies produced are similar to the special proteins produced when the body is exposed to micro-organisms like bacteria and viruses. The antibodies adhere to the surface of the allergen.

When the body comes into contact with the same allergen in the future, the immune system produces an antibody called immunoglobulin E (IgE), which causes the release of chemicals from other blood cells including histamine, a protein which is involved in many allergic reactions.

Histamine has widespread actions which are responsible for many of the symptoms of an allergic reaction. It increases fluid release from the small veins, causing swelling of membranes; increases mucus production by the nose resulting in a “runny nose”; causes localised itching and muscle contractions including that of the bronchi leading to wheezing.

People have different responses to an allergen. Some are mild and localised whilst others are more severe and affect more than one part of the body. The symptoms include sneezing, runny nose, wheezing, coughing, breathing difficulties, localised or general swelling, itchy skin, eyes, lips and throat, nausea, vomiting and diarrhoea.

These symptoms are not specific to allergic reactions. They may be due to other medical conditions. It is advisable to consult a doctor when in doubt or the symptoms are generalised or do not go away.

There are rare occasions (less than 1 in 1,000) when an allergic reaction can be life-threatening. This is called an anaphylactic shock, a sudden and severe allergic reaction involving the whole body and usually occurs soon after contact with a particular allergen. Both the cardiovascular and respiratory systems are affected with marked changes in blood pressure and breathing difficulties.

Allergies are not the same as intolerance, for instance, lactose intolerance. When a person is intolerant to certain foods, they can eat a small amount without any problems unlike those who have a food allergy. The latter will develop a reaction with the smallest amount of the food that they are allergic to. Allergies always involve the immune system unlike the intolerance which does not. The former can be detected by allergy tests but not the latter.

Allergy tests

Allergy tests are useful in the precise identification of the allergen. This will facilitate the management of the patient. Allergens can be identified through skin or blood tests.

Patients who are taking prescription medicine for an allergy will be asked to stop all medicines a fortnight prior to the test because the medicines can give a false negative reaction. The skin test involves injecting a very small amount of the suspected allergen into the skin. Alternatively, a patch containing the suspected allergen will be placed on the skin, usually for about 48 hours. The latter test is usually carried out by a skin specialist (dermatologist).

If a person is allergic to the substance, the skin will become red, swollen and itchy. If there is no reaction, it is unlikely that the person is allergic to the substance.

The blood test measures the amount of allergen specific IgE antibodies in the blood that have been produced by the immune system. It involves taking a small sample of blood, usually from a vein in the arm. The results are given on a number scale with zero indicating a negative result and an increasing number indicating an increasing sensitivity to the allergen.

The self-use of some commercial test kits is inadvisable as its quality may not be equivalent to that of scientific standards and there may be problems of interpretation of the result.

The results of allergy tests have to be interpreted by a doctor who has knowledge of the patient’s medical history and clinical presentations.

The most effective way of preventing allergies is to avoid all contact with the allergen. This is easier said than done. Allergens like dust mites or fungus are not easily detectable and can breed even in the cleanest house. Many food allergies are not easily avoided as most people are unaware of the various compounds in the food they are consuming. Pets may also be difficult to avoid.

There are numerous medicines used in the treatment of common allergies. Some are prescription medicines whilst others are available over the counter. The medicines include antihistamines, decongestants, nasal sprays, eye drops, leukotriene receptor antagonists and corticosteroids.

It would be prudent to consult the doctor or pharmacist before taking any of these medicines, as they have side effects.

Hyposensitisation or immunotherapy is a treatment modality used in treating patients who have a specific allergy. The body is exposed to an increasing amount of the allergen over a period of time so that it produces antibodies that will stop future reactions.

This treatment has to be carried out by a doctor because of the risk of an anaphylactic reaction.

Source: Dr Milton Lum