Allergies

An allergy is a hypersensitivity (i.e. an abnormal reaction) to a substance that is ordinarily harmless to most people. Some people are more allergic to certain substances than others - i.e. they have different degrees of sensitivities, depending on the person's threshold.

This hypersensitivity seems to be inherited, as allergic individuals often have allergic parents. Allergic conditions may start early, if one is exposed to the allergens as a young infant. It is also possible for the condition to develop later in adult life.

The substances which trigger the allergic reactions are called allergens. Allergens may enter our body through any one of these ways:

Nose, throat, lungs and eyes- airborne allergens include dust mite droppings, house dust, pollen and pet allergens.

Mouth and digestive system - food allergens (different people are allergic to different foodstuffs)
Skin - dust mite droppings, poison ivy, cosmetics etc.

Tissues under the skin - by injection e.g. animal bites, insect stings or injections.

Allergic reactions include asthma, sneezing, itchy and watery eyes, nasal congestion, coughing spells, itchy skins and nasal discharge. Dust can also make people with asthma suffer attacks like wheezing, coughing and shortness of breath.

What goes on in an allergic reaction?

A typical allergic reaction, whether in the lungs (asthma), in the sinuses (rhinitis), or on the skin (eczema) involves five basic elements: the allergen, the antibody, the mast cells, the mediators (chemical messengers), and the affected organs.

The stages of an allergic reaction caused by airborne allergens are as follows:

1. Sensitization: The allergen enters the body through the mucous membranes of the respiratory system, and is carried to lymph tissue (e.g. tonsils and lymph nodes), where it contacts with lymphocytes, which is a type of white blood cell. The lymphocytes then produces the primary antibody called immunoglobulin E (IgE).
   
   The IgE now attaches itself to the mast cells, which are found in various organs, particularly the nose, lungs, gastrointestinal tract and skin. The mast cells are now sensitized, and will respond to further exposure to the allergen.
   
2. Contact with allergen: The allergen enters the body in future, through the mucous membranes etc, and comes into contact with these mast cells, and their attached IgE antibody. The allergen will then bond with the IgE antibodies.
   
3. Mast cell degranulation: The result is that the mast cells get excited and degranulates, releasing a host of mediators or chemical messengers. These include histamines, leukotrienes, and platelet-activating factor.
   
4. Local allergic reaction: These mediators then circulates throughout the body, triggering the allergic symptoms in the local areas like the sinus, lungs, skin or gastro-intestinal tract.

This is a simplified explanation, as there is a lot more going on behind the scenes in an allergy reaction.

How do I know if I have an allergy?

If you exhibit any of the symptoms described above when you are indoors (especially in the bedroom) or near your pet, you could have an allergy to dust mites or to pet dander. If you have symptoms every time you are near the park or trees, you may be allergic to pollen or grass.

If you think you may have an allergy, consult a specialist. Your specialist may employ a skin prick test, observing your body's reaction to various possible allergens that are introduced to the skin via a "skin prick". The skin prick test is cheap, fast, and accurate, with the results known within 15 to 20 minutes. It is important, however, that you are not on any antihistamines, as these may mask the effect of the allergen.

Most major hospitals and selected private clinics can provide this testing service. Do ask your physician about the test, as knowing what allergens you are allergic to is half the battle won, since you can now target your allergy management programme. Many public hospitals and specialists in Singapore provide allergy tests.

How can I manage my allergies?

Illnesses such as allergic rhinitis, allergic asthma and atopic dermatitis (eczema) are currently managed using a combination of three approaches:

• Allergen avoidance - keeping the allergens away from the patient, so that he does not react to them. Studies have shown that if the patient successfully avoids allergens over a period of at least eight months, his allergic sensitivity will be dramatically reduced - i.e. he will be much less sensitive to the allergens than before, and he will show much less symptoms when exposed to the same allergens as before. That is why this method is gaining popularity in the management of allergies.
  
• Pharmacotherapy - taking prescribed medication, such as antihistamines and steroids.
  
• Allergen-specific immunotherapy - taking "allergy shots" over an extended period.

Of these, avoidance or the shielding of the patient from harmful allergens is potentially the least expensive, best tolerated and the most effective approach for reducing allergic symptoms. Studies have shown that an avoidance regime implemented over a period of eight months can significantly reduce the patient's allergic sensitivity. This is a major approach taken by physicians.

Asthma, diarrhoea, vomitting... could your child be having a food allergy?
- Straits Times, 30 Nov 2002