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Allergy
What is an Allergy? An allergy is not a disease in the typical sense. It's a condition that occurs when the body 'misreads' a harmless substance such as pollen, animal dander, certain foods or drugs as being potentially dangerous to the body. As a result it causes the body's immune system to be activated.
The Allergic ProcessThe allergic response takes place in an allergic person when he or she is exposed to an allergen. An allergen is a substance that is normally harmless to the body e.g. animal fur, pollen, shellfish, nuts. In an allergic person, their immune system recognizes a harmless substance or allergen to be potentially dangerous to the body.
Types of AllergensTwo types of allergens are differentiated and include:- Indoor allergens
- Outdoor allergens
Indoor AllergensThese include the like of house dust mites, feathers, cat and dog dander, cockroaches and mould. These allergens normally cause allergy all-year-round.
Outdoor AllergensThe major form of outdoor allergen is pollen. The 2 major sources of pollen allergy are trees and grasses. As a result, in South Africa we experience 2 pollen seasons:- A tree pollen season
- A grass pollen season
| TREE POLLENS | GRASS POLLENS | | | Season | Season | | Mid July – end September | October - May | | | Allergenic Trees | Allergenic Grasses | | Willow, Oak, Plane, Port Jackson | Rye grass, wheat, maize, kikuyu, Bermuda |
Initial Exposure to an AllergenBefore an allergic response can take place, the body must be exposed to a particular allergen. On an initial or first exposure to a particular allergen e.g. a pollen grain, specific 'allergy' antibodies called IgE are produced. These circulate throughout the body and attach themselves to cells called mast cells which are located in the skin, nasal lining, lungs and other tissues.
The Allergic ResponseOnly on a subsequent exposure to the same allergen will an allergic reaction take place. This allergic response takes place when an allergen binds to the IgE antibodies that are already situated on mast cells. This binding or linkage causes the mast cell to burst open and to release chemicals such as histamine.
Histamine then binds to specific receptors in the body called H1 receptors. On binding to these receptors, symptoms such as itchy, watery eyes, itching skin and runny nose take place.
Types of Allergies
Respiratory Allergies
Allergic Rhinitis or Hay Fever:Allergic rhinitis or hay fever is a form of allergy that affects the nose and sinuses where it causes inflammation, swelling, excessive secretions and itching. This occurs when allergens such as house dust mites, mould, pollen, dog/cat or other animal dander are inhaled.
 The illustration showing typical allergic rhinitis or hay fever symptoms.
AsthmaAllergic asthma is one form or type of asthma. Exposure to common allergens such as pollen, animal dander, mould and house dust mites can trigger an allergic asthma attack.
Typical hay fever symptoms are:- Breathlessness
- Wheezing
- Tightness or soreness in the chest
Skin AllergiesHives or urticaria are the types of skin allergies that result from exposure to allergens. This results in an itchy rash that is characterised by small bumps that can expand as the allergic reaction progresses. Scratching can lead to the release of more histamine and consequently more hives.
Food AllergiesTrue food allergies only affect about 1% of adults. What many refer to as a food allergy is in actual fact a food intolerance. Food intolerance produces symptoms such as nausea, diarrhoea and abdominal pain. Food intolerance does not involve the immune system where as true food allergy does.
Food allergies can trigger anaphylactic shock. This is a rare, life-threatening allergic reaction that occurs in people sensitive to a particular allergen. A sudden but severe lowering of blood pressure occurs with constriction of the airways.
Medication AllergiesAllergic reactions to medicines are serious as they can lead to anaphylactic shock. Medication such as penicillin, cephalosporins or sulphur containing drugs are most likely to cause this life threatening reaction.
Insect Venom AllergiesSome people are allergic to the venom injected by certain insects during a bite or sting. Bee, hornet and wasp stings tend to be more serious than other insect stings and can also be life-threatening.
Environmental AllergiesEnvironmental allergies refer to those caused by pollen, house dust mites, mould or animal dander. Allergic rhinitis, asthma and atopical dermatitis are common types of reactions to these allergens.
For people who suffer from these types of allergies, it is important to minimize exposure.
Differentiating Between Symptoms
Differentiating Between a Cold, Flu, Hay Fever and SinusitisThe common cold, flu, hay fever and sinusitis all share many common symptoms. However, the successful recommendation of an OTC (over the counter) product depends on one's ability to distinguish one condition from the other. The following table gives guidelines as to how one can help distinguish one condition from another:
| SYMPTOMS | COLD | FLU | HAY FEVER OR ALLERGIC RHINITIS | SINUSITIS | | | Fever | |  | | May be low grade | | Runny nose/mucous | | | | Thick, yellow-green | | Nasal congestion/stuffy nose | | | | | | Itchy eyes/nose/ear canal | | | | | Develops following a
respiratory condition | | | | | (often develops following an infection or allergy) | | | Facial pain | | | | |
Although allergic rhinitis is not a fatal disease it can cause considerable illness and suffering and impact on an individual's quality of life.
Avoiding Allergens
Allergen Avoidance and Environmental ControlAvoidance of allergens reduces symptoms and medication requirements and is the first priority in patients with moderate to severe symptoms of allergic rhinitis.
Although it may be possible to avoid allergens such as food allergens, allergens produced by pets etc., it is almost impossible to avoid aeroallergens such as house dust mites and pollen. However, one can reduce one's exposure to these allergens.
House Dust MitesMites are mainly found on bedding and carpets and avoidance should therefore concentrate in these two areas.
Some factors that can be employed to avoid house dust mites are the following:- Reduce house dust mite reservoirs. Remove dust collecting items e.g. carpets soft toys and thick curtains
- Decrease indoor humidity. Air conditioner in summer and heater in winter
- Kill live mites. Regularly wash (weekly) rugs and blankets at high temperatures i.e. 55 °C and put items such as these in the sun
AnimalsAnimals such as cats, horses, dogs and birds are common sources of allergies. Domestic furred animals are also a common source of allergens as an allergic individual has continuous exposure to them. If an individual is allergic to an animal, the best solution is to remove the pet; however, this is not always that easy.
If it is not possible to remove the dog or cat:- Wash cats regularly
- Keep the dog strictly outdoors and away from the allergic patient
PollensPollens produced by grasses, trees and weeds are a common source of allergies. Generally pollens rise with the heat to high levels during the day.
As the temperature begins to cool during the afternoon, their levels start to decrease. Highest pollen exposure is encountered in the late afternoon.
The following factors can be employed to reduce exposure to pollens:- Not cutting the grass
- Wearing sunglasses when outdoors
- Keeping bedroom windows closed especially on windy spring days
- Keeping car windows closed, when in the car
MouldsThese organisms are often found in damp areas of buildings, particularly basements, bathrooms and upholstered furniture.
The following factors may reduce an individual's exposure to mould:- Solve problems of dampness inside a house
- Excessive humidity may be reduced with an exhaust fan
- Clean and disinfect tiles, shower curtains, plumbing fixtures and bathroom ceilings with Jik, Milton or Lysol
- Limit indoor plants
Over The Counter Treatment
OTC (Over-The-Counter) Treatment of AllergyAntihistamines are commonly used in the treatment of allergic conditions. They exert their effects by blocking histamine from combining with specific histamine receptors knows as H1 receptors which are found in the small blood vessels of the skin, nose and eyes.
Histamine's Action on the BodyWhen histamine combines with H1 receptors it causes the following effects:- Dilation or swelling of the blood vessels
- Constriction of the airways
- Inflammation and swelling of tissues and possible itchiness
- Increased production of watery secretions of the eyes and nose
How Antihistamines Work
 The British Medical Association New Guide to Medicines & Drugs 2001: 123-125
By blocking the action of histamine, antihistamines:- Reduce redness (preventing dilation of the blood vessels)
- Reduce watery discharge
- Sneezing
Types of AntihistaminesTwo types of antihistamines are differentiated:- Older antihistamines
- Newer antihistamines
Older Antihistamines:The older antihistamines are known as non-selective H1 blockers. This means that they are not selective for blocking H1 receptors only but also block cholinergic receptors in the parasympathetic nervous system. Since these agents block both H1 and cholinergic receptors, they are able to relieve rhinitis symptoms associated with allergy and infections such as colds and flu.
Because these agents block cholinergic receptors as well, they may also be associated with so-called 'cholinergic' side effects, which include:- Blurred vision
- Dry mouth
- Difficulty passing urine
Many of these older antihistamines also show significant signs of drowsiness. This is because these drugs can cross the blood brain barrier readily. Interestingly histamine, found in the brain, is responsible for alertness.
Furthermore, these agents tend to have a short duration of action and are consequently administered 3 to 4 times daily.
Examples of Older Antihistamines Include:- Chlorpheniramine maleate
- Mepyramine maleate
- Buclizine hydrochloride
For more information on these treatments please contact your healthcare professional.
Newer Antihistamines:The newer antihistamines are far more selective for H1 receptors than any other receptors. For this reason they can only be recommended for treating allergy symptoms and are not effective in treating cold or flu symptoms.
Compared to the older antihistamines, they also have a prolonged half-life, which facilitates the convenience of a once daily dosage.
Furthermore, they do not cross the blood brain barrier readily and therefore are less likely to cause drowsiness.
Examples of the Newer OTC Antihistamines Include:- Cetirizine hydrochloride
- Loratadine
- Desloratadine
- Ebastine
- Fexofenadine
- Levocetirizine dihydrochloride
For more information on these treatments please contact your healthcare professional.
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