What is allergy?

Allergy is the inflammatory response of our immune system towards normally harmless substances in the environment.

Hong Kong statistics on epidemiology has revealed that allergy may be a chronic disease that most people have:

• 30% of children had nasal allergy
• 7-10% of them had asthma
• 5% of them had eczema
• 5% of them had food allergy

Many people believe that only those who are not healthy will suffer from allergies, that skin allergy is contagious, and that eating a little of the wrong food will not trigger food allergy… All these are misconceptions. Allergy can bring inconvenience and frustrations; it may also lead to other complications, which can be fatal in severe cases. It is a disease that should not be overlooked.

The cause of allergic reaction

When the body comes into contact with a certain allergen, the immune system will react in a number of ways. Immune cells will produce plenty of specific Immunoglobin E(IgE) to fight against the allergen. Coming into contact with IgE and being stimulated, mast cells will release substances that cause inflammation including histamine, prostaglandin and leukotriene, which will in turn lead to allergy symptoms: rashes, redness and swelling, breathlessness, vomiting, watery eyes and a runny nose. Severe allergic response may result in a swollen airway, trigger acute asthma and difficulty breathing; blood pressure may drop rapidly and will lead to shock, which can be fatal if not treated promptly.

Common types of allergy

Nasal allergy, asthma, food allergy, skin allergy, eczema, insect bites and drug allergy.

Common allergens

Cow’s milk, egg white, peanuts, tree nuts, dust mites, pollen, wheat and barley, soy bean, insects, animal feather and hair, shrimps, prawns, crabs, fish, fresh water fish and crustaceans, seafood, and so on.

Why is there allergy?

It is not easy to identify the cause of allergy as there are many possible allergens. However, allergens occur mainly because there are changes in the environment, which may be a result of relocation, changes in diet, food source, climate or daily habits. There may not be any immediate reactions in the body. Some people may only react months or years later.  

Allergy can also be inherited. If either parent has some form of allergy, his/her children will have a higher chance for allergy.

Stress frome work or school, and anxiety can trigger allergy.

An illustration on allergic reactions

How to diagnose?

Allergy symptoms vary in intensity from one person to another and with different allergens, there may be different reactions. Learning that allergens may be the cause of a disease, a doctor will run a skin test to identify the allergen and then confirm the finding with a blood test on the level of IgE. If needed, a challenge test can be conducted in a controlled environment such as a hospital where a patient will come into contact or eat the allergen. If he/she develops symptoms as expected, his/her allergic responses are caused by that particular allergen. This test is also used to confirm whether a patient has fully recovered from the allergy.

Skin test

It does not cause any pain and is bearable even for young children. In this test a needle is used to barely penetrate the skin’s surface on the back or forearm of a patient and apply a small amount of the allergen extract, which the body will absorb.

For an allergy patient, the allergen and a certain antibody in the mast cells of the skin will react and produce naturally occurring histamine. This substance will cause the skin to develop an itchy bump that may look like a mosquito bite. A medical staff will then measure and take down the bump’s size in 15 minutes.  

Positive (histamine) and negative (saline) control tests should also be conducted; the results are used as benchmarks with which the test result will be compared for a conclusion.

The size of the bump reveals the intensity of the allergy. Apart from this, it is also important to consider the patient’s medical history and doctor’s observation when analyzing the case. The size of the bump depends on a number of factors: how concentrated the allergen extract is; whether the extract is freshly prepared; how experienced the technical personnel administering the test is; whether the patient has taken antihistamines and for how long. All these may affect the result of the test. 

If a patient says that his/her allergy will be triggered if cats are around. In this case, even if the skin test result show that he reacts less to cat hair than to indoor dust mites, this patient should be recommended to stay away from cats and avoid coming into contact with them. If this is not possible (like when visiting a friend who keep a cat), the patient may take medicines appropriate for the situation, such as allergy drugs for cats or indoor dust mites, to prevent allergy attack. For people with asthma doing the skin test, it is best to have allergens inhaled or taken by mouth. The allergy test on food allergens for adults is not effective unless it is conducted on those with severe allergic reactions to identify the intensity of their allergy towards food like peanuts. However, if cow’s milk is the allergen, this test is useful in examining whether a young child is allergic to dairy products.

The skin test can help us identify the allergic reactions towards bee and wasp venom or medicines like penicillin. It should be conducted in a specialist’s clinic. The allergy test is useful in assessing diseases caused by allergies, such as asthma, hay fever and eczema. Patients should avoid any identified allergens and this will greatly help relieve symptoms.

Major treatment options

Regarding the types of allergy, there are a number of treatments:

• Avoid any contacts with allergens

It is best to avoid or minimize contacts with allergens. Learn to avoid them in your daily life. For example, take note of the ingredients used in food; wash with hot water and change beddings and clothes frequently; do not keep pets.

• Systemic medication　

It consists of the main use of antihistamines, and topical use of low-dose steroids and anti-inflammatory drugs to reduce inflammation of the immune system.

• Topical symptom control

Examples are drugs for runny nose, vomiting and diarrhoea, brochodilators, and antibiotics.

• Allergen immunotherapy

Inject gradually increasing quantities of specific allergens under the skin to induce tolerance to the allergens and reduce allergic reactions. This treatment has certain risk factors and must be undertaken under the supervision of a doctor in a hospital or clinic.

• Rescue treatment

For severe allergic reactions, the treatment is injection of epinephrine.

A doctor will first determine the conditions of a patient, make a clinical diagnosis and decide which treatment is appropriate. Please consult your doctor for the details of different treatments.