Allergy test: Skin Prick Tests

Allergic symptoms can be caused by different immunological mechanisms. The majority of allergic diseases are caused by either the Type I (or immediate-type) hypersensitivity response, or the Type IV (or delayed-type) hypersensitivity response. The type of tests needed to diagnose allergy depends on the type of allergic reaction being investigated.

Immediate-type hypersensitivity reactions are caused by antibodies called IgE produced by the immune system against allergens such as pollens, house dust mites, mold spores, animal dander, insect venom, food or drugs. When you are exposed to these allergens, the IgE attached to allergy cells called mast cells binds to the allergens and trigger the mast cells to release chemical mediators such as histamine. This leads to swelling, itching, redness, congestion and airway constriction within a matter of minutes.
IgE antibodies are involved in causing nasal and ocular allergies, asthma, insect sting allergies and some types of food and drug allergies.
Skin prick tests involve the introduction of a tiny amount of allergens into the surface layer of the skin, where there is a rich source of mast cells. A small swelling surrounded by redness will appear after 15 minutes if there is sensitivity to the allergens. The video above shows how this is done.

Skin prick tests are quick, safe and accurate. A large variety of allergenic extracts are commercially available for testing. However, the skin must be in good condition and the patient must not have taken antihistamines beforehand. Patients with active dermatitis or urticaria (hives) should not be tested because increased skin sensitivity might result in false positive results. 


Reference information:  www.allergy.hk

The information aims to provide educational purpose only. Anyone reading it should consult physician before considering treatment and should not rely on the information above.

Tips to Remember: Food Allergy

If you have a food allergy, your immune system overreacts to a food. This is caused by an antibody called IgE (Immunoglobulin E), which is found in people with allergies. Food allergy is more likely to develop in someone who has family members with allergies. Symptoms may occur after you consume even a tiny amount of the food.

Most allergens can cause reactions even after they are cooked or have undergone digestion in the intestines. There are some exceptions. For example, some allergens (usually fruits and vegetables) cause allergic reactions only if eaten in their raw form. Symptoms are usually limited to the mouth and throat.

The most common food allergens are the proteins in cow's milk, eggs, peanuts, wheat, soy, fish, shellfish and tree nuts.

In some food groups, especially tree nuts and seafood, an allergy to one member of a food family may result in the person being allergic to other members of the same group. This is known as cross-reactivity.

Cross-reactivity is not as common with foods from animal groups. For example, people allergic to cow's milk can usually eat beef, and patients allergic to eggs can usually eat chicken.

With shellfish, crustaceans (shrimp, crab and lobster) are most likely to cause an allergic reaction. Molluscan shellfish (clams, oysters, scallops, mussels, abalone, etc.) can cause allergic reactions, but reactions to these shellfish are less common. Occasionally, people are allergic to both types of shellfish.

Reference information: www.aaaai.org

The information aims to provide educational purpose only. Anyone reading it should consult physician before considering treatment and should not rely on the information above.

What is Allergic rhinitis?

Allergic rhinitis is caused by inflammation of the lining of the nose due to exposure to allergens. Symptoms include sneezing, itching, clear nasal discharge, post-nasal drip and congestion. Many patients with allergic rhinitis also suffer from allergy symptoms in their eyes. Allergic rhinitis is most commonly caused by allergy to house dust mites, animal dander, cockroaches, mold spores and pollens. Environmental and industrial chemicals can also cause allergic rhinitis.

Allergic rhinitis can cause significant morbidity, especially in children. Nasal congestion often leads to poor quality sleep or even sleep apnea, and results in chronic tiredness, hyperactivity and learning difficulty. Chronic mouth breathing can affect the normal development of the teeth and facial structures. Chronic post-nasal drip can lead to cough and hoarsness, and chronic congestion can cause sinus and middle ear infections. Allergic rhinitis is an important risk factor for the development of asthma in young children.

Not all cases of rhinitis are caused by allergies. Other common causes include vasomotor rhinitis, infection and medications. In order to diagnose allergic rhinitis, patients should undergo allergy testing, preferably with skin tests. The test should include all potential allergens in the patient’s outdoor, home and work environment.

Treatment of allergic rhinitis should first and foremost include avoidance of the relevant allergens. This will involve modifying the environment at home and at work. Nasal steroid spray is the most effective medication for the prevention of rhinitis symptoms, whereas acute symptoms should be treated with oral antihistamines. Long-term use of over-the-counter decongestant sprays should be avoided. For long-term management of moderate to severe allergic rhinitis, especially if the patient fails to adequately respond to allergen avoidance and medications, patients should consider undergoing desensitization treatment to induce tolerance to the relevant allergens.

Reference information:  www.allergy.hk

The information aims to provide educational purpose only. Anyone reading it should consult physician before considering treatment and should not rely on the information above.

What is allergy?

An allergic reaction occurs when our immune system reacts to otherwise harmless substances from outside our body. Our immune system has an important role in protecting us from infections. It normally recognizes bacteria, viruses and fungi by reacting to their proteins (antigens), but only under circumstances that present danger to our body such as tissue damage. In the absence of such “danger signals”, foreign proteins are usually recognized as harmless and are tolerated. This process of immune tolerance occurs the first time our immune system comes in contact with these foreign proteins, such as when an infant ingests milk formula or breathes in pollens for the first time. However, if immune tolerance to a particular antigen fails to develop or is lost, the individual then becomes sensitized to this antigen and develops antibodies and specific T cells against it. An antigen that causes allergic sensitization is called an allergen. When the individual is exposed to this allergen again, an allergic reaction occurs.

Allergic symptoms can be caused by different immunological mechanisms. The majority of allergic diseases are caused by either the Type I (or immediate-type) hypersensitivity response, or the Type IV (or delayed-type) hypersensitivity response.

Immediate-type hypersensitivity reactions are caused by antibodies called IgE produced by the immune system against allergens such as pollens, house dust mites, mold spores, animal dander, insect venom, food or drugs. When the patient is exposed to these allergens, the IgE attached to allergy cells called mast cells binds to the allergens and trigger the mast cells to release chemical mediators such as histamine. This leads to swelling, itching, redness, congestion and airway constriction within a matter of minutes. Mast cells are mostly found in the skin, respiratory tract and gastrointestinal tract. IgE antibodies are involved in causing nasal and ocular allergy, asthma, insect sting allergy and some types of food allergy and drug allergy.

Delayed-type hypersensitivity reactions are caused by a type of immune cells called T cells. Each T cell specifically recognizes one allergen, and when it is exposed to this allergen, it becomes active and produces chemical mediators that cause inflammation. This type of reaction usually occurs 24 to 72 hours after allergen exposure, and tends to become chronic. Certain types of food and drug allergy, contact dermatitis and atopic dermatitis are caused by this type of reaction.

Reference information:  http://www.allergy.hk

The information aims to provide educational purpose only. Anyone reading it should consult physician before considering treatment and should not rely on the information above.