How Does an Allergic Reaction Happen?

When you are allergic to a certain type of allergen, you will experience an allergic reaction every time you come into contact with it.

There are two most common types of allergic reactions: those that are caused by antibodies and those that are caused by cells.

What is anaphylactic shock (Anaphylaxis)?

Anaphylactic shock is a severe allergic reaction that can have life-threatening issues. A severe allergic reaction can cause anaphylactic shock. The onset time varies from seconds to minutes or even hours after being exposed to the allergen, resulting in a rapid drop of blood pressure, accompanied by a feeling of dizziness, and even to the extent of unconsciousness and breathing difficulties.

Causes of anaphylactic shock

The most common allergens are food and insect venom (wasps).

Common food allergens, include:

  • Peanuts
  • Nuts
  • Fish and Shellfish
  • Fruits
  • Dairy products such as milk and eggs

The following substances can also cause anaphylactic shock:

  • Insect venom, wasp and bee bites are particularly common. In addition, being bitten by wasps and bumblebees may also trigger systemic allergies, but the chance is minimal.
  • Medications – usually antibiotics (eg Penicillin), Aspirin, NSAIDs (eg ibuprofen)
  • Latex
Photos, 2021 Photos, eczema photo 濕疹 picture

Allergic reaction caused by antibodies

The body's immune system produces an antibody called immunoglobulin E (or IgE) that specifically targets allergens. When the immune system produces antibodies, it will enter various systems in the body through the blood, such as the skin, trachea, and stomach. These sites contain mast cells, specifically subcutaneous, and there are IgE receptors on the surface of mast cells, which bind to IgE in the blood. Mast cell activation is triggered when an allergen comes into contact with IgE antibodies on the surface of mast cells. The active mast cells will release some inflammatory factors (such as histamine, leukotriene, etc.), causing the patient to have allergic reactions, such as vascular leakage, vascular dilatation, itching, tracheal constriction and so on. This reaction can take place in a short period of time, such as minutes to hour. Nasal allergies, asthma, urticaria, rubella, acute food allergies, drug allergies, insect allergies, etc. are all caused by type 1 allergic reactions.

Allergic reactions caused by cells

T cells of the immune system are sensitive to certain allergens, and when T cells are exposed to such allergens again, they release factors that cause an inflammatory response. A delayed allergic reaction usually occurs within 24 to 48 hours of exposure. Delayed allergic reactions can cause skin eczema, contact skin sensitivity, or food-induced gastrointestinal sensitivity.


Things to take note of for people with severe allergies:

  • Know what can cause allergic reactions and avoid exposure to allergens
  • Recognize the symptoms
  • Carry Adrenalinewherever you go, make sure you have enough and it is not expired
  • Learn how to consume or apply the medicine
  • Talk to family, friends, and colleagues about the symptoms of anaphylaxis and how to treat it with medication
  • Adrenalineis the drug of choice for the treatment of systemic allergies. Because it works fast, it can improve the condition immediately
  • Immediately after injecting Adrenalineinto the thigh, blood vessels will constrict, preventing the swelling of face and lips, relaxing the lungs and making breathing easier. In addition, adrenaline stimulates the heart and increases blood pressure.
  • The sooner the drug is injected, the better it is, and the patient should seek medical attention as soon as possible. If symptoms do not improve after 5 to 15 minutes or if symptoms reappear, the patient should prepare for a second injection.

Allergy Test

Each allergy is caused by a different immune mechanism. The type of test to be taken depends on the type of immune response.

Allergy Drug

The same goes for taking allergy medication. It is very important to take note that different allergy mechanisms utilise different treatments. Failure to do so can lead to errors in diagnosis or treatment.

Epinephrine Pen

An easy-to-use epinephrine pen. Allergy patients should carry it with them, even if a systemic allergic reaction occurs, it can be treated in time. Injecting epinephrine as early as possible at the onset of an illness can help reduce the risk of complications. Epinephrine injections work quickly and allergy symptoms subside quickly. (More)

Desensitisation Immunotherapy

Immunotherapy is currently the only cure for allergies, targeting the cause of the allergy to desensitise it. Desensitisation immunotherapy (sublingual/injection) contains a specific amount of allergens to help patients gradually build up the immune system. After a period of immunotherapy, when the patient is being exposed to the same allergen again, the allergic reaction will be greatly subsided. In other countries, especially in Europe, desensitisation therapy is becoming more common.