What is an Allergy? Allergic Reaction, Immune Hypersensitivity
An allergy is an overactive immune response which is triggered when the body is exposed to some stimulus. This causes inflammation at the site of exposure or in other parts of the body and causes a range of symptoms, some of which can be life threatening. In most cases however, an allergy is not deadly but can cause severe discomfort for a short period or over a long duration of time.
How does the immune system react in an allergy?
The immune system is made up of cells and chemicals that protect the body from foreign invaders like a virus, bacteria or fungus. The immune activity is carefully coordinated by a number of factors to effectively identify the invader and destroy or isolate it as quickly as possible. However in an allergic reaction, the immune system gets activated but for the wrong reasons. The now active immune system has to act on something and often it targets the body’s tissues.
There are different types of allergic reactions but the process is similar. The body forms antibodies against the allergen (antigen) which are in abundance in the circulation and attached to different types of immune cells particularly the mast cells. When a person is exposed to the allergen again, these antibodies bind with the antigen and activate the immune cell. A rush of chemicals like histamine, bradykinin and other vasoactive substances are released which causes localized inflammation.
What causes an allergic reaction?
An allergy may start up on its own or may be linked to a family history of allergies. Certain drugs and substances can also trigger an allergic reaction. The actual reaction is caused by the immune system but it is triggered by different stimuli, either inhaled (from the air) or ingested (in food or drink). These stimuli are called allergens. Individual allergies may react to different allergens but there are the common ones that are known to be the main culprits.
Common Inhaled Allergens
- Pollen – tree, grass, plant.
- House dust mite.
- Animal hair (dander).
Common Ingested Allergens
- Milk and dairy products.
- Egg yolk.
What are the symptoms of an allergic reaction?
Signs and Symptoms of an Allergy
The signs and symptoms depend on the area that is most affected. In the three most common allergic conditions – asthma, eczema and hay fever – the same allergic reaction affects the air passages, skin and nasal passages respectively. This causes different signs and symptoms. The common symptoms of an allergy include :
- Itchy, red eyes.
- Itchy skin.
- Red skin rash.
- Mucus production and/or discharge.
- Swelling of the eyelids, lip or tongue.
How is an allergic reaction treated?
The main treatment for an allergy is through the use of antihistamine drugs. These drugs prevent the immune cells from releasing the chemical, histamine, which intensifies the allergy symptoms. This does not entirely stop the allergic reaction but rather limits the extent of the signs and symptoms. In long term allergies or severe acute allergic reactions, corticosteroids may also be used.