The immune system is the body’s organized defense mechanism against foreign invaders, particularly infections. Its job is to recognize and react to these foreign substances, which are called antigens. Antigens are substances that are capable of causing the production of antibodies. Antigens may or may not lead to an allergic reaction. Allergens are certain antigens that cause an allergic reaction and the production of IgE.

The aim of the immune system is to mobilize its forces at the site of invasion and destroy the enemy. One of the ways it does this is to create protective proteins called antibodies that are specifically targeted against particular foreign substances. These antibodies, or immunoglobulins (IgG, IgM, IgA, IgD), are protective and help destroy a foreign particle by attaching to its surface, thereby making it easier for other immune cells to destroy it. The allergic person however, develops a specific type of antibody called immunoglobulin E, or IgE, in response to certain normally harmless foreign substances. To summarize, immunoglobulins are a group of protein molecules that act as antibodies. There are five different types; IgA, IgM, IgG, IgD, and IgE. IgE is the allergy antibody.

The Immune System

Foreign Substance

(cat dander, pollen, virus, bacteria)
Normal Immune Response

IgM, IgG, IgA, IgD and various immune cells respond to attack.
Exaggerated Immune Response

IgE is overproduced in response to cat dander, pollens, and other harmless allergens.
Foreign substance is eliminated.
Subsequent exposure results in an allergic reaction.
Non-Allergic Individual
Allergic Individual


What is an Allergy ?

Allergies are an abnormal response of the immune system. People who have allergies have an immune system that reacts to a usually harmless substance in the environment. This substance (pollen, mold, and animal dander, for example) is called an allergen.

What Are the Symptoms of an Allergic Reaction?

Common symptoms of an allergic reaction to inhaled or skin allergens include:
Itchy, watery eyes
Itchy, runny nose
Feeling tired or ill
Hives (a rash with raised red patches)
Other exposures can cause different allergic reactions:
Food allergies. An allergic reaction to food allergens can also cause stomach cramps, vomiting, or diarrhea.
Insect stings. The allergic reaction to a sting from a bee or other insect causes local swelling, redness, and pain.

The severity of an allergic reaction’s symptoms can vary widely:
Mild symptoms may be almost unnoticeable, just making you feel a little “off.”
Moderate symptoms can make you feel ill, as if you’ve got a cold or even the flu.
Severe allergic reactions are extremely uncomfortable, even incapacitating.

Most symptoms of an allergic reaction go away shortly after the exposure stops.
The most severe allergic reaction is called anaphylaxis. In anaphylaxis, allergens cause a whole-body allergic reaction that can include:
Hives and itching all over (not just in the exposed area)
Wheezing or shortness of breath
Hoarseness or tightness in the throat
Tingling in the hands, feet, lips, or scalp
Anaphylaxis is life-threatening and requires immediate medical attention. Symptoms can progress rapidly, so head for the emergency room if there’s any suspicion of anaphylaxis.

Allergic Reaction Causes:

Many substances can trigger an allergic reaction.

1. The body’s immune system has a patrol of white blood cells, which produce antibodies.
When the body is exposed to an antigen — a substance that causes the immune system to make antibodies against it — a complex set of reactions begins.
The white blood cells produce an antibody specific to that antigen. This is called “sensitization.”
The job of the antibodies is to detect and destroy substances that cause disease and sickness. In allergic reactions, the antibody is called immunoglobulin E, or IgE.
2. This antibody promotes production and release of chemicals and hormones called “mediators.”
Histamine is one well-known mediator.
Mediators have effects on local tissue and organs in addition to activating more white blood cell defenders. It is these effects that cause the symptoms of the reaction.
If the release of the mediators is sudden or extensive, the allergic reaction may also be sudden and severe.
3. Your allergic reactions are unique to you. For example, your body may have learned to be allergic to poison ivy from repeated exposure.
4. Most people are aware of their particular allergy triggers and reactions.
Certain foods, medications, latex, aspirin, shellfish, dust, pollen, mold, animal dander, and poison ivy are famous allergens.
Bee stings, fire ant stings, penicillin, and peanuts are known for causing dramatic reactions in some people that can be serious and involve the whole body.
Minor injuries, hot or cold temperatures, exercise, or even emotions may be triggers.
Often, the specific allergen cannot be identified unless you have had a similar reaction in the past.
5. Allergies and the tendency to have allergic reactions run in some families. You may have allergies even if they do not run in your family.
6. Many people who have one trigger tend to have other triggers as well.
7. People with certain medical conditions are more likely to have allergic reactions.
Severe allergic reaction in the past
Lung conditions that affect breathing, such as chronic obstructive pulmonary disease (COPD)
Nasal polyps
Sensitive skin

Allergy Types :

1. Food Allergies
Food allergies or food intolerances affect nearly everyone at some point. People often have an unpleasant reaction to something they ate and wonder if they have a food allergy.
Milk Allergy
Egg Allergy
Wheat Allergy
Nut (Peanut) Allergy
Fish Allergy
Soy Allergy
2. Seasonal Allergies
3. Pet Allergies
4. Other Allergies
Hay Fever
Hay fever is an immune disorder characterized by an allergic response to pollen grains and other substances. Also known as allergic rhinitis, there are two types: seasonal, which occurs only during the time of year in which certain plants pollinate, and perennial, which occurs all year round.

Allergic Conjunctivitis (Pink Eye)
Pink eye caused by bacteria, viruses, or STDs can spread easily from person to person but is not a serious health risk if diagnosed promptly; allergic conjunctivitis is not contagious.

Hives (Urticaria)
Hives, also known as urticaria, are an outbreak of swollen, pale red bumps, patches, or welts on the skin that appear suddenly — either as a result of allergies, or for other reasons.

Allergies to Insect Stings (Bee Stings)
Bee, wasp, yellow jacket, hornet, or fire ant stings are the insect stings that most often trigger allergies. However, most people are not allergic to insect stings and may mistake a normal sting reaction for an allergic reaction.

Mold Allergy
People with mold allergies, however, may have a reaction if exposed to too much of the fungus.

Pollen Allergies
For most people, changing seasons can mean misery.

Sun Reactions of the Skin
Most people’s skin will burn if there is enough exposure to ultraviolet radiation. However, some people burn particularly easily or develop exaggerated skin reactions to sunlight.

Aspirin Allergy (Salicylate Allergy)
Salicylates are chemicals found naturally in plants and are a major ingredient of aspirin and other pain-relieving medications. They are also found in many fruits and vegetables as well as in many common health and beauty products.

Cosmetic Allergy
Although cosmetics can help us feel more beautiful, they can cause skin irritation or allergic reactions. Certain ingredients used in cosmetics, such as fragrances and preservatives, can act as  allergens, substances that trigger an allergic reaction.

Nickel Allergy
A nickel allergy is a skin reaction that develops after exposure to nickel or items containing the metal.

Drug Allergy
Many drugs can cause adverse side effects, and certain medicines can trigger allergic reactions. In an allergic reaction, the immune system mistakenly responds to a drug by creating an immune response against it.

  Dust Allergy
Life with dust allergies — whether they’re yours or a family member’s — comes with a load of questions. For instance, might a dust allergy explain your child’s never-ending cold symptoms?

Chemical Allergy
They promise to make your skin soft, your hair shiny, and your laundry springtime fresh, but for some people the chemicals in shampoos, cosmetics, and detergents trigger allergic skin reactions.

Penicillin Allergy
A penicillin allergy is an allergic reaction that occurs when your body’s immune system overreacts to penicillin antibiotics. A penicillin allergy is an allergic reaction that occurs when your body’s immune system overreacts to penicillin antibiotics.