Allergic Reaction Overview & Causes

Allergic Reaction Overview

An allergic reaction is the body's way of responding to an "invader." When the body senses a foreign substance, called an antigen, the immune system is triggered. The immune system normally protects the body from harmful agents such as bacteria and toxins. Its overreaction to a harmless substance (an allergen) is called a hypersensitivity reaction, or an allergic reaction.

• Anything can be an allergen. Dust, pollen, plants, medications, (such asibuprofen, sulfa drugs like sulfamethoxazole and trimethoprim [Bactrim],codeine, amoxicillin [Amoxil, Amoxil Pediatric Drops, Moxatag, Trimox]), foods (common food allergies include shrimp and other shellfish, peanuts),insect bites (such as from mosquitos or bees), animal dander, viruses, or bacteria are examples of allergens.
• Reactions may occur in one spot, such as a small localized skin rash, itchy eyes, face bumps, or all over, as in a whole body rash such as hives (urticaria).
• A reaction may include one or several symptoms.

Most allergic reactions are minor, such as a rash from poison ivy, mosquito or other bug bites, or sneezing from hay fever. The type of reaction depends on the person's immune system response, which is sometimes unpredictable.

In rare cases, an allergic reaction can be life-threatening (known as anaphylaxis). Each year in the United States, it is estimated that there are 150,000 cases of anaphylaxis. Up to 500-1,000 fatalities due to anaphylaxis occur each year.

Allergies are very common. The Asthma and Allergy Foundation (AAFA) states allergies affect 50 million Americans, is the fifth leading chronic disease in the U.S., and the third leading among children. More than 40 million people have indoor/outdoor allergies as their primary allergy. More than 17 million people visit their doctor for allergies annually, and food allergies account for 50,000 visits to the emergency room annually.

Allergic Reaction Causes

Almost anything can trigger an allergic reaction.

• The body's immune system involves the white blood cells, which produce antibodies.
• When the body is exposed to an antigen, 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 help destroy substances that cause disease and sickness. In allergic reactions, the antibody is called immunoglobulin E or IgE.
• This antibody promotes production and release of chemicals and hormones called "mediators."
• 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.
• Histamine is one of the better-known mediators produced by the body.
• If the release of the mediators is sudden or extensive, the allergic reaction may also be sudden and severe, and anaphylaxis may occur.
• Allergic reactions are unique for each person. Reaction time to allergens can vary widely. Some people will have an allergic reaction immediately, for others it will take time to develop.

• Most people are aware of their particular allergy triggers and reactions.
• Certain foods such as peanuts, strawberries, shellfish, shrimp, dairy, and wheat.
• Babies can also have food allergies. There are more than 160 allergenic foods. Common foods that can cause allergic reactions in babies include milk, eggs, nuts, and soy. Talk to your pediatrician if you are concerned about food allergies in your baby.
• Food intolerance is not the same as food allergies. Allergies are an immune system response, while food intolerance is a digestive system response in which a person is unable to properly digest or break down a particular food.
• Vaccines and medications (antibiotics like penicillin, amoxicillin, aspirin, ibuprofen, iodine), general anesthesia and local anesthetics, latex rubber (such as in gloves or condoms), dust, pollen, mold, animal dander, and poison ivy are well-known allergens. Other known allergens can include detergents, hair dyes, and the ink in tattoos.
• Bee stings, fire ant stings, penicillin, and peanuts are known for causing dramatic reactions that can be serious and involve the whole body.
• Minor injuries, hot or cold temperatures, exercise, stress, or emotions may trigger allergic reactions.
• Often, the specific allergen cannot be identified unless you have had a similar reaction in the past.
• Allergies and the tendency to have allergic reactions run in some families.
• Many people who have one trigger tend to have other triggers as well.
• People with certain medical conditions are more likely to have allergic reactions:
• severe allergic reaction in the past
• asthma
• lung conditions that affect breathing, such as chronic obstructive pulmonary disease (COPD)
• nasal polyps
• frequent infections of the nasal sinuses, ears, or respiratory tract
• sensitive skin, especially sufferers of eczema.

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