Skip to content

Allergies Health Center

Understanding Allergies -- the Basics

Font Size
A
A
A

What Are Allergies?

The term allergy applies to an abnormal reaction by your immune system to a substance that is usually not harmful. Allergies come in a variety of forms and vary in severity from mildly bothersome to life-threatening. An estimated one-fifth of the Western Hemisphere's population suffers from allergies.

At this time, researchers are not sure what factors contribute to the development of allergies, but heredity seems to play a role. Allergies may flare up and subside throughout your life. A normally functioning immune system protects the body from foreign substances -- known as antigens -- by producing antibodies and other chemicals to fight against them. Usually the immune system ignores harmless substances, such as food, and fights only dangerous ones, such as bacteria. A person develops an allergic reaction when the immune system inappropriately reacts and releases chemicals like histamine to attack a harmless protein as if it were a threat. Histamine produces many of the symptoms associated with allergies. The hundreds of proteins that may trigger allergic reactions range from pollen to pet dander to penicillin.

Understanding Allergies

Find out more about allergies:

Basics

Symptoms

Treatment

Prevention

Most allergic reactions are not serious, but some, such as anaphylaxis, can result in an inability to breathe or a severe drop in blood pressure and can be fatal. 

Allergies can't be cured outright, but a variety of treatments are available to relieve the symptoms. If you have a severe allergy, it is vital that you visit a doctor -- ideally a board certified allergist -- and get immediate treatment. A severe allergic (anaphylactic) reaction can be life threatening and requires emergency treatment.

 

Types of Allergies

Allergic (or atopic) conditions come in many distinct forms and are typically grouped in general categories according to the types of reaction or the parts of the body they affect. Histamine and the protein antibody IgE are usually involved in immediate reactions; delayed reactions are typically identified as cell-mediated, primarily driven by immune cells.

Allergic skin conditions: The cause of eczema -- also called atopic dermatitis -- is unknown. But it's thought that it's potentially caused by a combination of things including direct skin exposures to antigens, hereditary factors, impaired immune function, and disruption of the skin’s barrier function. Hives, or urticaria, is a rash consisting of an eruption of itchy, swollen, reddened lesions that can last for minutes or days. Hives are not uncommon, affecting an estimated one in five people at some time in their lives. Angioedema is characterized by a deeper swelling in body tissues, typically around the eyes and lips, and sometimes of the hands, feet, or other parts of the body as well. Both hives and angioedema may stem from the body's adverse reaction to certain foods, pollen, animal dander, drugs, insect stings, cold, heat, light, or even emotional stress. Often, however, the cause may not be identified. Both of these reactions can occur in isolated cases and may not necessarily be an indicator of anaphylaxis. Chronic cases or cases of hives or angioedema complicated by other symptoms should be discussed with your physician.

1 | 2 | 3

Today on WebMD

man blowing nose
Make these tweaks to your diet, home, and lifestyle.
Allergy capsule
Breathe easier with these products.
 
cat on couch
Live in harmony with your cat or dog.
Woman sneezing with tissue in meadow
Which ones affect you?
 

blowing nose
Article
woman with sore throat
Article
 
lone star tick
Slideshow
Woman blowing nose
Slideshow
 

Send yourself a link to download the app.

Loading ...

Please wait...

This feature is temporarily unavailable. Please try again later.

Thanks!

Now check your email account on your mobile phone to download your new app.

cat lying on shelf
Article
Allergy prick test
VIDEO
 
Man sneezing into tissue
Assessment
Woman holding feather duster up to face, twitching
Quiz