What are allergies?

Dr. Leigh Vinocur, MD
Emergency Medicine Specialist

Allergies are a result of overactive immune systems reacting to relatively harmless substances, such as dust and pollen, as they were invading bacterium or viruses.

Allergies, sometimes referred to as allergic rhinitis, are a very common health problem involving an inappropriate response of our immune systems to allergens, substances that can induce allergic reactions. There are both outdoor and indoor allergens. Aside from different types of pollens and molds, allergens can include animal dander and dust mites.

Allergies can negatively impact quality of life, as well as decrease productivity in our daily jobs. Allergies can also worsen other health problems like asthma.

Allergies occur when your immune system overreacts to a substance that is exposed to your body. While the substance is usually harmless, a slight irritation to your immune system causes it to react anyway.

Allergies occur when your body has an exaggerated response to a harmless substance (like dust) that it mistakenly perceives as an invader (like a virus). The immune system reacts by releasing antibodies to attack the harmless substance, known as an allergen. Antibodies trigger the release of histamine and other chemicals in the body that cause symptoms of allergies, such as itchy eyes, runny nose, nasal congestion, itchy skin and hives.

Dr. Mehmet Oz, MD
Cardiologist (Heart Specialist)

More than one-third of Americans have allergies, but most don't have their symptoms under control. Allergies are exaggerated reactions of the immune system to substances that don't cause symptoms in most people. Those reactions can come in the form of:

  • Skin rashes (typically from chemicals)
  • Runny and stuffy noses (from dust, pollen, etc.)
  • Itchy eyes (from dust, pollen, etc.)
  • Upset stomach or intestines (from food allergies)
  • Coughing, shortness or breath, wheezing or any distress to the respiratory system (from any kind of allergen)
YOU: The Owner's Manual, Updated and Expanded Edition: An Insider's Guide to the Body that Will Make You Healthier and Younger

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YOU: The Owner's Manual, Updated and Expanded Edition: An Insider's Guide to the Body that Will Make You Healthier and Younger

Between your full-length mirror and high-school biology class, you probably think you know a lot about the human body. While it's true that we live in an age when we're as obsessed with our bodies as...
Dr. Jacob Teitelbaum
Integrative Medicine Specialist

Allergies occur when our body's immune (defense) system reacts to something harmless in our environment. Inhalation allergies like pollen can cause mild symptoms, such as red eyes, itching, hives or runny nose. Food allergies are more likely to cause a wide assortment of symptoms (fatigue, pain, nasal congestion, migraines, spastic colon, autism, and many more), and should be considered when your doctor does not know the cause of a problem. In rare cases they can be life threatening (anaphylaxis where the throat swells shut or shock can occur) as occurs in some peanut allergies. For those with the latter type, carrying an "Epi-pen" (preloaded adrenaline syringe) can be life saving.

Allergies, by definition, are a reaction to the body seeing something as "foreign." As a result, any part of your body that comes into direct contact with the environment around us or the things we breathe or ingest can cause an allergic reaction. Allergic symptoms include dry or itchy skin, hives, runny nose, or itchy, red eyes, shortness of breath, nausea, vomiting or diarrhea, or even swelling of your tongue or throat in more severe reactions.

Airborne allergies come from allergens that are carried through the air, and they're most strongly associated with the classic allergy symptoms of watery eyes, runny nose and throat coated with phlegm.

Allergies occur as a result of your immune system overreacting to a foreign substance. In an effort to protect your body, your immune system attacks foreign invaders and harmful substances. In some cases, however, your immune system mistakenly attacks a harmless substance, which produces an allergic reaction.

The skin is the body's largest organ, and normally it helps keep "good stuff" like nutrients and water in, and keeps "bad stuff" like bacteria out. Sometimes, however, certain substances may cause an abnormal immune response in the skin, either through physical contact or as a result of ingesting something. This kind of reaction is known as skin allergies, which include any kind of reaction to something that results in a rash, hives, blisters or other skin irritations. Skin allergies are affected by Langerhans' cells, which are special cells found in the epidermis (the outermost layer of skin) that are part of the skin's immune system. Normally, these cells help defend the body against infection, but sometimes they can be part of the development of skin allergies. The classification of "skin allergies" may include dermatitis (eczema), lichen planus and various types of rashes or hives.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.