

Allergy Overview

Picture of an elderly man clenching his aching head

What is allergy?

Allergy is a physiological reaction caused when the immune system mistakenly identifies a normally harmless substance as damaging to the body.

Normally, the human body defends itself against harmful substances such as viruses or bacteria, but sometimes the defenses aggressively attack usually innocuous substances such as dust, mold, or pollen.

The immune system generates large amounts of the antibodies called immunoglobin E (IgE), a complex chemical weapon, to attack and destroy the supposed enemy. Each IgE antibody specifically targets a particular allergen—the substance that causes the allergy. In this disease-fighting process, inflammatory chemicals like histamines, cytokines, and leukotrienes are released or produced, and some unpleasant (and, in extreme cases, life-threatening) symptoms may be experienced by an allergy-prone person.

What are allergic reactions?

An allergic reaction may occur anywhere in the body, in the skin, eyes, lining of the stomach, nose, sinuses, throat, and lungs—places where immune system cells are located to fight off invaders that are inhaled, swallowed, or come in contact with the skin. Reactions may result in:

  • Seasonal or allergic rhinitis (nasal stuffiness, sneezing, nasal itching, nasal discharge, itching in ears or roof of mouth)
  • Allergic conjunctivitis (red, itchy, watery eyes)
  • Atopic dermatitis or eczema (red, itchy, dry skin)
  • Urticaria (hives or itchy welts)
  • Contact dermatitis (itchy rash)
  • Asthma (airway problems, such as shortness of breath, coughing, wheezing)

What causes allergic reactions?

Although hundreds of ordinary substances could trigger allergic reactions, the most common triggers—called allergens—include:

  • Pollens
  • Molds
  • Household dust, dust mites and their waste
  • Animal protein (dander, urine, oil from skin)
  • Industrial chemicals
  • Foods
  • Medicines
  • Feathers
  • Insect stings
  • Cockroaches and their waste
  • Latex

Who is affected by allergy?


There's a tendency for allergies to occur in families, although the exact genetic factors that cause it aren't yet understood. In susceptible people, factors, such as hormones, stress, smoke, perfume, or other environmental irritants, may also play a role. Often, the symptoms of allergies develop gradually over a period of time.

Allergy sufferers may become so accustomed to chronic symptoms, such as sneezing, nasal congestion, or wheezing, that they don't consider their symptoms to be unusual. Yet, with the help of an allergist, these symptoms can usually be prevented or controlled and quality of life greatly improved.

How is allergy diagnosed?

In addition to performing a clinical examination and taking a medical history, your health care provider may also use:

  • Skin test. The skin test is a method of measuring the patient's level of IgE antibodies to specific allergens. Using diluted solutions of specific allergens, the health care provider either injects the patient with the solutions, or applies them to a small scratch or puncture. Reaction appears as a small red area on the skin. Reaction to the skin test doesn't always mean that the patient is allergic to the allergen that caused the reaction.
  • Blood test. The blood test is used to measure the patient's level of IgE antibodies to specific allergens. One common blood test is called RAST (radioallergosorbent test).

What is the treatment for allergy?

Specific treatment for allergy will be determined by your health care provider based on:

  • Your age, overall health, and medical history
  • Extent of the disease
  • Your tolerance for specific medications, procedures, or therapies
  • Expectations for the course of the disease
  • Your opinion or preference

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Online Resources of Allergy & Asthma

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