Allergies occur when the immune system reacts to a foreign substance, such as foods, pollen, medication or bee venom, leading to inflammation of the skin, sinuses, airways or digestive system. The immune system incorrectly considers a particular allergen as harmful and tries to destroy it.

Allergies develop once the immune system has built up a sensitivity to the substance, resulting in sensitization. Some allergies are seasonal, which means symptoms peak during certain times of the year. Allergies may occur in the airways, gut, skin, sinuses, eyes or nasal passages.

Symptoms of Allergies

Depending on the type of allergy, individuals may experience the following symptoms:

  • Sneezing
  • Runny, stuffy nose
  • Itching of the nose, eyes, or roof of the mouth
  • Watery, red or swollen eyes
  • Stomach cramps
  • Diarrhea
  • Hives
  • Tingling in the mouth
  • Swelling of the lips, tongue, face or throat
  • Cough
  • Chest tightness
  • Wheezing
  • Shortness of breath
  • Rash
  • Itchy, red, flaky or peeling skin
  • Anaphylaxis:
    • Loss of consciousness
    • Drop in blood pressure
    • Skin rash
    • Lightheadedness
    • Severe shortness of breath
    • A rapid, weak pulse
    • Nausea and vomiting

Causes of Allergies

During an allergic reaction, allergens bind to antibodies called immunoglobulin E (IgE), which combat the substances considered harmful by the immune system. Specific types of cells then release chemicals, such as histamine, that trigger the symptoms of an allergic reaction.

Individuals may develop allergies to the following substances:

  • Airborne allergens: pollen, animal dander, mold, mildew and dust mites
  • Insect stings: from a bee or wasp
  • Medications: penicillin or penicillin-based antibiotics
  • Foods: peanuts, tree nuts, wheat, shellfish, soy, fish, eggs and milk
  • Latex or other substances that are touched
  • Other common allergens:
    • Cockroaches, caddisflies, midges and moths
    • Household chemicals
    • Metals, such as nickel, cobalt, chromium and zinc

Risk Factors

Individuals may be at greater risk of developing an allergy if they have a family history of asthma or allergies, are a child, have asthma, or have another allergic condition.

Diagnosing Allergies

Individuals experiencing symptoms of an allergy should schedule an appointment with their physician. During an initial visit, patients will be asked to explain:

  • Which symptoms they have been experiencing
  • When and how often the symptoms occur
  • Potential causes
  • Family history of allergies
  • Whether or not household members have similar symptoms

The physician may order the following tests to identify the cause of symptoms:

  • Blood test. To measure the levels of IgE antibodies to specific allergens in the immune system.
  • Skin prick test. Prick the skin with a small amount of a possible allergen to see if the skin reacts.
  • Patch test. Tape a metal disc with a small amount of a suspected allergen to the patient’s back to test for contact eczema.

Treatment Options

Individuals can reduce their risk of symptoms by avoiding the allergen. This may not always be possible, and the individual may need medical treatment. Individuals with allergies may benefit from the following treatments:

  • Antihistamines, to block the action of histamine.
  • Corticosteroids, to reduce inflammation.
  • Decongestants, to relieve a blocked nose.
  • Immunotherapy, to develop long-term tolerance.
  • Leukotriene receptor antagonists (antileukotrienes), to block chemicals that cause swelling.