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Related terms
Author information
Types of allergic reactions
Common triggers

Related Terms
  • Allergen, allergic, allergic reaction, allergic response, allergy, allergy shots, anaphylactic reaction, anaphylaxis, animal dander, antibodies, antibody, antihistamines, dander, decongestants, dust, dust mites, histamine, hives, hypersensitivity, immune, immune defense system, Ig, IgE, immune-mediated, immune response, immune system, immunoglobulin, immunoglobulin E, immunotherapy, inflammation, latex, molds, leukotriene inhibitors, pet dander, pollen, radioallergosorbent test, RAST, sensitized, sensitization, skin test, trigger, white blood cells.

  • An allergy, or hypersensitivity reaction, occurs when the body's immune system overreacts to a substance that is normally harmless (allergen), such as mold, pollen, animal dander or dust mites. The white blood cells of an allergic individual produce an antibody called immunoglobulin E (IgE), which attaches to the allergen. This triggers the release of histamine and other inflammatory chemicals that cause allergic symptoms, such as runny nose, watery eyes and hives.
  • If the allergen is airborne, the allergic reaction will primarily affect the eyes, nose and lungs. If the allergen is ingested, the allergic reaction will primarily affect the mouth, stomach and intestines. If enough inflammatory chemicals are released, a reaction such as hives or rash could occur throughout the body. The most severe allergic reaction, known as anaphylaxis, can lead to low blood pressure, breathing difficulties, shock, and loss of consciousness, all of which can be fatal.
  • Allergies are extremely common, affecting more than 20% of Americans. The most common allergy triggers include pollen, dust mites, molds, animal dander, latex, foods and insect venom.
  • Allergy treatment depends on the type of allergy and severity of symptoms. Commonly used allergy medications include antihistamines, nasal sprays, decongestants, leukotriene inhibitors and allergen immunotherapy (allergy shots).

Author information
  • This information has been edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (

  1. American Academy of Allergy Asthma & Immunology. .
  2. Asthma and Allergy Foundation of America. Rhinitis and Sinusitis. .
  3. Moffitt JE, Golden DB, Reisman RE, et al. Stinging insect hypersensitivity: a practice parameter update. J Allergy Clin Immunol. 2004 Oct;114(4):869-86.
  4. National Institute of Allergy and Infectious Diseases. .
  5. Natural Standard: The Authority on Integrative Medicine. .
  6. Neugut AI, Ghatak AT, Miller RL. Anaphylaxis in the United States: an investigation into its epidemiology. Arch Intern Med. 2001 Jan 8;161(1):15-21.
  7. The Cleveland Clinic Health Information Center. Allergy Overview. .

  • Most allergies are inherited, which means they are passed on to children by their parents. Although people inherit a tendency to be allergic, they may not inherit an allergy to the same allergen. When one parent is allergic, their child has a 50% chance of having allergies. That risk jumps to 75% if both parents have allergies.
  • Typically, an allergic response is not triggered the first time the body encounters the allergen. The first, or several times after the body is exposed to an allergen, the immune system becomes sensitized and prepares to react to the next encounter with the allergen. Once sensitized, the immune system can quickly detect the drug in the body and produce immunoglobulin E (IgE). These antibodies trigger the release of chemical mediators, including histamine, which may cause allergic symptoms up to and including anaphylaxis.
  • Common allergy triggers include pollen, dust mites, molds, animal dander, latex, foods and insect venom.

  • Common allergy symptoms include runny nose, tearing eyes, burning or itching eyes, red or swollen eyes, coughing, wheezing, difficulty breathing, hives, skin rash, stomach cramps, vomiting, diarrhea, headache and itchy nose, postnasal drip, impaired smell, as well as itchy mouth, throat or skin.

  • General: Allergy treatment depends on the type of allergy and severity of symptoms. Commonly used allergy medications include antihistamines, nasal sprays, decongestants, leukotriene inhibitors and immunotherapy (allergy shots).
  • Short-acting antihistamines: Short-acting antihistamines like diphenhydramine (Benadryl®) have been used to relieve mild to moderate allergy symptoms. Most short-acting antihistamines are available over-the-counter. These medications often cause drowsiness, and they have shown to blunt learning in children (even in the absence of drowsiness). However, loratadine (Claritin®), an over-the-counter medication, does not cause drowsiness or affect learning in children. Patients should consult their healthcare providers to determine whether these medications are safe for children.
  • Longer-acting antihistamines: Longer-acting antihistamines like fexofenadine (Allegra®) or cetirizine (Zyrtec®) are available by prescription for mild to moderate allergy symptoms. They cause less drowsiness than short-acting antihistamines, and they are equally effective. These medications do not usually interfere with learning. Patients should consult their healthcare providers to determine whether these medications are safe for children.
  • Nasal corticosteroid sprays: Nasal corticosteroid sprays can effectively relieve allergy symptoms in patients who are not responding to antihistamines. Commonly prescribed corticosteroid sprays include fluticasone (Flonase®), mometasone (Nasonex®) and triamcinolone (Nasacort AQ®).
  • Decongestants: Decongestants may help relieve symptoms such as nasal congestion (stuffy nose). These drugs shrink the tissues and blood vessels in the eyes and nose that swell in response to contact with an allergen. Nasal decongestant sprays like oxymetazoline (Afrin®) should not be used more than twice daily for three consecutive days because rebound nasal congestion may result. Decongestants in pill form do not cause this effect.
  • Cromolyn sodium: Cromolyn sodium is available as a nasal spray (Nasalcrom®) for treating hay fever. Eye drop versions of cromolyn sodium are also available for itchy, bloodshot eyes.
  • Leukotriene inhibitors: Leukotriene inhibitors like montelukast (Singulair®) have been used to control allergic asthma and to help relieve seasonal allergy symptoms.
  • Immunotherapy (allergy shots): Allergen immunotherapy, also known as allergy shots, is often used to treat patients who suffer from severe allergies, or for those who experience allergy symptoms more than three months a year. Allergen immunotherapy involves injecting increasing amounts of an allergen to a patient over several months.

Types of allergic reactions
  • Allergic reactions can be classified into four immunopathologic categories using various classification systems. The Gell and Coombs allergic classification system is based on the immune system's response to the allergen, not on the severity of the reaction.
  • Type I: Type I allergic reactions involve immunoglobulin E (IgE), which is specific for a particular drug, antigen or other allergen that triggers the allergic reaction. The allergen binds to the immunoglobulin on specific immune cells called basophils and mast cells. This binding results in the release of chemicals that cause inflammation in the body (such as histamine, serotonin, proteases, bradykinin generating factor, chemotactic factors from immune cells, leukotrienes, prostaglandins and thromboxanes) within 30 minutes of exposure. These chemical mediators cause allergy symptoms, such as urticaria (hives), runny nose, watery eyes, sneezing, wheezing and itching. This type of allergic reaction is often seen with penicillin, latex, blood products and vaccines.
  • Type II: This classification is called a cytotoxic reaction because it involves the destruction of the host cells. An antigen associated with a specific cell initiates cytolysis (breakdown of the cell) by an antigen-specific antibody, such as immunoglobulin G (IgG) or immunoglobulin M (IgM). This reaction often involves blood elements, such as red blood cells, white blood cells or platelets. It often occurs within five to 12 hours of exposure to the allergen, which may include penicillin, quinidine, phenylbutazone, thiouracils, sulfonamides or methyldopa.
  • Type III: This category involves the formation of an antigen-antibody immune complex, which deposits on blood vessel walls and activates cell components called complements. This causes a serum sickness-like syndrome, involving fever, swelling, skin rash and enlarged lymph nodes, in about three to eight hours. It may be caused by a variety of allergens, including penicillins, sulfonamides, intravenous (IV) contrast media and hydantoins.
  • Type IV: This classification involves delayed cell-mediated reactions. Antigens on the allergen release inflammatory mediators within 24 to 48 hours of exposure. This type of reaction is seen with graft rejection, latex, contact dermatitis and tuberculin reaction.

Common triggers
  • Pollen: Each spring, summer and fall, plants release tiny particles called pollen into the air in order to reproduce. Pollen from plants, such as ragweed, can trigger allergy symptoms.
  • Dust: Dust mites are microscopic organisms that live in dust and in the fibers of household objects like pillows, mattresses and carpets. Dust mites prefer warm, humid areas. Household dust is a combination of potentially allergenic materials, including fibers from different fabrics, animal dander, bacteria, mold, fungus spores, food particles, bits of plants or other allergens.
  • Molds: Molds are parasitic, microscopic fungi (like Penicillium) that have spores that float in the air like pollen. Mold is a common trigger for allergies, and it is usually found in damp areas, such as the basement or bathroom, as well as outside in grass, leaf piles, hay or mulch. In some people, symptoms of mold allergy may be triggered or worsened after eating certain foods, such as cheese processed with fungi. Mold spores peak during hot, humid weather.
  • Animal dander: Animals secrete oily fluids from their skin, which contain allergens. These fluids collect on fur, feathers and other surfaces inside the home. Proteins in the animal's saliva also cause allergic reactions. The allergens are capable of triggering reactions for several months. Allergies to animals can take two or more years to develop, and symptoms may not subside until months after discontinuing contact with the animal.
  • Latex: Latex, a substance found in products like rubber gloves or condoms, can also trigger allergic reactions in sensitive people. A component of the latex substance itself is an allergen. In addition, the latex glove powder residue is an airborne allergen that causes upper airway allergic reactions in some people. Latex reactions may cause a potentially life-threatening allergic reaction called anaphylaxis. According to the American Academy of Allergy Asthma & Immunology (AAAAI) about 220 cases of anaphylaxis and three deaths per year are attributed to latex allergies.
  • Foods: Food allergens are those parts of foods, usually proteins, which lead to allergic reactions. Most allergens can still cause allergic reactions even after they are cooked or have been digested. However, some allergens (usually from fruit and vegetables) only cause allergic reaction if eaten raw. These reactions are usually limited to the mouth and throat. According to the AAAAI, six foods, including milk, peanuts, soy, eggs, wheat and tree nuts (like pecans and walnuts), cause 90% of food allergies in children. Children usually outgrow allergies to milk, eggs and soy, but peanut, tree nut, fish and shellfish allergies continue throughout adulthood.
  • Insect venom: The honeybee, yellowjacket, paper wasp, white-faced hornet (bald-faced hornet) and fire ant are among the most common insects that trigger insect sting or bite allergies. Since the stinger is a modified egg-laying apparatus, only females can sting.

Copyright © 2011 Natural Standard (

The information in this monograph is intended for informational purposes only, and is meant to help users better understand health concerns. Information is based on review of scientific research data, historical practice patterns, and clinical experience. This information should not be interpreted as specific medical advice. Users should consult with a qualified healthcare provider for specific questions regarding therapies, diagnosis and/or health conditions, prior to making therapeutic decisions.

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