Children's Hospital Colorado

Allergic Reactions

What is an allergic reaction?

Allergic reactions occur when the body's immune system responds to a harmless substance as if it were a toxin or a foreign invader. This overactive response can be caused by one of several different types of immune mechanisms and can involve virtually any organ or multiple organs in the body.

The parts of the body that are commonly involved in allergic reactions include the nasal passages, the eyes, the skin and the gastrointestinal tract. Anaphylaxis is the term used to refer to an allergic reaction that is life threatening and involves multiple organ systems.

What causes allergic reactions?

The timing of allergic reactions varies depending upon the immune mechanism involved in causing the reaction. Some allergic reactions occur immediately after a sensitized person is exposed to the allergen, whereas other allergic reactions take hours to days to develop. Skin testing or blood work may help to determine the cause of reaction when symptoms occur soon after exposure to the allergen, but are not always helpful when the allergic reaction occurs hours to days after exposure.

What are common allergy symptoms?

Symptoms associated with allergic disease often include itching, redness and swelling of the involved organ. When the respiratory system is involved, additional symptoms may include mucous production, nasal congestion, postnasal drip, sneezing, coughing, wheezing and difficulty breathing. Other symptoms such as gastrointestinal may include nausea, vomiting, diarrhea, poor appetite, food refusal and failure to gain or maintain weight.

A child with allergies will probably experience one or more tests in their course of diagnosis and treatment. As a parent, it is important for you to know that our doctors, nurses and technicians are specially trained to explain these procedures to your child and help him or her feel as comfortable as possible during their tests. Our equipment is specially designed to fit children, so our testing is accurate and as comfortable as possible.

How are allergies diagnosed?

Allergies are most commonly diagnosed through two methods: a thorough history plus physical examination and allergen prick skin testing.

Sometimes additional tests are necessary to help identify a diagnosis. These tests may include laboratory testing, pulmonary function testing, exercise challenges and challenges to certain foods or medications.

How do doctors at Children's Hospital Colorado make a diagnosis?

Our doctors use various tests to diagnose allergies in children. These tests are also often used on an ongoing basis in your child's follow-up care.


At Children's Colorado, the evaluation of a child with a suspected allergic disorder begins with a comprehensive history that includes a thorough review of the child's symptoms, past medical history and family medical history. This is followed by a thorough physical examination.

If the symptoms occur within minutes to a couple of hours after exposure to an allergen and the history is suggestive of an immediate allergic reaction, an allergen prick skin testing is performed. It is important that medications such as antihistamines that might interfere with skin testing, so should be stopped several days before the appointment.

Skin testing

We are thorough, but conservative, in regard to the number of skin tests performed. We realize that some children may be nervous about medical procedures such as skin testing and blood drawing, so we take every precaution to minimize their discomfort during these procedures. Our experienced and sympathetic staff is used to working with children in these situations.

Decisions regarding further testing are based on the needs of each individual child.

How are allergic reactions treated?

There are three basic strategies used to treat allergic conditions: avoidance, medication and immunotherapy (allergy shots).


One of the primary approaches to preventing allergic reactions is to avoid the allergens that cause symptoms. The allergens that trigger symptoms for a given individual are identified by medical history, physical examination, skin testing and occasionally, laboratory testing. Once the triggering allergens are identified, we review effective and discuss strategies to avoid further exposure.


Medications are effective when it is difficult to avoid an allergen, or if the symptoms warrant treatment.

  • Antihistamines block the action of histamine, which is a chemical released by immune cells in the body during an allergic response. Histamines are responsible for a number of the symptoms associated with allergic reactions. Antihistamine medication is available over-the-counter and by prescription. Some medications contain a combination of antihistamines and other medications such as decongestants and/or cough suppressants.
  • Steroids are sometimes used to treat moderate or severe allergic reactions and are only available by prescription. Steroids work by decreasing the inflammation caused by allergic reactions. Topical steroids are available in creams that can be applied directly on the skin, at the site of the allergic reaction. Inhaled steroids are available for allergic conditions of the nose or lungs. Steroids are also occasionally given orally for the management of severe allergic reactions.
  • Leukotriene modifiers are medications that block the production or effects of leukotrienes, which are chemicals involved in causing the inflammation associated with allergic reactions. These medications are used in the treatment of asthma and allergic nasal and ocular symptoms.
  • Asthma medications include "quick-relief" medications and controller medications. Quick-relief medications (such as albuterol) are used to treat sudden onset symptoms including shortness of breath, wheezing and labored breathing. Controller medications (such as inhaled steroids or leukotriene modifiers) are used to calm the airways, reduce inflammation, provide better asthma control and decrease the need for quick-relief medications. The use of asthma medications is individualized for each child based upon their medical history, physical examination results and lung function testing.
  • Anti-IgE is a relatively new medication that is a special antibody that attaches to the allergy antibody (IgE) in the bloodstream and prevents it from reaching the cells involved in the allergic response. It is given as a shot once every 2 to 4 weeks and reserved for the treatment of severe asthmatic patients whose symptoms are triggered by allergic reactions and are unresponsive to other milder forms of therapy. Anti-IgE is only available by prescription.

Immunotherapy (allergy shots)

Allergen immunotherapy is occasionally used to treat patients whose allergens have been clearly identified. Candidates for allergen immunotherapy have significant symptoms for a good portion of the year and remain symptomatic despite attempts to treat their condition In these situations, dilute extracts of the appropriate allergens are prepared and injected into the patient, in gradually increasing amounts over a period of several months, in an attempt to induce tolerance. Once the maintenance dose is reached, the shots are continued every few weeks for several years. A usual course of immunotherapy lasts from 3 to 5 years.

Children's Colorado's Anschutz Medical Campus location offers a Family Health Library to provide information in broad areas such as parenting, child development and medical diagnosis in children. We encourage families to use this great resource as they like.

The following sources are also good resources for information about allergic reactions.

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