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allergic reactions Alternative Names acquired sensitivity reaction, induced sensitivity reaction Definition An allergic reaction is an immune system response to exposure to a specific substance. What is going on in the body? Allergic reactions are fairly common. Most reactions happen soon after contact with an allergen. An allergen is a trigger that causes the reaction after touching a certain part of the body. The blood may be exposed from an injection. The blood or gut may be exposed from swallowing an allergen. The lungs may be exposed from inhaling the allergen. The skin may be directly exposed to an allergen. Usually these reactions are mild and can be treated at home with simple methods. However, some people have a sudden, life-threatening allergic reaction within minutes, called anaphylaxis. Anaphylaxis can progress rapidly and result in shock and even death if medical help is not obtained quickly. Usually, the first exposure produces only a very mild reaction or no reaction at all. For some people, repeated exposure may lead to more serious reactions. Even a small amount of a trigger can lead to a serious reaction in some people. Allergic reactions can affect small areas or the entire body. Most reactions occur within seconds or minutes of exposure. However, some reactions can occur days or weeks after exposure. What are the signs and symptoms of the condition? Mild allergic reactions may cause the following: coughing, sneezing, and nasal congestion fever hives, or raised swellings on the skin that itch itching joint pain or muscle aches redness of the skin or a rash swelling of the tongue, eyelids, or face worsening of asthma or an asthma flare-up, which makes breathing difficult Severe reactions may cause severe forms of the above changes as well as: abdominal distress or cramping chest discomfort difficulty swallowing dizziness or light-headedness unconsciousness What are the causes and risks of the condition? There are few things that do not cause an allergic reaction in some people. However, most people never have an allergic reaction. Those with a family history of allergies are more likely to develop them. People with asthma, hay fever, or a skin condition known as eczema are more likely to develop allergies. Following are some of the common triggers: bee stings foods such as peanuts and shrimp, which can trigger a food allergy medicines metals mold pets with feathers or fur pollens or plants synthetic materials tiny organisms such as bacteria What can be done to prevent the condition? The first allergic reaction generally cannot be avoided. However, the best way to prevent a second attack is by avoiding the trigger. This can be difficult in some cases, especially with common substances. id="1876" pub="1" type="medenc"> Breast-feeding instead of bottle-feeding is thought to reduce the chance of a child having certain food allergies. How is the condition diagnosed? Diagnosis of an allergic reaction begins with a medical history and physical examination. In some cases, special skin tests or other allergy testing may be needed to determine the trigger. In skin testing, small amounts of the suspected substance can be injected under the skin. If a person is allergic to the substance, a skin reaction usually occurs. What are the long-term effects of the condition? An allergic reaction has no long-term effects if the trigger is avoided. Many allergies are mild and pose little threat to the affected person. Some allergies are life threatening and may cause death. What are the risks to others? Allergic reactions are not contagious and pose no risk to others. What are the treatments for the condition? First aid for the treatment of mild to moderate reactions includes the following steps: Reassure the person to calm him or her down and lessen the severity of the reaction. If possible, identify and remove the trigger. If the person develops a rash, apply calamine lotion and cool compresses. Over-the-counter antihistamines, such as diphenhydramine, can be taken to decrease the allergic response. Prescription medicines may be needed in some cases to open the airways. Steroids, such as prednisone, may be used to decrease swelling and open airways. A severe allergic reaction is treated as above with a few extra measures. Many people who have severe allergic reactions carry medicine, such as epinephrine, in case exposure to the trigger occurs. The person may need help injecting the medicine. The person's airway and breathing should be checked. If necessary, cardiopulmonary resuscitation, or CPR, should be started. The person should be lying down. His or her feet should be raised above head level. However, if the person has or may have a head, neck, back, or leg injury, he or she should not be moved. The person should be covered with a blanket or coat for warmth. What are the side effects of the treatments? Antihistamines can cause drowsiness. Prednisone can cause stomach problems, mood swings, and sleep problems. These side effects are generally very mild. Medicines used to open the airways can cause shakiness and abnormal heart rate. These, too, tend to be mild. Epinephrine can cause significant anxiety, shakiness, and abnormal heart rate. This medicine is often administered in the doctor's office or emergency room. What happens after treatment for the condition? Anyone who has a known serious allergic reaction should wear a medical alert bracelet at all times. This tag identifies the allergy. The substance to which the person is allergic should be avoided. Friends and relatives should be made aware of the allergy in case of an exposure or emergency. Those with an allergic reaction to a medicine should tell their healthcare provider. How is the condition monitored? The affected person should avoid the substance to which he or she is allergic. People with severe allergies may be given a medicine for injection in case of an exposure. Any new or worsening symptoms should be reported to the healthcare provider.

Author: James Broomfield, MD Date Written: 08/06/99 Reviewer: William M. Boggs, MD Date Reviewed: 08/21/01 Potential conflict of interest information for reviewers available on request