Allergic Reaction

An allergic reaction is the body's way of responding to an "invader." When the body senses a foreign substance, called an antigen, the immune system is triggered. The immune system normally protects the body from harmful agents such as bacteria and toxins. Its overreaction to a harmless substance (an allergen) is called a hypersensitivity, or allergic, reaction.

• Anything can be an allergen. Common dust, pollen, plants, medications, certain foods, insect venoms, viruses, or bacteria are examples of allergens.

• Reactions may be in one spot, such as a small skin rash or itchy eyes, or all over, as in a whole body rash.

• A reaction may include one or several symptoms.

In rare cases, an allergic reaction can be life threatening (see Anaphylaxis). Each year in the United States, over 400 people die from allergic reactions to penicillin, and over 50 people die from allergic reactions to bee and fire ant stings.

Most allergic reactions are much less serious, such as a rash from poison ivy or sneezing from hay fever. The reaction depends on the person but is sometimes unpredictable.

Allergies are very common.

Almost anything can trigger an allergic reaction.

• The body's immune system has a patrol of white blood cells, which produce antibodies.
  • When the body is exposed to an antigen, a complex set of reactions begins.

  • The white blood cells produce an antibody specific to that antigen. This is called "sensitization."

  • The job of the antibodies is to detect and destroy substances that cause disease and sickness. In allergic reactions, the antibody is called immunoglobulin E, or IgE.

• This antibody promotes production and release of chemicals and hormones called "mediators."
  • Histamine is one well-known mediator.

  • Mediators have effects on local tissue and organs in addition to activating more white blood cell defenders. It is these effects that cause the symptoms of the reaction.

  • If the release of the mediators is sudden or extensive, the allergic reaction may also be sudden and severe.

• Your allergic reactions are unique to you. For example, your body may have learned to be allergic to poison ivy from repeated exposure.

• Most people are aware of their particular allergy triggers and reactions.
  • Certain foods, vaccines and medications, latex rubber, aspirin, shellfish, dust, pollen, mold, animal dander, and poison ivy are famous allergens.

  • Bee stings, fire ant stings, penicillin, and peanuts are known for causing dramatic reactions that can be serious and involve the whole body.

  • Minor injuries, hot or cold temperatures, exercise, or even emotions may be triggers.

  • Often, the specific allergen cannot be identified unless you have had a similar reaction in the past.

• Allergies and the tendency to have allergic reactions run in some families. You may have allergies even if they do not run in your family.

• Many people who have one trigger tend to have other triggers as well.

• People with certain medical conditions are more likely to have allergic reactions.
  • Severe allergic reaction in the past

  • Asthma

  • Lung conditions that affect breathing, such as chronic obstructive pulmonary disease (COPD)

  • Nasal polyps

  • Frequent infections of the nasal sinuses, ears, or respiratory tract

  • Sensitive skin

The look and feel of an allergic reaction depends on the body part involved and the severity of the reaction. Some reactions affect many areas, others affect just one area. Reactions to the same allergen vary by individual.

• Anaphylaxis is the term for any combination of allergic symptoms that is rapid, or sudden, and potentially life threatening. Call an ambulance immediately if you suspect anaphylaxis.
  • One sign of anaphylaxis is shock. Shock has a very specific meaning in medicine: the organs of the body are not getting enough blood because of dangerously low blood pressure. Shock may lead rapidly to death. The person in shock may be pale or red, sweaty or dry, confused, anxious, or unconscious.

  • Breathing may be difficult or noisy, or the person may be unable to breathe.
    
    
• Shock is caused by sudden dilation of many or large blood vessels. This is brought on by the action of the mediators. If the drop in blood pressure is sudden and drastic, it can lead to unconsciousness, even cardiac arrest and death.

• Symptoms of an allergic reaction include any, some, or many of these:
  • Skin - Redness, itching, swelling, blistering, weeping, crusting, rash, eruptions, or hives (itchy bumps or welts)

  • Lungs - Wheezing, tightness, cough, or shortness of breath

  • Head - Swelling of the face, eyelids, lips, tongue, or throat; headache

  • Nose - Stuffy nose, runny nose (clear, thin discharge), sneezing

  • Eyes - Red (bloodshot), itchy, swollen, or watery

  • Stomach - Pain, nausea, vomiting, diarrhea, or bloody diarrhea

Because allergic reactions can progress and worsen in minutes, medical attention is always recommended for all but the most minor and localized symptoms.

If the symptoms of your reaction get worse over a few days, or if they do not get better with recommended treatment and removal of the allergen, call your health care provider.

Tell your health care provider if you have any allergic symptoms after using a drug or other treatment he or she prescribed for you (see Drug Allergy).

Allergic reactions can be dangerous. Sudden, severe, widespread reactions require emergency evaluation by a medical professional. Call an ambulance if you or someone around you has any of the following with an allergic reaction:

• Sudden, severe, rapidly worsening symptoms

• Exposure to an allergen that previously caused severe or bad reactions

• Swelling of the lips, tongue, or throat

• Wheezing, chest tightness, loud breathing, or trouble breathing

• Confusion, sweating, nausea, or vomiting

• Widespread rash

• Collapse or unconsciousness

For typical allergic reactions, your health care provider will examine you and ask you questions about your symptoms and their timing. Blood tests and x-rays are not needed except under unusual circumstances.

In case of severe reaction, you will be evaluated quickly in the emergency department. The first step for the health care provider is to judge the severity of the allergic reaction.

• Blood pressure and pulse are checked.

• An examination determines whether you need help breathing.

• Often, an IV line is placed in case you need anti-allergy medications quickly.

• If you can speak, you will be asked about triggers and previous reactions.

• Blood tests and x-rays are not helpful.

|Self-Care at Home|

Avoid triggers! If you know you have an allergic reaction to peanuts, for example, do not eat them. Go out of your way to avoid foods prepared with or around peanuts (see Food Allergy).

Self-care at home is not enough in severe reactions. A severe reaction is a medical emergency.

• Do not attempt to treat or "wait out" severe reactions at home. Go immediately to a hospital emergency department.

• If no one is available to drive you right away, call 911 for emergency medical transport.

• For more information on what to do in a severe reaction, see Anaphylaxis.

Small reactions with mild symptoms usually respond to nonprescription allergy medications.

• An oral antihistamine, such as diphenhydramine (Benadryl). Caution – These may make you too drowsy to drive or operate machinery safely. They can affect concentration and interfere with children's learning in school. These medications should be taken for only a few days.

• For rashes, an anti-inflammatory steroid cream such as hydrocortisone

For small, localized skin reactions, try cold, wet cloths or ice. Try applying a bag of frozen vegetables wrapped in a towel.

|Medical Treatment|

Generally, medication is the treatment of choice after the allergen is removed. For more information on removing environmental allergies from your home, see Allergy-proof your home.

Very severe reactions may require other therapy, such as oxygen for breathing difficulties or intravenous fluids to boost blood pressure in anaphylactic shock. Patients with very severe reactions usually require hospitalization.

|Medications|

Anti-allergy medications are of many types. The choice of medication and how it is given depends on the severity of the reaction.

For relief of long-term allergies such as hay fever or reactions to dust or animal dander, the following medications may be prescribed:

• Long-acting prescription antihistamines, such as cetirizine (Zyrtec), fexofenadine (Allegra), and loratadine (Claritin), can relieve symptoms without causing sleepiness. They are meant to be taken for months at a time, even indefinitely. Most have to be taken only once a day and last for 24 hours.



• Nasal corticosteroid sprays are widely prescribed for nasal symptoms not relieved by antihistamines. These prescription medications work very well and are safe, without the side effects of taking steroids by mouth or injection. These sprays take a few days to take effect, and must be used every day. Examples are fluticasone (Flonase), mometasone (Nasonex), and triamcinolone (Nasacort).

For severe reactions, the following medications are usually given right away to rapidly reverse symptoms:

• Epinephrine
  
  
  • This drug is given only in very severe reactions (anaphylaxis).
  
  
  
  • It is injected and acts as a bronchodilator (dilates the breathing tubes).
  
  
  
  • It also constricts the blood vessels, increasing blood pressure.
  
  
  
  • Another medication with similar effects may be given instead.
  
  
  
  • For a less severe reaction involving the respiratory tract, an inhaled bronchodilator may be used, as in asthma.
     
• Antihistamines, such as diphenhydramine (Benadryl)
  
  
  • This drug is given IV or in a muscle to reverse the actions of histamine.
  
  
  
  • Oral diphenhydramine is usually enough for a less severe reaction.
     
• Corticosteroids
  
  
  • One from this group of drugs is usually given IV at first for rapid reversal of the effects of the mediators.
  
  
  
  • These drugs should not be confused with the steroids taken by athletes to build muscle and strength.
  
  
  
  • These drugs reduce swelling and many other symptoms of allergic reactions.
  
  
  
  • You will probably need to take an oral corticosteroid for several days after this.
  
  
  
  • Oral corticosteroids are often given for less severe reactions.
  
  
  
  • A corticosteroid cream or ointment may be used for skin reactions.
  
  
  
  • Corticosteroid nasal sprays reduce the discomfort of a "stuffy" nose.

Other medications may be given as needed.

• In some people, cromolyn sodium nasal spray prevents allergic rhinitis, inflammation of the nose that occurs as an allergic reaction.



• Decongestants can restore sinus drainage, relieving symptoms such as nasal congestion and swelling and runny nose and sinus pain (pain or pressure in the face, especially around the eyes). They are available in oral forms and as nasal sprays. They should be used for only a few days, as they may have side effects such as high blood pressure, rapid heartbeat, and nervousness.

For more information, see Understanding Allergy and Hay Fever Medications.

|Other Therapy|

Allergy shots: These are given to some people who have persistent and disruptive allergy symptoms.

• The shots do not treat symptoms, but by altering the immune response they prevent future reactions. (This is referred to as immunotherapy.)

• Treatment involves a series of shots, each containing a slightly greater amount of the antigen(s) that cause the reaction.

• Ideally, the person will become "desensitized" to the antigen(s) over time.

• The effectiveness of shots varies by individual.

|Follow-up|

Allergic reactions are sometimes unpredictable.

• Always watch for a return of symptoms as medications wear off or exposure to an allergen trigger continues.

• Return of symptoms may be sudden and severe.

• Anticipate a possible return of the reaction and a need to return to the medical office or emergency department.

Use all medications only as instructed or as prescribed.

• Therapy to suppress an allergic reaction may involve long-acting antihistamines and other anti-allergy medications.

• Severe cases may require a course of steroid treatment lasting as long as 4 weeks.

|Prevention|

Most people learn to recognize their allergy triggers; they also learn to avoid them.

An allergy specialist (allergist) may be able to help you identify your triggers. Several different types of allergy tests are used to identify triggers.

• Skin testing is the most widely used and the most helpful. There are several different methods, but all involve exposing the skin to small amounts of various substances and observing the reactions over time.

• Blood tests (RAST) generally identify IgE antibodies to specific antigens.

• Other tests involve eliminating certain allergens from your environment and then re-introducing them to see if a reaction occurs.

People with a history of serious or anaphylactic reactions may be prescribed an auto-injector, sometimes called a bee-sting kit. This contains a premeasured dose of epinephrine (EpiPen is one brand name). You carry this with you and inject yourself with medication immediately if you are exposed to a substance that causes you to have a severe allergic reaction.

There is some evidence that breast-fed infants are less likely to have allergies than bottle-fed infants.

|Outlook|

Most allergic reactions respond well to medications.

• Hives, swelling, breathing difficulties, even anaphylaxis often improve and disappear in minutes to hours.

• Some rashes take several days to heal.

• Your health care provider may want to monitor you for a few hours.

• A dangerous allergic reaction may warrant an overnight stay in the hospital.

Allergic reactions will continue with continued exposure to the allergen or trigger.

• You need to avoid any triggers you know cause an allergic reaction.

• Ingested, inhaled, or injected allergy triggers may take days for the body to eliminate.

• Continued medical therapy is necessary for continued exposure.

You may be referred to an allergy specialist if you continue having reactions.

American Academy of Allergy, Asthma & Immunology
555 East Wells Street, Suite 1100
Milwaukee, WI 53202-3823
(414) 272-6071
Patient Information and Physician Referral Line: (800) 822-2762

American College of Allergy, Asthma & Immunology
85 West Algonquin Road, Suite 550
Arlington Heights, IL 60005

National Institute of Allergy and Infectious Diseases
Office of Communications and Public Liaison
6610 Rockledge Drive, MSC 6612
Bethesda, MD 20892-6612
(301) 496-5717

|Web Links|

Food Allergy and Anaphylaxis Network

National Institute of Environmental Health Sciences, Asthma Research at NIEHS

Nemours Foundation, Allergic Reactions

American Academy of Allergy Asthma & Immunology, Tips to Remember: What is an Allergic Reaction

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Author: William Larry Haith, DO, FAAEM, Consulting Staff, Department of Emergency Medicine, Southern Maine Medical Center.

Editors: Scott H Plantz, MD, FAAEM, Research Director, Assistant Professor, Department of Emergency Medicine, Mount Sinai School of Medicine; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, ; Anthony Anker, MD, FAAEM, Attending Physician, Emergency Department, Mary Washington Hospital, Fredericksburg, VA.