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Allergic reactions

Contents of this page:

Illustrations

Allergic reactions
Allergic reactions
Dermatographism - close-up
Dermatographism - close-up
Dermatographism on the arm
Dermatographism on the arm
Hives (urticaria) on the arm
Hives (urticaria) on the arm
Hives (urticaria) on the chest
Hives (urticaria) on the chest
Hives (urticaria) - close-up
Hives (urticaria) - close-up
Hives (urticaria) on the trunk
Hives (urticaria) on the trunk
Dermatographism on the back
Dermatographism on the back
Dermatographism - arm
Dermatographism - arm
Allergic reactions
Allergic reactions

Definition    Return to top

Allergic reactions are sensitivities to substances, called allergens, that are contacted through the skin, inhaled into the lungs, swallowed, or injected.

Considerations    Return to top

Allergic reactions are common. The immune response that causes an allergic reaction is similar to the response that causes hay fever. Most reactions happen soon after contact with an allergen.

Many allergic reactions are mild, while others can be severe and life-threatening. They occur more often in people with a family history of allergies.

Substances that don't bother most people (such as venom from bee stings and certain foods, medications, and pollens) can trigger allergic reactions in certain people.

While first-time exposure may only produce a mild reaction, repeated exposures may lead to more serious reactions. Once a person has had an allergic reaction (is sensitized), even a very limited exposure to a very small amount of allergen can trigger a severe reaction.

Allergic reactions can be mild or serious. They can be confined to a small area of the body or may affect the entire body.

Most severe allergic reactions occur within seconds or minutes after exposure to the allergen. However, some reactions can occur after several hours, particularly if the allergen causes a reaction after it has been ingested. In very rare cases, reactions develop after 24 hours.

Anaphylaxis is a sudden and severe allergic reaction that occurs within minutes of exposure. Immediate medical attention is needed for this condition. It can get worse very fast and lead to death within 15 minutes if treatment is not received.

Causes    Return to top

Common allergens include:

Symptoms    Return to top

Common symptoms of a mild allergic reaction include:

Symptoms of a moderate or severe reaction include:

First Aid    Return to top

For a mild to moderate reaction:

  1. Calm and reassure the person having the reaction, as anxiety can worsen symptoms.
  2. Try to identify the allergen and have the person avoid further contact with it. If the allergic reaction is from a bee sting, scrape the stinger off the skin with something firm (such as a fingernail or plastic credit card). Do not use tweezers; squeezing the stinger will release more venom.
  3. If the person develops an itchy rash, apply calamine lotion and cool compresses. You may also apply over-the-counter cortisone cream.
  4. Watch the person for signs of increasing distress.
  5. Get medical help. For a mild reaction, a physician may recommend over-the-counter medications (such as antihistamines).

For a severe allergic reaction (anaphylaxis):

  1. Check the person's airway, breathing, and circulation (the ABC's of Basic Life Support). A warning sign of dangerous throat swelling is a very hoarse or whispered voice, or coarse sounds when the person is breathing air in. If necessary, begin rescue breathing and CPR.
  2. Call 911.
  3. Calm and reassure the person.
  4. If the allergic reaction is from a bee sting, scrape the stinger off the skin with something firm (such as a fingernail or plastic credit card). Do not use tweezers -- squeezing the stinger will release more venom.
  5. If the person has emergency allergy medication on hand, help the person take or inject the medication. Avoid oral medication if the person is having difficulty breathing.
  6. Take steps to prevent shock. Have the person lie flat, raise the person's feet about 12 inches, and cover him or her with a coat or blanket. Do NOT place the person in this position if a head, neck, back, or leg injury is suspected or if it causes discomfort.

DO NOT    Return to top

When to Contact a Medical Professional    Return to top

Call for immediate medical emergency assistance if:

Prevention    Return to top

References    Return to top

Simons FE. Anaphylaxis. J Allergy Clin Immunol. 2008;121:S402-S407.

Update Date: 4/28/2008

Updated by: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Stuart I. Henochowicz, MD, FACP, Associate Clinical Professor of Medicine, Division of Allergy, Immunology, and Rheumatology, Georgetown University Medical School. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

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