Allergic reactions
Allergic reactions are sensitivities to substances called allergens that come into contact with the
skin, nose, eyes, respiratory tract, and gastrointestinal tract. They can be breathed into the lungs,
swallowed, or injected.
Considerations
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 can be
confined to a small area of the body, or they may affect the entire body. The most severe form is
called anaphylaxis or anaphylactic shock. Allergic reactions occur more often in people who
have a family history of allergies.
Substances that don't bother most people (such as venom from bee stings and certain foods,
medicines, and pollens) can trigger allergic reactions in certain people.
First-time exposure may produce only a mild reaction. Repeated exposures may lead to more
serious reactions. Once a person has had an exposure or an allergic reaction (is sensitized), even
a very limited exposure to a very small amount of allergen can trigger a severe reaction.
Most severe allergic reactions occur within seconds or minutes after exposure to the allergen.
Some reactions can occur after several hours, particularly if the allergen causes a reaction after it
has been eaten. 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. Without treatment, anaphylaxis can get
worse very quickly and lead to death within 15 minutes.
Causes
Common allergens include:
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Animal dander
Bee stings or stings from other insects
Foods, especially nuts, fish, and shellfish
Insect bites
Medicines
Plants
Pollens
Symptoms
Common symptoms of a mild allergic reaction include:
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Hives (especially over the neck and face)
Itching
Nasal congestion
Rashes
Watery, red eyes
Symptoms of a moderate or severe reaction include:
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Abdominal pain
Abnormal (high-pitched) breathing sounds
Anxiety
Chest discomfort or tightness
Cough
Diarrhea
Difficulty breathing, wheezing
Difficulty swallowing
Dizziness or lightheadedness
Flushing or redness of the face
Nausea or vomiting
Palpitations
Swelling of the face, eyes, or tongue
Unconsciousness
First Aid
For a mild to moderate reaction:
Calm and reassure the person having the reaction. Anxiety can make symptoms worse.
Try to identify the allergen and have the person avoid further contact with it.
1. If the person develops an itchy rash, apply cool compresses and an over-the-counter
hydrocortisone cream.
2. Watch the person for signs of increasing distress.
3. Get medical help. For a mild reaction, a health care provider may recommend over-thecounter medications, such as antihistamines.
For a severe allergic reaction (anaphylaxis):
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 in air. If necessary, begin rescue breathing and CPR.
1. Call 911.
2. Calm and reassure the person.
3. 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.
4. If the person has emergency allergy medicine on hand, help the person take or inject the
medicine. Avoid oral medicine if the person is having difficulty breathing.
5. Take steps to prevent shock. Have the person lie flat, raise the person's feet about 12
inches (30 centimeters), and cover them 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
If a person is having an allergic reaction:
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Do not assume that any allergy shots the person has already received will provide
complete protection.
Do not place a pillow under the person's head if he or she is having trouble breathing.
This can block the airways.
Do not give the person anything by mouth if the person is having trouble breathing.
When to Contact a Medical Professional
Call for medical assistance (911) right away if:
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The person is having a severe allergic reaction. Do not wait to see if the reaction is
getting worse.
The person has a history of severe allergic reactions (check for a medical ID tag).
Prevention
To prevent allergic reactions:
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Avoid triggers such as foods and medicines that have caused an allergic reaction in the
past. Ask detailed questions about ingredients when you are eating away from home.
Carefully check ingredient labels.
If you have a child who is allergic to certain foods, introduce 1 new food at a time in
small amounts so you can recognize an allergic reaction.
People who have had serious allergic reactions should wear a medical ID tag and carry
emergency medicines (such as a chewable form of Chlor-Trimeton and injectable
epinephrine or a bee sting kit) according to your provider's instructions.
Do not use your injectable epinephrine on anyone else. They may have a condition (such
as a heart problem) that could be made worse by this drug.
References
Lieberman P, Nicklas RA, Randolph C, et al. Anaphylaxis -- a practice parameter update 2015.
Ann Allergy Asthma Immunol. 2015;115(5):341-384. PMID: 26505932
www.ncbi.nlm.nih.gov/pubmed/26505932.
Wasserman SI. Approach to the patient with allergic or immunologic disease. In: Goldman L,
Schafer AI, eds. Goldman's Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders;
2016:chap 249.