Allergic reactions


Allergic reactions are sensitivities to a specific substance, called an allergen , that is contacted through the skin, inhaled into the lungs, swallowed, or injected.


Allergic reactions are common. In fact, the immune response that causes an allergic reaction is similar to that which causes hayfever. Most reactions happen soon after contact with an allergen.

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

Substances that don’t bother most of us (such as venom from bee stings and various foods, medications, and pollens) can trigger allergic reactions in some people.

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

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

Most occur within seconds or minutes after exposure to the allergen, but some can occur after several hours, particularly if the allergen causes a reaction after it is partially digested. 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, very fast and lead to death within 15 minutes if treatment is not received. 


Common allergens include:

  • Plants
  • Pollens
  • Animal dander
  • Bee stings or stings from other insects
  • Insect bites
  • Medications
  • Foods, especially nuts and shellfish


Common symptoms of mild allergic reactions include:

  • Rashes
  • Hives (especially over the neck and face)
  • Itching
  • Nasal congestion
  • Watery, red eyes

Symptoms that may indicate a moderate or severe reaction include:

  • Swelling of the face, eyes, or tongue
  • Difficulty swallowing
  • Wheezing
  • Fear or feeling of apprehension or anxiety
  • Abdominal cramps or abdominal pain
  • Nausea and vomiting
  • Weakness
  • Dizziness or light-headedness
  • Chest discomfort or tightness
  • Difficulty breathing
  • Unconsciousness

First Aid

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 honey 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. Avoid medicated lotions.
  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 for dangerous throat swelling is a very hoarse or whispered voice, or coarse sounds when the person is breathing air in. If the victim is having difficulty breathing, is very weak, or is losing consciousness, call for emergency medical assistance. If necessary, begin rescue breathing and CPR .
  2. Calm and reassure the person.
  3. If the allergic reaction is from bee stings, 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 medication on hand, help the person take or inject the medication. Avoid oral medication if the person is having difficulty breathing.
  5. Take steps to prevent shock . Have the person lie flat, elevate 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.
  6. If the person loses consciousness, apply first aid for unconsciousness and call 911 or your local emergency number.


  • 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 airway.
  • DO NOT Give the person anything by mouth if the person is having trouble breathing.

When to Contact a Medical Professional

  • The person’s allergic reaction is severe or rapidly worsening (over minutes — see above).
  • The person has a history of severe allergic reactions (check for a medical ID tag).


  • Avoid triggers such as foods and medications that have caused an allergic reaction, even a mild one, in the past. This includes detailed questioning about ingredients when eating away from home. Ingredient labels should also be carefully examined.
  • If you have a child who is allergic to certain foods, introduce one new food at a time so you can recognize an allergic reaction.
  • A medical ID tag should be worn by people who know that they have serious allergic reactions.
  • If you have a history of a serious allergic reactions, carry emergency medications (such as diphenihydramine and injectable epinephrine or a bee sting kit) according to your health care 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 affected by this drug.