Allergic Reactions



Anaphylaxis is caused by the immune system overreacting to allergens or triggers. It is not always known what triggers it. Common triggers are:

  • Foods and food additives, such as:
    • Peanuts, treenuts, and seeds
    • Fish and shellfish
    • Eggs and cow's milk
  • Insect stings or bites from bees, wasps, hornets, yellow jackets, and fire ants
  • Medicines, such as certain types of:
    • Antibiotics
    • Anesthesia
    • Seizure medicines
    • Muscle relaxants
    • Opioid pain medicines
    • Cancer medicines
  • Vaccines
  • Latex
  • Exercise
  • Blood transfusions
Allergic Reaction to Medication (Hives)
Hives Medication
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Risk Factors

Things that may raise the risk are:

  • Previous anaphylaxis
  • Family or personal history of eczema, hay fever, or asthma
  • Exposure to an allergen
  • Certain immune system problems
  • Sensitivity to latex, more common in:
    • Workers who use latex gloves
    • Children with spina bifida
    • Patients exposed to latex gloves or devices from health care



Symptoms often occur within minutes after contact with an allergen. Some may happen hours later. They may be mild or severe enough to cause death. Symptoms may be:

  • Hives and itching
  • Warmth or redness of skin
  • Swelling, redness, stinging or burning—especially on the face, mouth, eyes, or hands
  • Lightheadedness, headache, or pounding heartbeat
  • Pale skin or blue skin color
  • Problems breathing or swallowing
  • Nausea, vomiting, cramping, diarrhea, or belly pain
  • Loss of consciousness


The doctor will ask about symptoms and past health. A physical exam will be done. This may be enough to make a diagnosis. Blood and urine tests may also be done.

The person may be referred to an allergy doctor.



Anaphylaxis needs medical care right away, including:

  • An epinephrine (adrenaline) injection to help:
    • Open airways
    • Narrow blood vessels
    • Stop itching and hives
    • Ease stomach cramps
  • Corticosteroids or antihistamines—to reduce inflammation and improve breathing
  • Bronchodilators—to open airways
  • IV fluids—to help blood pressure
  • Oxygen

Severe anaphylaxis may require:

  • Cardiopulmonary resuscitation (CPR)
  • Mechanical ventilation—to help keep the upper airway open


To reduce the risk of anaphylaxis:

  • Avoid contact with triggers.
  • Ask the doctor about allergy shots.
  • Carry an epinephrine injector at all times.
  • Wear a medical alert bracelet at all times.

This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.

Edits to original content made by Denver Health.