Allergic Reactions and Anaphylaxis: Emergency First Aid

Allergic reactions occur when the immune system overreacts to a normally harmless substance called an allergen. While most allergic reactions are mild and self-limited, anaphylaxis is a severe, life-threatening systemic reaction that requires immediate recognition and treatment. The World Health Organization estimates that 1 to 2 percent of the global population will experience anaphylaxis in their lifetime, and the incidence is rising. This guide covers the spectrum of allergic reactions, the critical steps for recognizing and treating anaphylaxis, and the correct use of epinephrine auto-injectors.

Understanding Allergic Reactions

An allergic reaction begins when the immune system produces immunoglobulin E antibodies against a specific allergen. On subsequent exposure, these antibodies trigger mast cells and basophils to release histamine, leukotrienes, and other inflammatory mediators. These chemicals produce the classic symptoms of allergy: vasodilation, increased vascular permeability, smooth muscle contraction, and mucus secretion.

Common allergens include foods (peanuts, tree nuts, milk, eggs, shellfish, wheat, soy), insect stings (bees, wasps, hornets, fire ants), medications (penicillin, NSAIDs, contrast dye), and latex. The American Academy of Allergy, Asthma and Immunology notes that food allergies affect approximately 8 percent of children and 5 percent of adults in the United States, and peanut allergy alone has tripled in prevalence over the past two decades.

Mild to Moderate Allergic Reactions

Mild allergic reactions are typically limited to the skin and mucous membranes. Symptoms include hives (raised, red, itchy welts), localized swelling, itchy or watery eyes, runny nose, sneezing, and mild gastrointestinal discomfort such as nausea or stomach cramps.

Treatment involves avoiding further allergen exposure, taking oral antihistamines such as diphenhydramine or cetirizine, and applying cool compresses to itchy skin. The American Academy of Dermatology recommends calamine lotion or oatmeal baths for widespread hives. Most mild reactions resolve within hours with antihistamine treatment.

However, a mild reaction can progress to anaphylaxis, especially in people with a history of severe reactions. Anyone with a known severe allergy should carry epinephrine at all times, even if past reactions were mild.

Recognizing Anaphylaxis

Anaphylaxis is defined by the rapid onset of symptoms involving two or more organ systems after exposure to a known or suspected allergen. The American College of Allergy, Asthma and Immunology uses the following criteria for diagnosis:

• Acute onset of skin or mucosal symptoms (hives, itching, flushing, swollen lips/tongue/uvula) PLUS either respiratory compromise (dyspnea, wheezing, stridor, hypoxia) or reduced blood pressure (hypotension, syncope, incontinence)

OR

• Two or more of the following after exposure to a likely allergen: skin symptoms, respiratory symptoms, hypotension, persistent gastrointestinal symptoms

OR

• Reduced blood pressure after exposure to a known allergen (systolic BP below 90 mmHg or drop of more than 30 percent from baseline)

The hallmark of anaphylaxis is that it is a systemic reaction affecting multiple body systems simultaneously. The person may feel a sense of impending doom, which is a recognized symptom of severe anaphylaxis.

Epinephrine: The First-Line Treatment

Epinephrine is the only first-line treatment for anaphylaxis. It works by causing vasoconstriction (raising blood pressure), bronchodilation (opening the airways), and reducing mediator release from mast cells. The AAAAI and ACAAI joint guidelines state that epinephrine should be administered immediately at the first sign of anaphylaxis, without delay.

Epinephrine auto-injectors (EpiPen, Auvi-Q, Adrenaclick) deliver a fixed dose. For adults and children over 66 pounds (30 kg), the dose is 0.3 mg. For children weighing 33 to 66 pounds (15 to 30 kg), the dose is 0.15 mg.

How to use an auto-injector:

1. Form a fist around the device with the orange (or red) tip pointing downward.
2. Remove the blue safety cap (for EpiPen) or outer cap (for Auvi-Q).
3. Swing and firmly push the orange tip into the outer mid-thigh. The device can be administered through clothing.
4. Hold for 3 seconds (EpiPen) or until the device signals completion (Auvi-Q beeps).
5. Remove the device and massage the injection site for 10 seconds.
6. Call 911 immediately.
7. Note the time of administration.

The Mayo Clinic emphasizes that epinephrine should be administered in the thigh muscle. Injection into a vein or finger is dangerous and should be avoided. Auto-injectors are designed to prevent this when used as directed.

Patients often report a second dose is needed because symptoms do not resolve or recur. The AAAAI guidelines recommend carrying two epinephrine auto-injectors at all times and administering a second dose 5 to 15 minutes after the first if symptoms persist or worsen.

Positioning During Anaphylaxis

Position the person lying flat with legs elevated if they feel faint or have low blood pressure. This is the shock position that promotes blood return to the heart and brain. If the person is having difficulty breathing, allow them to sit up, as this position optimizes diaphragmatic movement. Do not ask the person to stand or walk, as standing can precipitate sudden cardiac arrest in anaphylaxis (empty vena cava syndrome).

If the person is unconscious and breathing normally, place them in the recovery position on their side. If they are unconscious and not breathing normally, begin CPR immediately. See our CPR guide for complete resuscitation protocols.

Antihistamines and Adjunct Medications

Antihistamines such as diphenhydramine (Benadryl) and cetirizine (Zyrtec) are useful for mild allergic reactions but are NOT a substitute for epinephrine in anaphylaxis. The AAAAI explicitly states that antihistamines work too slowly to reverse the life-threatening features of anaphylaxis and may mask the progression of symptoms.

H2 blockers such as famotidine (Pepcid) can be used alongside H1 antihistamines for additional symptom relief. Corticosteroids like prednisone may help prevent biphasic reactions (recurrence of symptoms hours after the initial episode) but do not act quickly enough for acute management. Albuterol inhalers can provide temporary relief for bronchospasm but do not treat hypotension or laryngeal edema.

Food Allergies and Label Reading

The Food Allergen Labeling and Consumer Protection Act (FALCPA) requires that food manufacturers clearly list the presence of any of the major food allergens: milk, eggs, fish, crustacean shellfish, tree nuts, peanuts, wheat, and soybeans. In 2021, sesame was added as the ninth major allergen under the FASTER Act. Always read ingredient labels, even on products you purchase regularly, as manufacturers change formulations without notice.

The AAAAI advises that people with food allergies should be cautious with buffets, bakeries, and restaurants where cross-contact with allergens is more likely. Dining out requires clear communication with restaurant staff about allergen needs. Many restaurants now provide allergen menus or can modify dishes to accommodate allergies. Children with food allergies should have an emergency action plan on file with their school, and school staff should be trained on epinephrine administration.

Biphasic Anaphylaxis

Between 1 and 20 percent of anaphylaxis cases involve a biphasic reaction — a recurrence of symptoms 1 to 8 hours after the initial episode without additional allergen exposure. The risk is highest in people with severe initial reactions, those requiring multiple epinephrine doses, and those with delayed epinephrine administration.

This is why anyone treated for anaphylaxis should be observed in an emergency department for at least 4 to 6 hours after symptom resolution, even if they feel completely better after the first epinephrine dose.

Frequently Asked Questions

Can I use an expired epinephrine auto-injector? The FDA advises that expired epinephrine may be less effective due to degradation. However, in a life-threatening emergency where no alternative exists, using an expired device is better than doing nothing. Epinephrine degrades slowly; most auto-injectors retain significant potency for months past the expiration date. Replace devices before they expire.

What if I am not sure it is anaphylaxis? The AAAAI guidelines state that epinephrine is safe and should be used when in doubt. The risks of untreated anaphylaxis far exceed the risks of unnecessary epinephrine. Transient side effects include pallor, tremor, palpitations, and anxiety, which resolve as the medication wears off.

Can food allergies develop later in life? Yes. While many food allergies appear in childhood, adult-onset food allergies are increasingly recognized. Shellfish, tree nuts, and finned fish are the most common adult-onset food allergies. See our first aid guide for general emergency response information.

How do I prevent allergic reactions? Strict allergen avoidance is the cornerstone of prevention. Read food labels carefully, inform restaurant staff about allergies, wear a medical alert bracelet indicating allergies, carry epinephrine auto-injectors at all times, and create an anaphylaxis action plan with your allergist. The AAAAI provides free downloadable action plans on their website.

Can stress make allergic reactions worse? Yes. Psychological stress can increase mast cell reactivity and lower the threshold for anaphylaxis. Some individuals have stress-induced idiopathic anaphylaxis. Managing stress is a recommended component of comprehensive allergy care.

School and Workplace Allergy Preparedness

The CDC’s Voluntary Guidelines for Managing Food Allergies in Schools recommend that schools maintain stock epinephrine (epinephrine that is not prescribed to a specific student) for use in emergencies. As of 2023, the majority of US states have laws requiring schools to maintain undesignated epinephrine auto-injectors. Parents should ensure their child’s allergy action plan is updated annually and that epinephrine is not expired. Teachers, bus drivers, and cafeteria staff should receive annual training on recognizing anaphylaxis and using auto-injectors.

In the workplace, the AAAAI recommends that employers with cafeterias or food service provide allergen information, that first aid stations be equipped with epinephrine, and that designated first aid responders be trained in anaphylaxis management. Occupational allergies to latex, cleaning chemicals, and food products are also common and should be accommodated through engineering controls and personal protective equipment.

Conclusion

Anaphylaxis is a medical emergency that demands immediate action. The difference between a good outcome and a tragic one often comes down to whether epinephrine was administered promptly. Every second counts — do not wait to see if symptoms will improve, and do not substitute antihistamines for epinephrine. People with known severe allergies should carry two epinephrine auto-injectors, educate their family, friends, and coworkers on how to use them, and have an anaphylaxis action plan in place. For anyone without a known allergy who experiences sudden, unexplained allergic symptoms involving multiple body systems, treat as anaphylaxis and call 911 immediately. Epinephrine is safe, effective, and life-saving. By spreading awareness about anaphylaxis recognition and treatment, we can help ensure that no one dies from a preventable allergic emergency.