Allergic reactions and anaphylaxis

Anaphylaxis kills within minutes. The mechanism is straightforward: an immune system overreaction floods the body with histamine and other mediators, dropping blood pressure, closing airways, and collapsing circulation simultaneously. In a hospital, the treatment is also straightforward — epinephrine, immediately. In the field, the obstacle is almost never the drug.

It is hesitation. Providers wait for textbook-perfect symptoms, delay while debating, or reach for antihistamines first. Those delays are what turns a survivable reaction into a fatality.

Educational use only

This page provides general educational information for emergency preparedness scenarios when professional medical care is unavailable. It is not a substitute for professional medical advice, diagnosis, or treatment. Anaphylaxis is a life-threatening emergency — always seek emergency medical care when possible. Use this information at your own risk.

Reaction severity grading

Not every allergic reaction is anaphylaxis. Grading the reaction correctly determines your response. Move through this classification quickly — you have minutes, not hours, to decide.

Mild — skin only

Symptoms confined entirely to the skin and mucous membranes:

Urticaria (hives): raised, red, intensely itchy welts that can appear anywhere on the body and move or expand
Erythema: generalized redness and flushing without raised lesions
Localized angioedema: swelling of a specific area — one eyelid, one lip, one hand — with no airway involvement
Localized itching at the site of exposure (sting site, contact area)

Mild reactions do not involve breathing, blood pressure, the gut, or the cardiovascular system. They are uncomfortable and can progress, but they are not immediately life-threatening on their own.

Response: Antihistamines. Observe closely. Keep epinephrine within reach because mild reactions can escalate.

Moderate — skin plus one systemic sign

Skin symptoms plus one of the following systemic signs:

Nausea, vomiting, or abdominal cramping
Presyncope: dizziness, lightheadedness, or a feeling of impending faintness
Wheezing or mild shortness of breath (airway involvement but not in crisis)
Diaphoresis: sudden cold sweat without exertion
Throat tightness that is noticeable but not obstructing breathing

Moderate reactions require close monitoring and a lower threshold for epinephrine. Many practitioners treat moderate reactions with epinephrine rather than waiting for progression.

Response: Prepare epinephrine for immediate use. Administer if symptoms are escalating rather than stabilizing.

Anaphylaxis — treat immediately

Anaphylaxis is present when any two of the following organ systems are involved after a known or suspected allergen exposure:

Organ system	Signs
Skin/mucosa	Hives, flushing, angioedema, itching
Respiratory	Stridor, wheezing, shortness of breath, hoarse voice, cough
Cardiovascular	Hypotension (low BP), rapid or weak pulse, syncope, chest tightness
Gastrointestinal	Vomiting, diarrhea, severe cramping
Neurological	Confusion, loss of consciousness, sudden extreme anxiety

Exception — single organ system rule: Anaphylaxis is also present if there is any cardiovascular or respiratory compromise alone after allergen exposure, even without skin symptoms. Up to 10–20% of anaphylaxis cases present with no skin signs.

The absence of hives does not rule out anaphylaxis

The classic picture of hives plus throat swelling is textbook, but real presentations deviate from textbooks. A patient who suddenly develops severe hypotension, loses consciousness, or goes into respiratory distress after eating a suspected trigger has anaphylaxis until proven otherwise. Hives are common but not required.

Common anaphylaxis triggers:

Category	Examples
Foods	Peanuts, tree nuts, shellfish, fish, milk, eggs, wheat, sesame
Insect stings	Honeybee, yellow jacket, wasp, hornet, fire ant
Medications	Penicillin-class antibiotics, aspirin and NSAIDs, contrast dye, sulfonamides
Latex	Surgical gloves, rubber bands, balloons, latex catheters
Exercise	Exercise-induced anaphylaxis (alone or in combination with food)
Idiopathic	No identifiable trigger — accounts for up to 30% of cases

Epinephrine: the only first-line treatment

Antihistamines do not treat anaphylaxis. Corticosteroids do not treat anaphylaxis fast enough to matter. Epinephrine is the sole first-line treatment, and nothing replaces it. Every minute of delay in giving epinephrine increases the risk of death.

Epinephrine works by: - Constricting dilated blood vessels to restore blood pressure - Relaxing airway smooth muscle to open bronchospasm - Reducing mucosal swelling (angioedema) - Suppressing ongoing mast cell and basophil mediator release

The drug has a narrow therapeutic window and degrades quickly — epinephrine auto-injectors and drawn-up syringes must be stored correctly and replaced before expiration.

Dosing by weight and age

Epinephrine for anaphylaxis is always intramuscular (IM), into the outer mid-thigh. IM injection into the thigh provides faster absorption than subcutaneous injection or deltoid injection. Never inject IV unless you are in a monitored medical setting — IV epinephrine at these doses causes dangerous arrhythmias.

Patient weight	Dose	Formulation	Route
Adult or child over 30 kg (66 lb)	0.3 mg	Epinephrine 1:1,000 (1 mg/mL)	IM, outer thigh
Child 15–30 kg (33–66 lb)	0.15 mg	Epinephrine 1:1,000 (1 mg/mL)	IM, outer thigh
Infant or child under 15 kg (33 lb)	0.01 mg/kg	Epinephrine 1:1,000 (1 mg/mL)	IM, weight-drawn syringe

For infants under 15 kg (33 lb): Draw up the calculated dose manually. A 10-kg (22 lb) infant receives 0.1 mg (0.1 mL of 1:1,000 solution). Use a 1 mL syringe for accuracy at small volumes.

Repeat dosing: If symptoms are not improving or are worsening after 5 minutes, give a second dose. Approximately 25% of anaphylaxis cases require more than one dose. A third dose may be given after another 5 minutes if available. After three doses without improvement, you are managing refractory anaphylaxis — maximize supportive care and evacuate immediately.

Auto-injector technique (EpiPen, Auvi-Q, generic)

Auto-injectors are designed for use by non-medical personnel under stress. The technique is intentionally simple, but errors — hesitation at the wrong step, injecting into the wrong site — are common.

Remove the safety cap by pulling it straight off. Do not grip the tip end — that is where the needle exits.
Hold the auto-injector in your dominant hand with your thumb closest to the safety cap end (now removed) and fingers wrapped around the barrel. Do not grip the tip.
Press the tip firmly against the outer mid-thigh — the lateral surface halfway between the hip and the knee. Through clothing is acceptable. Jeans, athletic pants, and standard fabric do not prevent delivery.
Push firmly and hold. The click signals needle deployment and drug delivery. Hold in place for 10 full seconds to ensure complete drug delivery.
Remove the device straight out, not at an angle. The needle retracts automatically on removal.
Rub the injection site briskly for 10 seconds to aid drug absorption.
Note the exact time of injection. This is critical for second-dose decisions and for relaying to emergency responders.
Save the used device — do not throw it away. Emergency responders can use the device label to identify the drug, dose, and lot number.

Common errors to avoid: - Injecting into the buttock (slower, less reliable absorption) - Injecting into the hand or finger accidentally (vasoconstriction can cause tissue injury) - Removing the safety cap before pressing to the thigh (risk of accidental discharge) - Holding too briefly — less than 10 seconds risks incomplete delivery

Field note

Train with a trainer auto-injector before you need the real one. The grip, the pressure required to fire, and the instinct to pull back after the click are not intuitive. People who have practiced once make almost no errors. People who have never handled one often hesitate at the moment of deployment. A trainer auto-injector (no needle, no drug) is inexpensive and can be reused for household training.

Drawing epinephrine from a vial

If no auto-injector is available and you have epinephrine 1:1,000 ampules or multi-dose vials:

Draw the calculated dose into a 1 mL tuberculin syringe.
Attach a 25-gauge, 5/8-inch (16 mm) needle — appropriate for most thigh depths.
Clean the thigh skin with an alcohol wipe.
Insert the needle at a 90-degree angle into the outer mid-thigh, subcutaneous to deep muscle.
Pull back the plunger slightly to check for blood return. If blood appears, withdraw and reinsert at a slightly different site — you have entered a vessel.
Inject the dose over 5 seconds.
Record the time.

Positioning and supportive care

Patient position during anaphylaxis is not trivial — cardiovascular collapse can occur within seconds of standing, a phenomenon called empty ventricle syndrome or positional anaphylaxis death.

Standard positioning

Lay the patient flat with legs elevated 12–18 inches (30–45 cm) if they have cardiovascular signs (low blood pressure, faintness, weak pulse). This increases venous return and temporarily supports blood pressure.
Allow sitting upright if the primary symptom is airway distress (wheezing, stridor, throat tightness). Lying flat can worsen respiratory distress.
Recovery position (on their side) if the patient is unconscious or vomiting and breathing is adequate.
Never allow standing or walking during active anaphylaxis or in the recovery period. Deaths have occurred when improving patients stood to use the bathroom.

Oxygen

If oxygen is available and you are trained in its use, deliver high-flow oxygen at 10–15 liters per minute via non-rebreather mask during anaphylaxis. Oxygen does not replace epinephrine but supports tissue perfusion during the hemodynamic crisis.

Antihistamines as adjuncts

Diphenhydramine (Benadryl) — 25 mg for children 6–12, 50 mg for adults over age 12 — relieves hive and itch symptoms after epinephrine is given. It does not treat hypotension, bronchospasm, or airway angioedema. Give it after epinephrine, not instead of it.

H2 antihistamines (famotidine, ranitidine) address the histamine receptors that H1 antihistamines (diphenhydramine) miss. A combination of H1 and H2 blockers provides more complete antihistamine coverage, but again: adjunct only, never primary treatment.

Airway management for angioedema

Angioedema is swelling of the deep skin layers — most dangerous when it involves the tongue, lips, and throat. Allergic angioedema of the airway can close within minutes.

Severity signs — escalating urgency

Lip and tongue swelling with normal voice and breathing: Give epinephrine, monitor closely. Patient is not yet in crisis.
Hoarse or muffled voice: The vocal cords are beginning to swell. Give epinephrine immediately (if not already given) and prepare for rapid deterioration.
Stridor (a high-pitched crowing sound on inhalation): Significant airway narrowing is present. This is the last warning before complete obstruction. Give epinephrine, position upright, and consider all available airway management options.
Inability to speak or swallow: Near-complete obstruction. Immediate airway intervention required.

What you can do without surgical equipment

Upright position: Gravity reduces mucosal swelling slightly — keep angioedema patients upright, not flat.
Epinephrine repeat dosing: Each additional dose of epinephrine provides another window of airway relaxation. Do not withhold a second or third dose because the patient already received one.
Bag-valve-mask (BVM) ventilation: If the patient loses consciousness and stops breathing, BVM ventilation can push air past a partially obstructed airway. The pressure required will be higher than normal.
Heliox if available: A helium-oxygen mixture reduces the turbulence of air moving through a narrowed airway. It is not commonly stocked in field kits but is worth knowing about.

Angioedema that does not respond to epinephrine

Hereditary angioedema (HAE) is a genetic condition that causes recurrent angioedema through a completely different mechanism — bradykinin, not histamine. It does not respond to epinephrine, antihistamines, or steroids. If a patient has a known HAE diagnosis, their specific treatment (C1-esterase inhibitor concentrate, icatibant, or ecallantide) is the only effective therapy. Standard anaphylaxis treatment does not work and you should focus on evacuation.

Biphasic reactions

A biphasic reaction is a second wave of anaphylaxis that occurs after apparent recovery from the first, without any re-exposure to the trigger. It represents a return of mediator release, not a new allergen encounter.

Frequency: Up to 20% of anaphylaxis cases
Timing: Most biphasic reactions occur within 8 hours of the initial reaction, but documented cases have appeared as late as 72 hours later
Severity: The second wave can be more severe than the first and can occur more rapidly
Risk factors for biphasic reaction: Slow initial response to epinephrine, unknown trigger, large initial exposure, delayed administration of the first epinephrine dose

Observation protocol

After symptoms resolve following epinephrine administration:

Keep the patient in a supervised observation setting for a minimum of 4–6 hours. In preparedness contexts when transport to a hospital is not possible, extend observation to 24 hours.
Monitor every 30 minutes: assess breathing, skin, pulse, mental status, and blood pressure if equipment allows.
Keep epinephrine immediately accessible throughout the observation period. If you only had one dose and gave it, send for more.
Document the time of symptom resolution and the time each epinephrine dose was given. Relay this to emergency responders or the patient's physician.
If any anaphylaxis symptoms return — hives plus breathing, low blood pressure, throat tightness — treat as a new anaphylaxis event: give epinephrine immediately.

Field note

Biphasic reactions are the reason "they seemed fine" is not the same as "they are fine." Patients who recover from anaphylaxis and immediately resume normal activity without observation are at real risk. The clearest predictor of a severe biphasic reaction is a delayed first dose of epinephrine — the longer the initial reaction went untreated, the more likely it returns with force.

Insect sting field protocol

Hymenoptera stings (bees, wasps, yellow jackets, hornets, fire ants) are one of the most common anaphylaxis triggers. Field-specific considerations differ from indoor exposures.

Immediate steps after a sting

Remove the stinger if one is visible (bees leave a barbed stinger; wasps do not). Scrape it out with a card or fingernail — do not squeeze, which injects more venom.
Assess the reaction within 5 minutes. A localized welt and itch at the sting site is normal and not anaphylaxis.
Watch for systemic signs over the next 10–20 minutes: hives beyond the sting site, throat tightness, vomiting, dizziness. These signal anaphylaxis — give epinephrine.
For known bee sting allergy with an auto-injector: the threshold for administration is lower. Give epinephrine at the first systemic sign, not after confirming the full picture.
Move away from the area. Stinging insects release alarm pheromones that recruit additional insects to sting. Leave the area rapidly.
Apply a cold compress to the sting site (20 minutes on, 20 minutes off) for localized pain and swelling.

Multiple stings: More than 10 stings in an adult, or more than 5 in a child, can deliver enough venom to cause a toxic (non-allergic) reaction that mimics anaphylaxis. Treat with the same protocol — epinephrine and supportive care — and prioritize evacuation.

Carrying epinephrine in the field

Anyone with a known insect allergy should carry two epinephrine auto-injectors at all times during outdoor activities. The second device provides backup if the first fails or if a second dose is required before the first can be replaced. Store auto-injectors at 15–25°C (59–77°F) — avoid leaving them in a vehicle in summer heat, which can exceed 60°C (140°F) and degrade the drug. A degraded epinephrine solution turns pink or brown; clear pale yellow is correct.

Prevention and preparedness

Allergen identification and avoidance

Document every household member's known and suspected allergies. For food allergies, include all names the allergen may appear under on labels (peanut oil, arachis oil, groundnut oil — all the same). In food storage rotation, check that substitute ingredients don't contain cross-reactive allergens — someone with a severe wheat allergy who rotates to barley is still being exposed to gluten.

Kit requirements for known-allergy households

Item	Quantity	Notes
Epinephrine auto-injector (EpiPen Jr, 0.15 mg)	2	For children 15–30 kg (33–66 lb)
Epinephrine auto-injector (EpiPen, 0.3 mg)	2	For adults and children over 30 kg
Diphenhydramine (Benadryl) 25 mg tablets	24	Adjunct to epinephrine for skin symptoms
Famotidine (Pepcid) 20 mg tablets	12	H2 antihistamine adjunct
Oral prednisone 20 mg tablets	12	Prescribed steroid for biphasic prevention (prescription required)
Medical alert bracelet or card	1	Identifies allergy, drug, and dose for first responders
Trainer auto-injector	1	For household practice — no needle, no drug

Allergy readiness checklist

Document all household allergy diagnoses, including allergen name, typical reaction severity, and prior anaphylaxis history
Carry two epinephrine auto-injectors whenever known-allergic household members are away from home
Check auto-injector expiration dates every six months and replace before expiry
Store auto-injectors at room temperature, never in a hot vehicle or frozen in a freezer
Practice auto-injector technique on a trainer device — every adult in the household should be able to do this
Know the location of the nearest emergency room capable of managing anaphylaxis
Maintain allergen-free food segregation in stored food supplies — review labels when rotating stock
Post the biphasic reaction monitoring protocol where caregivers can reference it

Anaphylaxis management overlaps directly with shock recognition and management, because hemodynamic collapse from anaphylaxis is distributive shock requiring the same positional and fluid support. For managing the infection risks that follow insect stings and allergic skin breakdown, see wound infection recognition and treatment. When building your household medical kit to include epinephrine, auto-injectors, and antihistamines, stockpiling and medical supplies covers the sourcing and storage considerations in detail.