Allergic Reactions & Anaphylaxis

Anaphylaxis is a severe, life-threatening allergic reaction that kills rapidly if not treated. In the UK, approximately 20 people die from anaphylaxis each year; in the US the figure is approximately 1,000–1,500 annually. What makes these deaths particularly tragic is that most are preventable with a single injection of epinephrine — and in many cases, the person who died had an auto-injector with them but it was not used, used too late, or used incorrectly.

Epinephrine (adrenaline) is the only first-line treatment for anaphylaxis. Antihistamines and steroids are not substitutes. They act too slowly. The window between anaphylactic reaction and airway closure can be as short as 5–10 minutes. Understanding the difference between a mild reaction and anaphylaxis, using an auto-injector without hesitation, and knowing what comes next can make the difference between a statistic and a survivor.

The Allergic Reaction Spectrum

Mild to Moderate Allergic Reaction

Symptoms are localised or do not involve the airway or circulation:

• Skin: hives (urticaria), redness, itching
• Eyes: watering, redness, itching (allergic conjunctivitis)
• Nose: runny nose, sneezing
• Mild lip or face swelling (not throat)

Management: Oral antihistamine (e.g., loratadine, cetirizine, chlorphenamine) and observation. Monitor closely for progression. Call for help if any severe symptoms develop.

Anaphylaxis

Anaphylaxis involves multiple body systems, typically including at least one of: airway, breathing, or circulation compromise.

Signs — any combination of:

• Airway: throat tightening, difficulty swallowing, stridor (high-pitched breathing sound), swollen tongue or throat, hoarse voice
• Breathing: wheeze, shortness of breath, coughing, laboured breathing
• Circulation: rapid pulse, falling blood pressure, pallor, dizziness, collapse
• Skin: hives, flushing, generalised itching, angioedema (deep swelling of the face, lips, or throat)
• GI tract: nausea, vomiting, abdominal cramps, diarrhoea
• Neurological: anxiety, sense of doom, confusion, loss of consciousness

⚠️ Anaphylaxis does not always include an obvious skin reaction. Some anaphylactic episodes present primarily with cardiovascular collapse with minimal or no skin signs. If there has been known allergen exposure and the person is collapsing or struggling to breathe, treat as anaphylaxis.

Common Triggers

Category	Examples
Foods	Peanuts, tree nuts, fish, shellfish, milk, eggs, wheat, sesame
Medications	Penicillin and related antibiotics, NSAIDs, aspirin, contrast dye
Insect stings	Bee, wasp, hornet venom
Latex	Latex gloves, medical equipment, balloons
Exercise	Exercise-induced anaphylaxis (sometimes food-dependent)
Unknown	Idiopathic anaphylaxis (no identifiable trigger)

Using an Epinephrine Auto-Injector (EpiPen)

Epinephrine reverses the effects of anaphylaxis by constricting blood vessels (raising blood pressure), relaxing airways (reducing bronchospasm), and suppressing the immune response causing the reaction.

The most widely used auto-injectors are the EpiPen (0.3 mg adult dose; 0.15 mg junior dose) and the Jext, AUVI-Q / Allerject, and generic equivalents. All follow similar operation principles.

Administering an EpiPen

1. Confirm anaphylaxis — do not delay for uncertainty; if anaphylaxis is possible, use it. Epinephrine in a person who does not have anaphylaxis causes a fast heartbeat and anxiety — uncomfortable but not dangerous. Epinephrine withheld from a person who has anaphylaxis can be fatal.
2. Remove the blue safety cap (pull off straight — do not twist)
3. Hold the pen in your dominant hand with your thumb on the opposite end from the needle (hold like a hammer)
4. Push the orange end firmly against the outer thigh — directly through clothing is fine; no need to remove trousers
5. Hold for 10 seconds — you will hear a click indicating the needle has deployed and the dose is being delivered
6. Remove and massage the site for 10 seconds
7. Check for the orange needle guard to confirm the dose was delivered (it extends to cover the needle after use)
8. Call emergency services immediately if you have not already done so — even if symptoms improve, the person must go to hospital

Thigh vs Other Locations

The outer thigh (anterolateral) is the correct injection site. It provides rapid absorption. Do not inject into the buttock (absorption is slow and variable) or the vein.

Second Dose

If symptoms do not improve within 5–15 minutes and a second auto-injector is available, give a second dose in the opposite thigh. A second auto-injector should always be prescribed alongside the first for this reason.

⚠️ Using an expired auto-injector is better than not using one at all. Epinephrine degrades over time but does not suddenly become inert at the expiry date. Use it if nothing else is available.

Positioning

The correct position depends on the dominant symptoms:

Dominant Symptom	Position
Breathing difficulty, wheeze	Sitting upright — allows lung expansion
Faintness, low blood pressure, dizziness	Lying flat with legs raised
Unconscious and breathing	Recovery position
Unconscious, not breathing	CPR position; begin CPR

Do not allow the person to sit or stand up suddenly if they have been lying — sudden postural change can cause cardiac arrest in anaphylaxis with low blood pressure.

After Epinephrine — What Happens Next

Epinephrine has a short duration of action — typically 15–20 minutes. This means:

1. The reaction can return as epinephrine wears off
2. All anaphylaxis patients must go to hospital regardless of how well they appear after epinephrine
3. In hospital, they will receive IV antihistamines, IV steroids, and observation for at least 6–12 hours

Biphasic Reaction

A second wave of anaphylactic symptoms can occur 1–72 hours after the initial reaction — even after apparently complete recovery and even after epinephrine. This is called a biphasic reaction and occurs in approximately 5–20% of anaphylaxis cases. This is one reason why all anaphylaxis cases require hospital observation.

Anaphylaxis Without an Auto-Injector

If epinephrine is not available:

• Call emergency services immediately and state clearly "anaphylaxis"
• Keep the person positioned for their symptoms
• If they carry antihistamines, give them — they do not treat anaphylaxis effectively but may slow mild symptoms
• Prepare for CPR if the person loses consciousness
• If the person has a known bee sting allergy and has been stung, scrape the stinger out with a card or fingernail — do not use tweezers (squeezes more venom)

Living with Severe Allergies — Planning

For people with known severe allergies:

• Always carry two auto-injectors — one may fail or be used; the second is backup
• Carry medical ID (bracelet, card, phone medical ID) identifying the allergy and that epinephrine is prescribed
• Inform people around you — family, colleagues, school staff, sports coaches
• Know your triggers and avoid them — but understand accidental exposure can still occur
• Have an action plan — a written plan from your allergist specifying exactly when to use the auto-injector and what to do afterward

Quick Reference

Situation	Action
Mild allergic reaction	Antihistamine; observe; no epinephrine yet
Anaphylaxis suspected	Epinephrine immediately; emergency services
EpiPen use	Remove cap; push to outer thigh; hold 10 sec; massage site
Position (breathing difficulty)	Sit upright
Position (faintness/collapse)	Lie flat; raise legs
After epinephrine	Hospital regardless — biphasic reaction risk
No improvement after 15 min	Second dose if available
No auto-injector	Emergency services; antihistamines; prepare CPR
Expired auto-injector	Use it — better than nothing

This guide provides general information on anaphylaxis recognition and management. Anyone at risk of anaphylaxis should be under the care of an allergist and have a personalised action plan. All anaphylactic episodes require emergency medical evaluation regardless of apparent recovery.