Anaphylaxis

What is anaphylaxis?

Anaphylaxis is a severe allergic reaction that develops within minutes and can be fatal. It affects breathing and circulation, not just the skin. Adrenaline given into the outer thigh is the only treatment that reverses it, and it should be given immediately rather than waiting to see whether symptoms settle. Antihistamines do not treat anaphylaxis.

Causes

• Food allergens, most often peanuts, tree nuts, shellfish, milk and egg
• Insect stings, particularly wasp and bee
• Medicines including penicillin and anti inflammatory drugs
• Latex
• Exercise combined with a trigger food in rare cases
• No identified trigger in idiopathic cases

Symptoms

• Swelling of the tongue, lips or throat
• Difficulty breathing or noisy wheezy breathing
• A hoarse voice or difficulty swallowing
• Widespread hives or flushing
• Sudden dizziness, collapse or loss of consciousness
• Rapid heartbeat with cold clammy skin
• Sudden severe vomiting or abdominal pain
• A sense that something is very badly wrong

Risk factors

• Previous anaphylaxis, which is the strongest predictor
• Known food or drug allergy
• Asthma, particularly if poorly controlled
• Mast cell disorders
• Adolescence and young adulthood for food triggered reactions

Diagnosis

• Clinical diagnosis made on the spot, treatment must not wait for tests
• Serum tryptase taken during and after the reaction
• Specialist allergy referral after any episode
• Skin prick and specific IgE testing to confirm the trigger
• Supervised challenge testing in selected cases

Treatment

• Intramuscular adrenaline into the outer thigh immediately
• Call emergency services even if symptoms improve
• Lie the person flat with legs raised, or sit up if breathing is hard
• A second adrenaline dose after five minutes if no improvement
• Oxygen and intravenous fluids in hospital
• Observation in hospital because symptoms can return hours later
• Two adrenaline autoinjectors carried at all times afterwards

Self care

• Carry two adrenaline autoinjectors everywhere, every day
• Check expiry dates and replace before they run out
• Teach family, friends, school or colleagues how to use them
• Wear medical alert jewellery
• Read every food label and ask about ingredients when eating out
• Keep an allergy action plan written and accessible
• Keep asthma well controlled, since it worsens outcomes

When to see a doctor

Book an appointment if:

• After any suspected allergic reaction, however mild
• To arrange allergy testing and identify the trigger
• To be prescribed and trained on autoinjectors
• If reactions are becoming more frequent or severe
• Before starting a new medicine you have reacted to before
• Annually to review the action plan and replace devices

Some symptoms need emergency care rather than an appointment. See the warning signs listed above.

Prevention

• Strict avoidance of the identified trigger
• Always declare allergies before medical and dental procedures
• Inform restaurants clearly and check every time
• Consider immunotherapy for venom allergy
• Keep autoinjectors within reach rather than at home

Outlook

With immediate adrenaline the outlook is excellent and most people recover fully. Deaths are usually associated with delayed adrenaline, so timing matters more than anything else. Reactions can return several hours after apparent recovery, which is why hospital observation follows treatment. Many childhood milk and egg allergies resolve, whereas peanut, tree nut and shellfish allergies usually persist.

Related conditions

Common questions