Anaphylaxis, or anaphylactic shock, is a sudden catastrophic allergic reaction involving the whole body. Immediate medical treatment is essential, without it your heart and circulation may fail and you could die.
What's the cause?
No one is sure why some people get anaphylaxis and some don't. It usually happens to people who are known to have an allergy and the most common cause of anaphylaxis is eating a food to which you are allergic.
Peanuts and tree nuts (such as almonds, brazil nuts, hazelnuts and walnuts) are the foods most likely to provoke a reaction.
Anaphylaxis can also be brought on by fish, shellfish, eggs and dairy products. Even eating a tiny amount of a particular food can cause anaphylaxis.
Allergy to venom from bee and wasp stings can cause the reaction too, as can allergy to latex and drugs such as antibiotics.
What are the symptoms?
The initial reaction is swelling and itching of the area the allergen has entered. So food initially causes swelling and itching of the mouth and throat, while a wasp sting will cause intense itching and swelling around the bite.
A generalised reaction rapidly follows and an itchy rash spreads over the whole body. The face and soft tissues begin to swell and breathing becomes difficult.
The person becomes very agitated – people describe a 'feeling of impending doom' - and their blood pressure begins to drop. At this point the victim collapses and loses consciousness.
These symptoms can develop within a few minutes of contact with the allergen.
What's the treatment?
Anaphylaxis requires emergency treatment because the symptoms of respiratory obstruction and shock develop so quickly. An injection of adrenaline is given to raise blood pressure, relieve breathing difficulties and reduce swelling.
As long as this is done promptly, people normally recover quickly but anyone who's had anaphylaxis should go to hospital for observation regardless. This is because they may need further treatment - such as antihistamines, corticosteroids and occasionally oxygen and intravenous therapy - when the adrenaline wears off.
Providing first aid
Although emergency medical help is essential, there are things that must be done to improve survival chances. If the person is conscious and having breathing difficulties, help them sit up. If they are shocked with low blood pressure, however, they are better off lying flat with their legs raised.
If the person is unconscious, check their airways and breathing and put them in the recovery position.
If you know that the person is susceptible to anaphylaxis, ask if they carry a preloaded adrenaline syringe. If necessary, help the person inject it into the muscle of the thigh.
Then dial 999 for an ambulance and tell the controller that you think the person may have anaphylaxis. If available, antihistamines and steroids should also be given.
To find out about training and courses in your area, contact your nearest branch of the British Red Cross or St John Ambulance (or St Andrew's Ambulance Association in Scotland).
What precautions should I take?
If you have ever had anaphylaxis you must be referred to an allergy clinic for full assessment and to identify the cause of the reaction.
If you or someone you know is prone to anaphylaxis, the following precautions should be taken to prevent future anaphylactic reactions:
- Have your own preloaded adrenaline auto-injector
- Carry your medicines with you at all times and make sure you're familiar with how to use them
- Inform other people at home, work or college about your allergy and where you keep your medicines and how they're used
- Make sure that your medication is easily accessible and check its 'use-by' date regularly
- Wear a special medic alert bracelet or necklace that will inform emergency medical staff about your condition