Anaphylaxis

Causes of anaphylaxis

No one's sure why some people get anaphylaxis and others don't. It usually happens to people who are known to have an allergy. The most common cause is eating a food to which you're 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 triggered by fish, shellfish, eggs and cow's milk. 

Even eating a tiny amount of a particular food can cause anaphylaxis. 

Allergy to from bee and wasp stings can cause anaphylaxis too, as can allergy to latex rubber and drugs such as antibiotics.

Sometimes, anaphylaxis only occurs under certain conditions. Exercise-induced anaphylaxis (EIA), for example, only occurs after increased levels of exercise. One sub-type of EIA, food-dependent EIA, only occurs when a person has eaten a certain food that they are sensitive too and then they exercise - the food or exercise alone does not produce symptoms. 

There are even variations in this - in specific-food EIA a specific food (such as wheat, celery or shellfish) is known to be the offending allergen, but in non–specific-food EIA no specific food is known, but eating any food prior to exercise causes symptoms of EIA. Another type of EIA is medication-dependent exercise-induced anaphylaxis where the reaction is triggered when someone taking certain drugs exercises. 

Certain anaphylaxis-prone individuals are unable to identify any obvious trigger. The anaphylaxis can occur for no apparent reason and is called idiopathic anaphylaxis. 

Symptoms of anaphylaxis

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 sting. In EIA, the skin becomes generally warm, itchy and red. 

A generalised reaction rapidly follows within minutes and a raised itchy rash spreads over the whole body. The face and soft tissues begin to swell and breathing becomes difficult as the throat closes. 

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.

Anaphylaxis in adults tend to affect blood circulation, with loss of pressure and shock. Children tend to develop wheezing and fatal airway obstruction. Food-allergic children with coexistent asthma have a higher anaphylaxis risk.

In anaphylaxis, the symptoms develop within a few minutes of contact with the allergen, so immediate treatment is essential. 

Anaphylaxis treatments

Anaphylaxis requires emergency treatment because the symptoms of respiratory obstruction and shock develop so quickly. An injection of adrenaline must be 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. They may need further treatment - such as antihistamines, corticosteroids and, occasionally, oxygen and intravenous therapy - when the adrenaline wears off.

Preventing anaphylaxis

If you've 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 your medication is easily accessible and check its use-by date regularly - adrenaline in an autoinjector has a limited shelf life (usually 18 or 24 months depending on the make) and can become inactive fairly rapidly after the use-by date. An out of date adrenaline auto-injector is better than no adrenaline at all but to be sure, you should see your GP regularly to arrange for them to supply you with a new one
• Wear a MedicAlert bracelet or necklace to inform emergency medical staff of your condition

You may need to repeat this procedure with your second auto-injector if there's no improvement of symptoms after five minutes. Do this on your way to A&E.

It's worth knowing that adrenaline auto-injectors are one of a short list of medicines which can be used, in an emergency, on someone other than the person they were prescribed for. So if a person unexpectedly has an anaphylactic reaction, it may help to see if anyone else is carrying adrenaline.

What about future risks?

If you have one anaphylactic reaction, there's no predicting how severe subsequent reactions may be. They may be identical, more or less severe. Coexistent asthma is a risk factor for more severe reactions.

You're unlikely to outgrow anaphylaxis and will need to take constant precautions. Never assume you'll be OK because you haven't had a severe reaction for a long time.

Following food anaphylaxis, check for hidden ingredients on labels and take care with restaurant and takeaway meals. Nuts and eggs, for example, may have a variety of names and are often added to processed foods. It's wise to see a dietician for help with excluding all allergy-provoking foods from your diet.

Not all unpleasant reactions are anaphylaxis. Sometimes panic attacks, hysteria, inhaling a food particle, epileptic seizures, fish toxins, lung clots (pulmonary embolism), fainting spells and heart attacks can closely resemble anaphylactic reactions.

First aid for anaphylaxis

Although emergency medical help is essential, there are things that must be done to improve survival chances. If the person affected is conscious and having breathing difficulties, help them sit up. If they're shocked with low blood pressure, they're 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 their thigh muscle. Then dial 999 for an ambulance and tell the controller you think the person may have anaphylaxis. If available, antihistamines and steroids should also be given.