The number of people admitted to hospital with life-threatening anaphylactic shock – involving sudden swelling, breathlessness and low blood pressure – has increased by at least 700 per cent in the last two decades.

Anaphylaxis is often triggered by an allergy, such as one to bee stings or peanuts. The number of people affected by allergies has trebled in the past 20 years and it is estimated that a third of the population will develop an allergy at some point in their lives.

The first guidelines for treating the condition, published today by the National Institute for Clinical Excellence (Nice), say doctors should record the circumstances immediately before the reaction to help identify the cause and ensure an adrenaline injector is given to patients after emergency treatment before they are referred to a specialist. Patients can then give themselves a shot of adrenaline, which may be life saving in the event of another attack.

Anaphylaxis causes about 20 deaths a year in otherwise healthy people from heart attacks or suffocation caused by the swelling of tissues in the mouth and throat.

About 50,000 people in England suffer an anaphylactic attack over the course of their lifetime, one in 1,300 of the population, according to Nice. Hospital admissions for the condition increased from about 300 a year in 1990 to more than 2,100 in 2004, a seven-fold increase, and are likely to have risen further since.

Food allergies affect 4 per cent of adults and 6 per cent of children under the age of three. Shellfish and nuts are the most common triggers. Some studies suggest allergies to peanuts has more than doubled in the past decade, affecting more than one in 100 children. Fergus Macbeth, director of the Centre for Clinical Practice at Nice, said: "After an anaphylactic episode, there is often a risk of it happening again. Further investigation is therefore needed in all cases to try to identify the cause and assess the risk of the person having another anaphylactic reaction."

Mandy East, national co-ordinator at the Anaphylaxis Campaign, said: "We welcome this Nice guideline which gives clear recommendations on what to do following emergency treatment for a suspected anaphylactic episode.

"For the patient, an anaphylactic reaction is extremely worrying and it is essential that specialist care is offered in order for a diagnosis to be confirmed and for the risk of recurrent episodes to be reduced."