There has been a sharp increase in the number of people admitted to hospital in England because of allergic reactions, figures reveal.
Allergic reactions can be serious
A study in the British Medical Journal shows hospital admissions more than trebled over 11 years.
In 1990, 1,960 people were admitted to hospital because of allergic reactions. By 2001, that had increased to 6,752.
This suggested people might be more susceptible to allergens which cause such reactions, the researchers said.
The research team from St George's Hospital Medical School in London analysed official figures for hospital admissions.
They found that more than 49,000 people had been admitted because of severe allergic reactions over the 11-year period.
Of these, 39% were admitted for urticaria - a severe outbreak of itchy hives.
Some 26% were admitted for anaphylaxis - a sudden, severe and potentially life-threatening reaction, which can cause dangerous swelling of the lips or face and lead to breathing problems.
Another 18% were admitted for food allergies, with the remaining 17% admitted for angio-oedema - deep swelling underneath the skin, often around the eyes and lips, and sometimes on hands and feet.
Admissions for anaphylaxis and food allergies rose most over the 11 years.
They were up five-fold compared with 1990. Admission rates for urticaria more than doubled while almost twice as many people were hospitalised for angio-oedema.
The researchers said greater public awareness of allergies or changes in the way they were treated are unlikely to be behind the sharp increase.
They suggested that the rise was a result of more people developing allergies.
"These increases could be caused by increasing exposure to environmental risk factors such as peanuts and other foods or latex, to an increased susceptibility in the population to these allergens or a combination of these factors," they wrote.
John Foreman, professor of immunopharmacology at University College London, said scientists were unsure why more people were suffering allergic reactions.
"Nobody really knows why allergies are increasing," he told BBC News Online.
"There is evidence that there has been an increase in allergic asthma, which is the principal cause of hospital admissions for allergies in the last decade or two.
"Nobody really knows why this is. One theory is the so-called muck theory, that children are not as exposed to soil organisms as they used to be and this leaves them more prone to allergies.
"This is controversial but it is the only idea that I know of the may explain the increase."