Scientists say that this backs up the hygiene hypothesis that cleaner homes tend to increase the risk of childhood allergies.

They found that high income and hygiene habits could be increasing susceptibility as they discovered a link between peanut allergy in children and their families socio-economic status.

With the number of peanut allergies among children increasing the team from the American College of Allergy, Asthma, and Immunology (ACAAI) believe that one reason might be due to the wealth of their families.

The theory suggests that a lack of early childhood exposure to germs increases the chance for allergic diseases, that over sanitisation might suppress the natural development of the immune system.

Peanut allergy can be life-threatening with sufferers going into anaphylactic shock, but more commonly it causes itching in the mouth, a rash and swelling of the face, lips, eyes and tongue.

Allergies occur when the body’s immune system mistakes proteins in food as threatening and reacts as if there was an infection invading.

Common food allergies in children are milk, eggs, peanuts, fish and shellfish but almost any food, including fruits and vegetables can cause a reaction.

Study author Dr Sandy Yip said: “Overall household income is only associated with peanut sensitisation in children aged one to nine years.

“This may indicate that development of peanut sensitisation at a young age is related to affluence, but those developed later in life are not.”
Her team looked at 8,306 patients, 776 of which had an elevated antibody level to peanuts.

Peanut allergy was generally higher in men and racial minorities across all age groups. The researchers also found that peanut specific antibody levels peaked between the ages of 10 and 19, but tapered off after middle age.

ACAAI president Doctor Stanley Fineman said: “While many children can develop a tolerance to food allergens as they age, only 20 per cent will outgrow a peanut allergy.

“It’s important that children remain under the care of a board-certified allergist to receive treatment.”

According to ACAAI, peanut allergy affects an estimated 400,000 school-aged children in the America while in the UK it is estimated to effect 1.8 per cent of children at school entry.

The team recommends peanut-allergic individuals be vigilant in restaurants, where peanuts may appear as a hidden ingredient.

The new study is presented at the American College of Allergy, Asthma and Immunology (ACAAI) Annual Scientific Meeting.

There is no cure for food allergies but some studies have shown success in exposing children to minute doses of the food can desensitise them.

In 2009 doctors at Addenbrooke’s hospital in Cambridge gave four children tiny amounts of peanut flour, in carefully controlled circumstances, gradually increasing the dose over a number of days. Eventually they could eat ten peanuts safely.

The experiment should not attempted outside a research setting, they warned.

Pregnant women used to be warned not to eat peanuts or products containing peanuts for fear of increasing the risk of allergies in their child, however scientists now know this makes no difference and some studies have suggested it reduces the risk of the child suffering reactions.

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By Rebecca Smith