Packed with Danger

WHY PEANUTS cause some of the worst cases of food allergy - including fatalities - is not clear.

Between 1 and 2 per cent of the population is allergic to certain food proteins: the peanut is responsible for the biggest proportion of cases and causes the worst reactions. It contains more than 30 types of proteins, but scientists are examining the handful most likely to send the immune system haywire.

The allergy results in an overproduction of histamine in the body, producing swollen blood vessels, local inflammation or a fall in blood pressure. Scientists believe an initial exposure to peanut proteins in early life sensitises a child's immune system to produce a key antibody, IgE, which causes subsequent protein exposures to trigger the release of histamine.

The worst outcome is anaphylactic shock, when the airways of the lungs constrict, the blood pressure falls dangerously and the tongue swells. Peanut allergy was once considered a mainly American problem, but with the increased consumption of peanut butter and other "finger foods", the number of British sufferers has grown.

Babies may become sensitised through infant formulas containing peanut protein or oil. Others could develop an allergy in the womb or from the breast milk of mothers who ate peanut products.