What causes allergies in some people?

Asked by: Jake Mellor, Manchester

Allergies are caused by an overactive immune system. There’s evidence that this is inherited, but many studies have also shown that growing up in an excessively clean environment can trigger allergies. People from big families tend to have been exposed to more bacteria and have a lower chance of developing allergies.

If you had skin cream containing peanut oil as a baby, you are more likely to be allergic to peanuts as an adult, and soy in formula milk may also trigger peanut allergies, perhaps because the proteins have similar molecular shapes.

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