A peanut allergy is caused by certain proteins, which trigger your immune system to over-react to what is (for most people) a harmless substance.

Normally, your immune system completely ignores these peanut proteins. Peanuts are food after all.

For some reason, some people develop a strong reaction to peanuts. For some people, even the tiniest fragment of peanut – barely visible to the naked eye – can trigger a big reaction.

The only danger for such people is the reaction itself, but the reaction can be strong enough for some people to be very serious.

For people with a highly sensitive peanut allergy, just 2mg of certain peanut proteins is enough to set them off.

The average peanut has about 200mg of these proteins, so one hundredth of a peanut is enough to cause a problem for the most sensitive of people with a peanut allergy.