[timtyrrell]

I am the parent of twins. Their mother ate multitudes of peanut M&M's and similar items when pregnant. One twin has zero peanut allergies, the other one has deadly allergies and we are at the ER at least once a year from food contamination.

[femto]

On the assumption that such allergies have a genetic component, presumably the twins aren't identical?

[swores]

It's also possible for things which do have genetic components to _also_ have environmental triggers, so its not impossible that, for example, identical twins who happened to get different levels of exposure to peanuts in their first year of life based on random luck of which family member ate peanuts near them at which times, or something like that, could lead to different outcomes even if genetics were the reason that both twins were at risk of developing such an allergy.