What I've learned is that there are two separate considerations that determine how one manages a food allergy--
1. sensitivity (that is, what kind of dose is required to cause a reaction)-- some people need to actually eat a bit of an allergen, or something that contains significant amounts of it-- and others, in the minority, live at the other extreme and can't (really) even be AROUND someone handling/eating some allergens
and
2. severity-- which, as Irena notes, can vary significantly even for an individual, and from day to day.
The problem is that threshold dosing can also fluctuate somewhat depending on the person's immune status otherwise. An exposure that my DD might be fine with in October could send her to the hospital in May during the height of grass pollen season. Hormonal shifts, asthma status, etc. all make a difference.
It's very complicated.
