[derefr]

> Plus, so many foods list what they "may contain" traces of X, but never really quantify how much of a trace. Which actually may be a good thing about intentionally adding sesame, because at least it makes the amount consistent.

I mean, they don’t usually… know? They know that the assembly line for product X is physically near an assembly line for product Y that contains peanuts, and so X may have some peanut particulate floating through the air and landing on it. It would be a different amount of particulate at different times of day, different humidity, etc; and so different individual bars of product X could end up with different amounts of trace contaminants. (Almost always none, since they do try to avoid these effects; they just can’t guarantee that they’ve been successful, or that they’ll be successful in perpetuity.)

Or alternately, if the manufacturer is a job-shop (produces different things for different customers, retooling between each job) then they can’t guarantee that they’ve cleaned out a perfect 100% of traces of previous job materials out of their assembly line when they start up a new production run. (The theoretically perfect way to solve this is to have separate job-shops that only deal with jobs containing allergen X — but with the combinatorial number of allergens, and a shop having to dedicate itself to only processing a particular combination [A, B, not-C, not-D], that’s mostly impractical.)

[LorenPechtel]

They don't know, but we can be pretty confident that it's no more than a trace.

If eating the wrong thing can kill it makes no difference, "may contain" is the same as "contains". However, if eating the wrong thing will simply mess up your day "may contain" is a very different thing than "contains".

And if I learn I react to product X so be it, I simply don't eat X.