How does baker's yeast survive the oven though?

How does baker's yeast survive the oven though? Just a sciency question - I can't eat yeasted bread OR Sach. Boulardii yeast, both of them give me instant problems, but was always curious if the commercial baker's yeast in premade bread is just something some of us are allergic to, or does it actually survive the over-300 degrees baking temperatures...