Why does Giovanni not die from Beatrice's breath (he just becomes poisonous himself) in "Rappaccini’s Daughter."
Hawthorne's "Rappaccini's Daughter" is one of those classic stories which is worth discussing. This is a good question with a simple answer--Giovanni had become accustomed to the poison in small doses and was therefore immune to its effects.
When he first arrived, he was given a room directly over the garden and the window was open. We know the poisons in the garden were powerful enough for Doctor Rappaccini to wear a mask at least some of the time. Some of that poison was no doubt carried in the air particles Giovanni unknowingly breathed in every day.
After he and Beatrice developed a speaking relationship, they talked mostly through that same window overlooking the garden. More opportunities for Giovanni's body to become accustomed to the poison. We know this was happening, because one day Signor Baglioni saw Giovanni on the street and almost didn't recognize him--his coloring had become that of Beatrice's, an almost too vivid version of itself.
Finally, once the young couple were spending actual time together (after conveniently being given a key to the garden), they spent it within the confines of the garden. This all happened slowly, of course, and in a way which was virtually unnoticeable to either Giovanni or Beatrice. The final understanding dawns on Giovanni as he sees Beatrice "kill" flowers and flying insects and as he sees his own flesh marked by the poison, as well. If they ever had kissed, which they didn't do in the story, it seems unlikely either would have poisoned the other.