I had an allergic reaction to my boyfriend's cat.
What is the implied subject of 起こす in this sentence? By default I would expect "I", but "I caused an allergic reaction to my boyfriend's cat" would certainly be a strange thing to say.
The only subject that seems to make sense is "an allergen"; a rather specialist implied subject.
Perhaps I'm misunderstanding how the sentence works. Is there a meaning of 起こす which would fit here that makes this sentence clearer? Or is there some other way of thinking about the sentence?