I know that I have a genetic-based flaw in my nose that results in the occasional nosebleed. My mother has it too.
I get nosebleeds when I drink coffee and take vitamins at the same time. I think it's because of dehydration.
Thus, alcohol dehydrates, so I suppose that when i drink and get a nosebleed it's because i am dehydrated and that weak spot in my nose cracks and I bleed.
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