Just what they told me in med school
I have done a lot of bareback, but I was just lucky I did not catch anything. I had a roommate that did the same girl I did three days earlier and he was on penicillin for 10 days.
My med professor said the the germ gets in a male's uretha and that is where the infection begins if it isn't flushed out in less that a minute. So if you penetrate and don't urinate or ejaculate in the first minute, chances are you will be infected if she has anything. This does not apply to aids or heptitis. I am not a doctor, I did not finish, but that is what the old professor told us young guys about going out on weekends.