While I have read many commentaries against the use of condoms for oral sex siting the reduction of stimulation, I have used condoms for oral sex, giving and receiving, and I did feel a measure of medical security comfort from it. I also did not experience any noticeable lacking in my enjoyment (which could be attributed to the skill of the provider). And to your second question, yes, on those occasions without the use of condoms I have worried about catching STI's. Now that I'm past my engaging escort years, and am no longer "tempting" for masseurs, those worries are behind me.