There are no data that allow definitive answers, ie whether intraoral ejaculation or swallowing semen increases risk higher than otherewise. It would make sense, but nobody knows for sure.
CDC has a CYA attitude; if there is any theoretical risk at all, warn against it. Although CDC's prevention messages have been (forcibly) influenced by politics in recent years, in this case I don't think the message results from that, but from the general tendency of all buraucracies to protect themselves from even a small risk of legal challenge.
Nobody seriously recommends routine use of condoms for all oral sex. It would further reduce the already small risks of disease transmission, but for most people the suggestion doesn't meet the laugh test.
HHH, MD
When I say risk I am referring to HIV risk, I realize other STD's are a much higher risk. FYI - Along with the Herpes FAQ's I believe an HIV FAQ section would be very beneficial along with just a general FAQ section regarding chance of exposure, test times, etc....
There are just way too many people asking the same variation of multiple questions within days of each other, why don't you do a follow-up to your original question?
Because this isn't a follow up to my other question, this is a completely different question!!