Herpes is transmitted via skin-to-skin contact, but only when the virus is active (whether a visible herpes outbreak or viral shedding). You CAN’T get herpes from saliva or blood. You CAN get genital herpes from someone going down on you and they have cold sores (whether it’s visible or not) — cold sores (aka mouth herpes mostly caused by HSV-1) magically turns to genital herpes in an instant (in fact, 50% of all new genital herpes cases are from oral sex). It’s incredibly rare to pass genital HSV-2 to your partners mouth through oral sex (only 1% of HSV-2 cases are oral). And just to be totally clear, herpes CANNOT be transmitted by sharing a towel or drinking after someone! In short, there must be an opening in the receiver’s body for the herpes virus to gain access, whether that be a mucous membrane or a small cut/abrasion in the skin (which is why bikini waxing has been all over the news as making you more prone to getting herpes).
So now that you understand those basics of how herpes actually gets from one body into another (and how it doesn’t), here are the chances of transmitting herpes to a partner:
Female to male transmission rates are 4%*
Male to female transmission rates are 10%*
When condoms are used, both of the rates above decrease by half (2% and 5%, respectively) and suppressive therapy has that fall by another half
*when no protection is used and sex is avoided during active outbreaks