You know I had that same question. I think it is safe to swallow semen. I learned that herpes doesn't live in the cum and i don't think hiv is transmitted this way. Let's google it shall we? I just read a little bit of peoples answers and they say as long as he doesn't have any disease. You got to remember a lot of this stuff is "theory" too. Nobody really knows 100% good answer. So if you're with someone monogomously and you know they've been tested for everything, without sleeping with someone else then go for it.