Before for sure. Wife would rather have a clean cock to suck. As far as afterwards, I usually don't and wife doesn't either unless I shoot my load on her, then she does
Yeh, always clean to start with but even if we're covered in goo later, we stay like that until morning and then, usually, would have more fun before later having a shower or bath together. I've often wondered if things like thrush are caused or made worse by guys shoving a grubby cock inside her. Perhaps other conditions too?
If you don't use a condom, cleaning before and or after will do nothing to prevent getting an STI from fluid transmission. You're right, someone that is physically clean can still be carrying and transmitting diseases. I would have to say that while all sex can disrupt the PH of the vagina and increase the susceptibility to an increase of yeast production, otherwise known as a yeast infection, thrush, jock itch, etc... I would imagine that introducing extra "grubby" stuff would only compound the problem. To avoid yeast infections and UTIs which are not considered STI/STD but do often happen in conjunction with sex, it is advisable to clean up afterwards, before as well if either party are "grubby." If you have good hygiene and haven't been sweating or doing anything that would make you filthy since taking a shower, cleaning before sex is not necessary.
You can indeed catch an infection from a dirty cock. Doesn't necessarily mean an STI but, as others have mentioned,it can be a UTI and it could mean others. I saw a program on TV within the past month, which mentioned other internal issues that can really affect women when inserting dirty things into their vagina. They actually stated, 'anything dirty whether that's a toy or a penis'. I always clean beforehand not just out of respect for her but, if I am to go down on her, I prefer her to be clean and nice-smelling. What's good for the goose etc.
I take a morning shower everyday. Before sex, it varies. Sometimes she wants to sense my body odor. It isn't that it reeks but people have a natural scent. I've had partners that enjoy mine. Bathing removes the oils that provide the scent. But there are other times that I'm to odiferous and really need to shower off. After having sex I never shower right away. Piss? Yes. Shower? Not often. I love having the smell of sex on my body. Now, one of the best ways to avoid UTI's is urinating directly after. I usually have a full bladder after the exertion of fucking so pissing is required. STI's are prevented by the use of condoms. I use them with new partners if either I or she feel the need. Otherwise not.
Wife & I shower before sex all the time. Honestly there are times when I’m not smelling my best, I would hate for to go down on me and get a whiff of something bad - or vice versa. It just feels better to be all clean and not have to worry about that. We enjoy being naked so we’re in the habit of making sure that we’re clean as we need to be.
Sometimes I think I read too much, or I'm just getting old. It's getting harder to remember who wrote what, when and where. However ... One of the Authors I read, wrote; "The powers that be want you to believe that sex is a dirty thing. Hogwash! Sex is only dirty if you don't wash yourself." Of course Woody Allen disagrees, he says "Sex is only dirty if you're doing it right." Yes, Clean up before sex, and after sex. And if you are so inclined, During Sex. Many of the women I dated in the past really enjoyed sex in the shower, in the bathtub, in a pool or hot tub. They just liked sex in water.
My wife insists on both of us showering before anything. The thing is, she does nothing more now than suck and pull me off, and use her stretching devices (she has vaginismus). She covers the entire bed with towels, and one on the floor near my side. Oh to make enough mess to justify the towels. My first wife never thought to use a towel under her butt. I'd pump her full of come and she'd complain about the wet patch.