Hello
Yes, you're correct. Any time you introduce different bacteria to the vaginal environment, there is a risk of bacterial infection or yeast infection. This can be achieved through vaginal or anal intercourse, manual sex, shared sex toys, vaginal intercourse wearing a condom that was also used for anal intercourse.
Your girlfriend can try an over-the-counter medication for infection, such as Vagisil, or see her gynecologist for prescription-strength antiobiotics such as Metronidazole (Flagyl) or clindamycin if her symptoms are extreme.
And, please, in addition to washing your penis, you should ALWAYS use a condom for any insertive sexual activities such as penis-vagina or penis-anus.
If you decide to try penis-anus sex again, here's some important guidelines for you:
Many people greatly enjoy anal stimulation—whether with a tongue, finger, penis or dildo. This is a sexual activity that requires lots of good technique and communication.
The anus is a very tight orifice, and many people experience pain with deep penetration, no matter what kind of technique they use.
The keys to anal sex are 1) lots of lube (the anus doesn’t produce its own lubrication), 2) lots of stimulation of the anal area (to relax that tight sphincter) and 3) gentle, slow penetration, not just ramming it in. Start gradually and slowly, first with just a finger, and then if you mutually decide on penis insertion, do that very slowly as well. It’s OK if your girlfriend discovers that she only want to be penetrated by something small, rather than something a bit more “important” like a penis. Be sure the two of you are communicating during anal sex; she should tell you if she experiences pain and or if something doesn't feel good so that you can stop or go slower. And for many people, it only feels good up to 3 inches or so. Many people find deep penetration painful, but enjoy shallow penetration with a finger or other small object.
Very important: The anus is a very tight orifice, and tears easily, leaving it vulnerable to infection, so BE SURE to use a condom. And, again, don't put anything in the vagina that has first been in the anus (fingers, toys, penises, etc.) without using a new condom, because the bacteria that live in the anus can be harmful to the vaginal environment, which can cause various unpleasant side effects like yeast infections. Dr. J
Thank you so much for such a quick reply, this is really helpfull. I took down the medication you gave me, although she does not have any symptoms, and she seems fine at the moment... should I take precausions and advise her to take some vagisil just incase?