How safe is frottage -- specifically cock rubbing along the buttcrack -- when the head of the penis doesn't graze or enter the anus? I read an article about frottage that suggested if you cockrub the ass, you should wear a condom. Is there a different risk if you cum on the guy's back while doing it? Is it still too close to the anus to do it unprotected?
Certain infections like syphilis or herpes can be transmitted through frottage as you describe, but other infections like HIV, chlamydia or gonorrhea would be extremely unlikely. Generally, frottage is considered a safer sex activity, cum or no cum.
To your health,