How can I avoid catching an STI/STD from having sex?
The only 100% effective way to avoid getting an STD is by not having sex or sexual contact. And let's be honest for many of us that's not going to happen... your next best bet is to practice safe sex - using either a male or female condom and/or dental dam every time, getting tested regularly and asking anyone you are getting physical with to do the same.
STIs/STDs can't just come from nowhere. There is risk only when one person already has an STI/STD. And since most STIs/STDs don’t have symptoms, you can’t rely on what you see to tell you whether or not an infection is present. Play safe! Stay Safe!