STDs are transmittable diseases--they're infections. They cannot be "created" or "formed," only passed on. Having said that, a horrifying number of sexually active people are infected with STDs and don't know it. Many sexually transmitted infections, as we're now calling them, are asymptomatic for a period of time before they cause obvious problems. More worrisome is that the majority of these infections can cause infertility in women and girls before they even know they have the infection. While many of these infections are curable or treatable, the infertility is not. Unprotected sex is NOT worth the risk unless you're in a committed relationship in which all partners have been tested and are truly only having sex with each other. Even then, people lie.