Board Thread:Questions and Answers/@comment-104.172.189.120-20150505044206/@comment-1512833-20160907025457

In Tokyo Ghoul, the race known as ghouls just is. It's as if you'd ask "how do you become a human". They are just born from other ghouls. No magic, no virus, no experiment. The only way for a human to become a ghoul is to undergo a torturous transplant of ghoul organs into a human body, which was, until the beginning of the manga, considered an impossibility.

So in short, unless Kanou gets your hands on you or you are part of the CCG, you do not become a ghoul, period.