It is something that is completely mentally. Simply set your mind to not doing it, and that is will eventually be the cause of you getting sick, if it hasn't in the past already. It's unhealthy, and disgusting. I did it for a while when I was a kid, and tried alot of things to quit, nothing worked until I personally said that I was done, and didn't do it again. It is basically like smoking cigarettes there is no benefit it's just an addiction, which is completely in your head. Nothing will ever assist you in quitting something besides yourself. Stand strong, and simply don't do it again.