18 Flee from fornication! Every sin that a man may commit is outside the body, but he who fornicates sins against his own body.*Precisely. Verse 16 above states plainly that whoever joins himself to a prostitute becomes one flesh with her. "The two will become one flesh" is not a poetic expression; it is a medical fact. During coitus there is an exchange of enzymes, such that the participants are affected in their bodies, literally. It follows that a promiscuous person is damaging his body, progressively. But it may be worse even than that. Proverbs 6:32 says: "Whoever commits adultery with a woman lacks understanding; he who does so destroys his own soul." Verses 33-35 describe the social consequences, but I believe the participants suffer consequences within themselves as well. I suspect that along with the enzymes goes a bit of the soul, so a professional prostitute has a seriously weakened soul, and a promiscuous male keeps on lousing up his soul, quite apart from the physical consequences. No wonder the Text says to flee!!