As far as Normal Vaginal sex is concerned, it will not cause any harm in terms of internal organ damage. But yes there are merits and demerits of everything. Merits of Sex from Back. Deep Penetrations Greater Satisfaction level Demerits: increase chance of infection from anal region to husband because it comes in direct contact. increase chance of vaginal infection as it can more easily transfer from anus to vagina during sex So increased chance of STD. Somewhat Decrease the chance of getting pregnant as compared to normal because it accumulate semen on the opposite direction. You can decrese this chance of infectino if you use protection (Condom) during sex. Maintain proper hygiene. Do wast and clean anal and perianal region before sex. And of course if you try with some other position in which you avoid direct contact with anal region.