Oral sex is the X-rated culprit behind a wave of throat cancer cropping up in the US, fueling a so-called “epidemic.” According to Hisham Mehanna, a professor at the Institute of Cancer and Genomic Sciences at the University of Birmingham, the human papillomavirus is to blame. “For oropharyngeal cancer, the main risk factor is the number of lifetime sexual partners, especially oral sex,” he wrote for the Conversation Tuesday.