Short answers, pulled from the story.
Oral sex carries a lower risk of sexually transmitted infection than vaginal or anal sex, with HIV transmission considered the lowest risk. However, infections including Chlamydia and human papillomavirus (HPV) can still be transmitted orally. Barrier methods such as condoms for fellatio or dental dams for cunnilingus reduce risk when a partner's STI status is unknown.
Research has linked unprotected oral sex with HPV-positive partners to increased oral and throat cancer risk. A 2005 study at Malmö University found HPV in 36 percent of oral cancer patients versus only 1 percent of healthy controls. A study in The New England Journal of Medicine found that people with more than five oral sex partners had a 250 percent increased risk of throat cancer compared with those who never engaged in the practice.
Oral sex alone cannot result in pregnancy because the human gastrointestinal system has no connection to the reproductive system, and swallowed sperm is destroyed by stomach acids. A residual risk exists only if semen contacts the vaginal area indirectly, such as via fingers or hands.
A 2005 National Center for Health Statistics report, drawn from a computer-administered survey of more than 12,000 Americans aged 15 to 44, found that over half of the teenagers surveyed had experienced oral sex. The Centers for Disease Control and Prevention confirmed in 2009 that oral sex is commonly practiced among adolescents of various sexual orientations.
Ancient Rome considered fellatio profoundly shameful for the giver, who was seen as the submissive party. Known practitioners were believed to have foul breath and were often excluded from dinner tables. Chinese Taoism, by contrast, regards cunnilingus as a spiritually fulfilling act believed to enhance longevity.
Research suggests fellatio may reduce miscarriage risk through a process called paternal tolerance, in which repeated exposure to proteins in a partner's semen helps establish the mother's immunological acceptance of the pregnancy. Researchers noted that the data overwhelmingly supports the theory that repeated semen exposure establishes the maternal immunological tolerance necessary for a safe and successful pregnancy.