All research that involves human subjects requires ethical review. For example, one of the most infamous examples of a study concerned with human sexuality was the Tuskegee experiment, in which black men with syphilis were left without treatment and just observed so that doctors could learn more about the course of the disease. In response to the ensuing scandal, President Clinton apologized to the victims and established the Tuskegee University’s National Center for Bioethics in Research and Health Care. In an earlier experiment, US researchers in Guatemala deliberately infected people with syphilis so that they could study the disease—something also ethically problematic.
Another issue involves studying young people. For example, even if the study is just a written survey, researchers must balance the importance of confidentiality with the need to protect children who might be engaged in risky behavior. Also, when dealing with minors, parental consent is always needed, but many adolescents might not be comfortable with speaking freely when parents are involved in any way. Also, on the subject of privacy, as there is still prejudice against many LGBTQ people and, to a different extent, those who are involved in the BDSM community, an important ethical issue is ensuring privacy. Privacy also becomes a problem when studying pedophiles, as the need for accurate information conflicts with the need to report pedophiles and protect children.
In the case of studying STDs, there is a question also about confidentiality. Patients might only agree to be studied or treated if information is kept in confidence, but researchers might also feel an obligation to inform or warn people who might be infected by the person with an STD engaging in unprotected sexual activities.