A number of disorders can affect the ability to have or enjoy sex, including erectile dysfunction and female sexual problems. Concerns about infertility or fear of unplanned pregnancy can also come into play.
In addition, a number of diseases and disorders affect sexual health. These include sexually transmitted diseases and cancer. In men, treatment of prostate cancer can cause erectile dysfunction. In women, cervical, uterine, vaginal, vulvar or ovarian cancer may have sexual effects.
MedlinePlus - Sexual Health