KARACHI, Pakistan — You can’t go a day on the streets of Pakistan without hearing some spectacularly rude words and colorful insults taken in stride, whether thrown in anger at an errant motorist or in banter among friends at a tea shop. But the words “sex education” are different; they release a tirade of moral righteousness from many Pakistanis, who find this the dirtiest phrase of all. These people fear that it means “teaching children how to have sex,” rather than educating them about their health and reproductive rights.

At least in some parts of Pakistan, though, that is beginning to change.

Most Pakistanis still profess conservatism and modesty about sexual relations and matters of the body. But Dr. Nafis Sadik, a United Nations population expert who led Pakistan’s successful Family Planning Program in the 1960s, describes a deeper feeling of fear: that if girls are given access to information about sexual health and reproduction, they will become promiscuous. “Boys’ and men’s sexual behavior is condoned and appreciated,” she has said, “but girls’ and women’s sexual behavior is seen as something that needs to be controlled.”

Nevertheless, attitudes are evolving — not least because this prudishness has proved dangerous for the nation.

Today, Pakistanis face a major health care crisis of deadly communicable diseases like hepatitis C, which is rampant in rural areas, as well as a flood of health problems that women and girls experience because Pakistan has also retained the practice of early marriage. Many girls are married off by their families as soon as — or even shortly before — they have reached puberty in their early teens. A result: Pakistan ranks near the bottom among countries in maternal and child health care.