Becoming sexually active at a young age.

Having many sexual partners or partners who have had multiple partners.

Smoking.

Infection with a high-risk strain of human papillomavirus (HPV).

Infection with genital herpes or chronic chlamydia.

A weakened immune system because of factors such as HIV infection or medication that suppresses the immune system.

Prenatal exposure to an estrogen drug called DES (diethylstilbestrol).

Low socioeconomic status and resulting lack of access to medical care.

—P.E.R.