Use a comma to separate nonessential elements from a sentence. More specifically, when a sentence includes information that is not crucial to the message or intent of the sentence, enclose it in or separate it by commas.
Genital warts are a sexually transmitted infection (STI) caused by certain strains of the human papillomavirus (HPV). These skin growths can cause pain, discomfort, and itching. They are especially dangerous for women because some types of HPV can also cause cancer of the cervix and vulva.
1 Genital warts are caused by the human papillomavirus (HPV). 2  Genital warts affect both women and men, but women are more vulnerable to complications.  Genital warts can be treated, but they can come back unless the underlying infection is also treated.