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.
Genital warts are a very common sexually transmitted infection. They are caused by the Human papillomavirus (HPV). There are many different types of HPV. Some types cause visible genital warts (usually types 6 and 11).