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.
They are not cancerous. Warts are caused by infection with a type of human papillomavirus (HPV). Factors that increase the risk include use of public showers, working with meat, eczema, and a low immune system. The virus is believed to enter the body through skin that has been damaged slightly.