What Causes STIs? | Family Planning

Several types of organisms cause STIs. Those caused by bacteria or parasites can generally be cured. STIs caused by viruses generally cannot be cured, although they can be treated to relieve or eliminate symptoms. Most STIs are spread by sexual activity, and much of this spread can be prevented by the correct and consistent use of condoms. Some people, however, can get an STI in other ways. Details are provided in the table below.

STI Types, Causes, Cures, and How They Are Spread

STI	Type	Sexual spread	Nonsexual spread	Curable?
Chancroid	Bacterial	Vaginal, anal, and oral sex	None	Yes
Chlamydia	Bacterial	Vaginal and anal sex rarely, from genitals to mouth	From mother to child during delivery	Yes
Gonorrhea	Bacterial	Vaginal and anal sex, or contact between mouth and genitals	From mother to child during delivery, or through breast milk Contaminated blood transfusion	Yes
Hepatitis B	Viral	Vaginal and anal sex, or from penis to mouth	From mother to child during delivery, or through breast milk Contaminated blood transfusion	No
Herpes	Viral	Genital or oral contact with an ulcer, including during vaginal and anal sex; also genital contact in area without ulcer	From mother to child during pregnancy or delivery	No
HIV	Viral	Vaginal and anal sex, or very rarely, oral sex	From mother to child during delivery, or through breast milk Injection drug use with nonsterile needles Contaminated blood transfusion	No
Human papillomavirus (HPV)	Viral	Vaginal, anal, and oral sex	From mother to child during delivery	No
Human T-lymphotropic virus	Viral	Vaginal and anal sex	From mother to child during delivery, or through breast milk Contaminated blood transfusion	No
Syphilis	Bacterial	Genital or oral contact with an ulcer, including vaginal and anal sex	From mother to child during delivery, or through breast milk Contaminated blood transfusion	Yes
Trichomoniasis	Parasitic	Vaginal, anal, and oral sex	From mother to child during delivery	Yes