In the 70s, there were only 2 commonly known sexually transmitted diseases/infections (STIs). There are currently at least 30 STIs.  The ten most common STIs are chlamydia, gonorrhea, syphilis, HIV/Aids, hepatitis B, genital herpes, HPV, trichomoniasis, crabs, and mycoplasma genitalium. 

What causes STIs?

STIs can be caused by bacteria (e.g., chlamydia, gonorrhea, syphilis), viruses (e.g., HIV/Aids, hepatitis B, genital herpes, HPV) or parasites (trichomoniasis). 

How do you get an STI?

STIs are acquired during sexual activity.  This includes vaginal sex, oral sex, and anal sex.  A few, such as syphilis, HPV, and herpes, can even be spread by contact with infected skin.  Others, such as HIV and hepatitis, can also be spread through needle-sharing.  An STI can be acquired from someone who has no symptoms.

What are the symptoms?

Most people with STIs have no symptoms. Even without symptoms, a person can pass on his/her STI infection. Some STIs cause symptoms such as abnormal discharge from the penis or vagina, a burning sensation when urinating, and abdominal pain. Skin changes can also occur, such as rashes, ulcers, and warts.

What are the complications?

Complications from an STI infection include pelvic inflammatory disease (PID) leading to infertility and possible tubal pregnancy. In pregnant women, STIs can lead to miscarriage, stillbirths, preterm delivery, and birth defects. A mother infected with a herpes virus can transmit the virus to her baby during the birth if the virus is active at that time. Every year in the U.S. over 30,000 women and men are diagnosed with a cancer caused by HPV infections, including cervical, anal and oral cancers. 

How can you find out if you have an STI? 

Since most STIs cause no symptoms, they are often not detected until complications develop. However, most STIs can be diagnosed with blood tests.  Some require a swab for diagnosis. Talk to your doctor about getting screened. 

Can STIs be treated?

Most bacterial STIs can be treated and cured with antibodies. Treatment does not guarantee that complications will not occur later. A few viral STIs can be treated and occasionally cured like hepatitis B and C.  However, other viral STIs can only be treated for symptoms but not cured (such as HIV and herpes).


Vaccination for hepatitis B is effective. Vaccination for HPV is also available and recommended for young people before they become sexually active. The latest HPV vaccine protects against 9 different HPV viruses (including the 2 types that cause most cancers). However, vaccinations for HPV and Hepatitis B&C will not protect someone who has already acquired those STIs.

Can STIs be prevented?

The consistent and correct use of condoms use can reduce the risk of getting an STI. However, according to the CDC, condoms do not offer complete protection against STIs. Please see our Research Topic covering “Condoms”. The CDC states “[t]he most reliable ways to avoid transmission of STDs are to abstain from sexual activity, or to be in a long-term mutually monogamous relationship with an uninfected partner.i

for further reading

Website Resources

Scroll to top