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Overview of Sexually Transmitted Infections


The Manual's Editorial Staff

Reviewed/Revised Apr 2023
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What are sexual transmitted infections (STIs)?

STIs are infections that are passed from person to person through sexual contact, including oral sex.

Pathway From the Vagina to the Ovaries

In women, some organisms can enter the vagina and infect other reproductive organs. From the vagina, these organisms can enter the cervix and uterus and may reach the fallopian tubes and sometimes the ovaries.

Internal Female Genital Organs

Pathway From the Penis to the Epididymis

Occasionally in men, organisms spread up the urethra and travel through the tube that carries sperm from the testis (vas deferens) to infect the epididymis at the top of a testis.

Male Reproductive Organs

What causes STIs?

STIs are caused by tiny viruses, bacteria, and parasites, depending on the disease. People who have sex with an infected partner can get an STI. The sex can be vaginal, oral, or anal. However, some STIs also can be spread in other ways, including:

  • Kissing or close body contact

  • From mother to child before or during birth

  • Breastfeeding

What are the symptoms of STIs?

Some STIs do not cause symptoms. If you do have symptoms of an STI, you may have:

  • Sores on your genitals or mouth

  • Discharge from the sores or your genitals

  • Pain or itching

  • Pain when urinating (peeing)

If you don't get treated quickly, some STIs can cause more serious problems:

  • Heart and brain infections

  • Cancer

  • Infertility (when you can't get pregnant)

How can doctors tell if I have an STI?

Doctors may do tests on your blood, urine, or on a sample from your penis, vagina, throat, or rectum.

If you have one STI, doctors also do tests for other STIs—people who have one STI have a relatively high chance of having another one.

How can I prevent STIs?

Practice safe sex

  • Use condoms correctly every time you have sex

  • Avoid having lots of sex partners

  • Avoid having sex with people who engage in sex work

  • Male circumcision (surgery to remove the foreskin from the penis) helps reduce the spread of HIV from women to men

How to Use a Condom

  • Use a new condom for each act of sexual intercourse.

  • Use the correct size condom.

  • Carefully handle the condom to avoid damaging it with fingernails, teeth, or other sharp objects.

  • Put the condom on after the penis is erect and before any genital contact with the partner.

  • Determine which way the condom is rolled by placing it on the index finger and gently trying to unroll it, but only a little bit. If it resists, turn it over, and try the other way. Then reroll it.

  • Place the rolled condom over the tip of the erect penis.

  • Leave 1/2 inch at the tip of the condom to collect semen.

  • With one hand, squeeze trapped air out of the tip of the condom.

  • If uncircumcised, pull the foreskin back before unrolling the condom.

  • With the other hand, roll the condom over the penis to its base and smooth out any air bubbles.

  • Make sure that lubrication is adequate during intercourse.

  • With latex condoms, use only water-based lubricants. Oil-based lubricants (such as petroleum jelly, shortening, mineral oil, massage oils, body lotions, and cooking oil) can weaken latex and cause the condom to break.

  • Hold the condom firmly against the base of the penis during withdrawal, and withdraw the penis while it is still erect to prevent slippage.

Get vaccines (shots)

How do doctors treat STIs?

Most STIs can be treated with medicines. Some viral STIs can't be cured, so you have them for life.

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