Sexually Transmitted Infections (STIs)

Overview

Sexually transmitted infections (STIs) are a group of illnesses passed from person to person through sexual contact. They spread through intimate sexual contact involving the penis, vagina, mouth, anus, or contact with any of the membranes that line the urinary and/or genital tracts.

Healthcare providers often use the word “infection” instead of “disease” because a person can have an STI with no symptoms but still need treatment. When left untreated, an STI can become a disease.

STIs affect men and women of all races, backgrounds, sexual orientations, and economic levels. Anyone who has vaginal, anal, or oral sex could get an STI. STIs have a significant impact on adults and infants (who may contract an STI during pregnancy or delivery) and affect millions of people in the United States every year.

Signs and Symptoms

Many people with STIs have no symptoms at all. Even without symptoms, a person can still pass an STI to others.

When symptoms do appear, they may include, but are not limited to:

• Unusual discharge from the penis or vagina
• Sores or warts on the genital or anal area
• Painful or frequent urination
• Itching and redness in the genital area
• Blisters or sores in or around the mouth
• Abnormal vaginal odor
• Anal itching, soreness, sores, discharge or bleeding
• Abdominal pain
• Fever

Symptoms can vary depending on the specific STI. Over time, symptoms may improve on their own, but the infection may still be there and require treatment.

Signs and Symptoms of Specific STIs

Bacterial Vaginosis

This syndrome results from an imbalance in the vaginal microbiome, the mix of beneficial and harmful bacteria typically present in the vagina. The most common symptom is a thin, milky discharge that often has a “fishy” odor. Some women have no symptoms. Bacterial vaginosis increases the chances of getting HIV and other STIs even if a woman does not have symptoms. If untreated, this condition can cause preterm labor and birth, low birth weight, and pelvic inflammatory disease.

Candidiasis

Overgrowth of fungi called Candida in the vagina can cause symptoms to develop. Candidiasis in the vagina is typically called a “yeast infection.” For people with certain risk factors, Candida overgrowth can cause invasive candidiasis, a serious infection that can affect the blood, heart, brain, eyes, bones and other parts of the body.

Chlamydia

Chlamydia can cause inflammation of the cervix in women and inflammation of the urethra and the lining of the rectum in both men and women. Many people with chlamydia have no symptoms. When symptoms occur, they can include fever, abdominal pain, and unusual discharge from the penis, vagina, or anus.

If left untreated, 10-20% of chlamydial infections in women can result in pelvic inflammatory disease. Pelvic inflammatory disease can cause scarring on women’s reproductive organs. The scarring can lead to infertility, ectopic pregnancy, chronic pelvic pain, abscesses, and other serious problems. If a pregnant woman has chlamydia, it can pass to the fetus during pregnancy or to the baby during delivery. If a woman passes it to her baby during birth, the baby may get eye infections or pneumonia.

In men, untreated chlamydia may cause urethritis, epididymitis, acute prostatitis, proctitis, and pharyngitis.

Gonorrhea

Gonorrhea is caused by bacteria that infect the reproductive tract, including the cervix, uterus, and fallopian tubes in women, and the urethra in women and men. The bacteria can also establish infection in the mouth, throat, eyes, and rectum. The most common symptoms are discharge from the vagina or penis and painful or difficult urination.

In women, untreated gonorrhea can cause pelvic inflammatory disease, ectopic pregnancy, and infertility. In both men and women, gonorrhea can cause infections in the mouth, throat, eyes, and rectum. It also can spread to the blood and joints; if this happens, it can become life-threatening. People with gonorrhea can get HIV more easily than people who do not have gonorrhea. In men, untreated gonorrhea may cause epididymitis, a painful infection in the tissue surrounding the testicles, urethritis, an infection of the urinary canal in the penis, acute prostatitis, and pharyngitis.

Viral hepatitis 

Viral hepatitis is an inflammatory liver disease caused by infection with any of the known hepatitis viruses—A, B, C, D and E. Hepatitis A, B and C can be sexually transmitted.

Herpes

Herpes is caused by two types of a virus called herpes simplex virus. Herpes simplex virus type 1 usually appears as fever blisters or cold sores on the lips, but it can affect the genital area. Herpes simplex virus type 2 typically causes painful, watery skin blisters on or around the genitals or anus. Many with herpes do not have any symptoms or have only minimal symptoms. Some people experience periodic outbreaks when new blisters form. The virus is more likely to pass to others during an outbreak.

In severe cases, herpes can lead to life-threatening or long-term complications, typically in the central nervous system. Herpes is a leading cause of viral encephalitis, brain inflammation from a viral infection, and infectious blindness. Pregnant women who get genital herpes for the first time during pregnancy may pass it to their newborns. This can lead to life-threatening neonatal herpes in babies that can affect their skin, brain, and other organs. If untreated, neonatal herpes is fatal in 60% of cases.

Human Immunodeficiency Virus (HIV)

HIV is a virus that attacks the body’s immune system and destroys blood cells that are important for fighting infections and diseases. This damage leaves people with HIV more vulnerable to other infections and illnesses. Some people with HIV may not have symptoms, but they can transmit the virus to others as early as two weeks after infection. If HIV is left untreated, it can lead to AIDS.

Antiretroviral therapy (ART) reduces the amount of HIV in the blood but does not cure HIV infection. ART is recommended for everyone with HIV to help support a long, healthy life. When taken consistently, ART can reduce the chances of HIV transmission through sex to zero and less than 1 percent while breastfeeding; untreated HIV is more likely to be spread through sex, needle sharing, pregnancy, and breastfeeding.

Human Papillomavirus (HPV)

HPV is a large family of viruses that infects the skin and the moist surfaces of the body, such as the mouth and genital areas. HPV affects special cells which build the barrier protecting the surfaces of the body called keratinocytes, causing them to grow more than normal. This can lead to different medical conditions. Some are uncomfortable but benign, like common skin or genital warts. Others can cause early cell changes (called precancerous lesions), and in some cases, these changes can develop into cancer.

There are many types of HPV. Some are “low-risk” types and mainly cause genital warts, while others are defined “high-risk” and can lead to more serious precancerous changes in cells. If these changes are not found and treated early, they can turn into cancers of the cervix, vagina, vulva, penis, anus, nose, mouth, or throat.

People with weakened immune systems, such as those living with HIV or other condition or drugs that impair the immune system, are more likely to develop HPV-related diseases, including warts, precancerous changes, and cancers, compared to people with healthy immune systems.

Mpox

People who acquire Mpox (Monkeypox virus) tend to clear the infection on their own, but the virus can cause serious disease in children, pregnant women, and other people with compromised immune systems, including people with HIV. Initial symptoms of mpox include fever, headache and body aches, fatigue, and swollen lymph nodes, followed by a rash affecting the skin and often mouth or genital area. Rare but serious complications of mpox include dehydration, bacterial infections, pneumonia, brain inflammation, sepsis, eye infections, and death.

Syphilis

The first sign of syphilis is a chancre, a painless genital sore that most often appears on the penis or in and around the vagina. Chancres typically go away on their own, but the infection still requires treatment to go away. Other sores, such as a syphilis rash, can appear in later stages. Syphilis chancres, or painless genital sores, make a person 2-5 times more likely to get HIV.

Without treatment, syphilis can spread to and damage many organs, including the skin, heart, blood vessels, liver, bones, and joints. In its tertiary stage, it can also affect the nerves, eyes, and brain, and may be fatal. In pregnant women, untreated syphilis increases the risk of miscarriage and stillbirth. Babies who contract syphilis in the womb may suffer from a range of serious complications, including misshapen bones, severe anemia, enlarged liver and spleen, jaundice, meningitis, skin rashes, and neurological problems such as blindness or deafness.

Trichomoniasis

This infection can cause frequent, painful, or “burning” urination in men and women. In women, it can also cause vaginal discharge, genital soreness, redness, or itching. It may also cause no symptoms, so a person may not know they have it.

Women who have trichomoniasis during pregnancy have higher chances of preterm labor or birth and having babies with low birth weight. Stillbirth and newborn death are more than twice as likely in pregnant women with trichomoniasis. Trichomoniasis can also increase the possibility of getting or spreading other STIs.

Zika Virus

Zika is usually mild, with symptoms lasting for several days to one week. Women who get Zika during pregnancy may transmit the virus to the fetus, which can result in very serious birth defects, including microcephaly (unusually small head).

Related Health Effects

STIs can cause serious, long-term health problems, especially in women and babies. In rare cases, STIs can lead to serious illness or death.

A person with an STI is 2-5 times more likely than someone without an STI to get HIV when exposed to HIV through sexual contact. If a person already has HIV, having another STI increases the chances they will pass HIV to their sexual partner.

Women who have an STI during pregnancy may experience:

• Miscarriage (fetal loss before 20 weeks)
• Ectopic pregnancy (when the embryo implants outside of the uterus, usually in a fallopian tube)
• Preterm labor and delivery (before 37 weeks of pregnancy)
• Low birth weight
• Congenital anomalies, including blindness, microcephaly, deafness, bone deformities, and intellectual disability
• Stillbirth (fetal loss at or after 20 weeks)
• Illness during the first month of life
• Newborn death

Causes and Risk Factors

There are three major causes of STIs:

• Bacteria, including chlamydia, gonorrhea, and syphilis
  • Bacterial Vaginosis (BV),a common vaginal condition, occurs when bacteria that normally are present in small amounts increase and replace normal vaginal bacteria. BV can occur without sexual activity, but factors like douching, not using condoms, and having new or multiple sex partners increase the risk. BV can increase the risk of other sexually transmitted infections (STIs) and complications during pregnancy.
• Viruses, including HIV, herpes, human papilloma virus, hepatitis viruses, cytomegalovirus, Mpox, and Zika
• Parasites, such as Trichomonas vaginalis, or insects such as crab lice or scabies mites

Any STI can spread through sexual activity, including sexual intercourse. Some STIs also spread through oral sex and other sexual activity. Ejaculation does not have to occur for an STI to pass from person to person. Once a person has an STI, they can pass it other people through oral, vaginal, or anal sex, even if they have no symptoms.

Prevention Guidance

Sexual abstinence, or not having vaginal, anal, or oral sex, is the only way to fully eliminate the chance of getting an STI. But there are steps you can take to lower your chances of getting an STI.

Safer Sex Practices

• Use condoms correctly every time you have sex.
• Limit your number of sex partners.
• Do not drink alcohol or use drugs before or during sex.
• Only have sex with people who get tested regularly.
• Ask your sex partners about their STI and health history.

Condoms lower chance of getting certain STIs, but they cannot prevent every STI. Viruses and some bacteria can pass from person to person by skin-to-skin contact in the genital area that is not covered by a condom.

Get Vaccinated

Vaccines are available for certain STIs:

• HPV vaccine: There are two vaccines that protect against most, but not all, HPV types that cause cervical cancer. A group advising the Centers for Disease Control and Prevention, or CDC, recommends this vaccine for boys and girls starting at age 11 or 12. The CDC recommends that people with HIV, starting at age 9, receive the HPV vaccine. People with HIV usually receive three doses of the vaccine over a 6-month period.
• Hepatitis A vaccine: Vaccination can prevent hepatitis A.
• Hepatitis B vaccine: Vaccination can prevent hepatitis B. For pregnant women with hepatitis B, a series of vaccinations during pregnancy and a vaccine for the baby at birth can prevent the baby from getting hepatitis B during birth.
• Mpox vaccine: Vaccines are available for preventing mpox.

Get Tested Regularly

For people who have sex regularly with more than one partner, the best way to identify and treat STIs is to get tested regularly. Talk to your healthcare provider about how often you should be tested.

Prevention During Pregnancy

Pregnant women should take special steps to protect themselves and their babies:

• HIV treatment during pregnancy can prevent women with HIV from passing the virus to the baby.
• If a woman has active herpes lesions or untreated HIV, a caesarean delivery, also called a c-section, can prevent transmission to the baby.
• In most hospitals, babies’ eyes are treated with antibiotic ointment shortly after birth to prevent blindness from exposure to gonorrhea or chlamydia during delivery.
• Women who are pregnant or thinking about getting pregnant are advised not to travel to areas where Zika has been reported.

Diagnosis

Any person who is sexually active should discuss their chances of getting an STI with a healthcare provider and ask about getting tested. Many STIs do not cause symptoms, so a person may have an STI and not know it.

If you have an STI, it is important to start treatment to prevent passing the STI to other people and to lower the chances of long-term complications. Recent sexual partners should also be tested and, if necessary, treated to prevent re-infection and further transmission.

Diagnosing STIs

Most STIs are diagnosed during a physical exam and DNA analysis of fluid swabbed from the vagina, penis, or anus. DNA testing can take several days, however the ability to get results while the patient is in the doctor’s office is becoming more common.

The effects of HPV, which causes genital warts and cervical cancer, can be detected through a Pap test, which checks cells from the cervix for abnormal changes.

Blood tests detect infections like HIV, hepatitis A, B, and C, herpes and syphilis.

Many healthcare providers diagnose and treat STIs based on the symptoms a person describes. This approach can result in inadequate treatment.

Screening During Pregnancy

It is important for pregnant women to get screened for STIs during an early prenatal medical visit. Many STIs can pass to the fetus during pregnancy or to the baby during delivery. Even if the STI is not curable, there are steps women can take to protect the baby.

Health Department Notification

Because STIs are passed from person to person and can have serious health consequences, state and local health departments may notify people who have been exposed to certain STIs. If you receive notice, it is important to see a healthcare provider, get tested, and start treatment right away.

Treatment and Management

Antibiotics can treat STIs that are caused by bacteria or parasites. These antibiotics are most often taken by mouth but sometimes are injected or applied directly to the affected area.

There is no cure for STIs that are caused by viruses, but treatment can relieve or eliminate symptoms and help keep the STI under control. Treatments for viral STIs also can reduce or eliminate the chance of passing the STI to a partner.

It is important that the person with the STI and their partner(s) take all medicine prescribed by their healthcare provider to ensure the STI is completely treated. They should follow their healthcare provider’s recommendations on how long to abstain from sex after treatment is completed.

Living With STIs

In the case of STIs caused by viruses with no cure, such as HIV, genital herpes, or hepatitis, special care, treatment, and preventive measures can help control the infection, limit symptoms, maximize health and prevent spreading the virus to sexual partners.

You should see your healthcare provider for treatment as soon as possible after receiving a diagnosis of an STI. You should also notify all recent sex partners and advise them to see their healthcare providers and be treated. These steps will reduce the chances of reinfection, help avoid spreading the STI to other people, and decrease the odds that your previous sexual partners will develop serious complications.

You and all your sex partners must avoid sex until treatment is complete, or, for HIV, has reduced the amount of virus in your body to an undetectable level, and all symptoms have disappeared.

Find Clinical Trials

Clinical trials uncover better ways to prevent, diagnose, treat, and understand diseases and conditions. To ensure results apply to everyone, volunteers of all ages, sexes, and backgrounds, including both healthy individuals and those with specific medical conditions, are needed. Find clinical trials on STI.

Find Treatment

• Talk to a healthcare provider about STIs and ask about getting tested.
• To find STI information and testing sites near you, call CDC-INFO at 1-800-232-4636 or visit CDC’s GetTested webpage.
• You can analyze your chances of getting an STIs with the STD Wizard, a free interactive online tool based on the CDC’s STI Treatment Guidelines, available in English and Spanish.

Community Support

• The American Congress of Obstetricians and Gynecologists provides patient education resources on STIs, including genital herpes, gonorrhea, chlamydia, syphilis, hepatitis B and C in pregnancy, HIV and pregnancy, HPV, and HPV vaccines.

Note: This resource list is for informational purposes only. It is not comprehensive, and an organization’s inclusion does not constitute an endorsement by NIH. 

Research Information

The National Institutes of Health (NIH) is the largest public funder of biomedical research in the world. NIH invests most of its budget in medical research seeking to enhance life and to reduce illness and disability. NIH-funded research has led to breakthroughs and new treatments helping people live longer, healthier lives, and building the research foundation that drives discovery.

NIH conducts research on STIs to understand the microbes that cause the infections, identify factors that affect the chances of getting or spreading STIs, understand how STIs affect pregnancy and long-term health, develop diagnostic tests, and develop new interventions to treat STIs, prevent people from acquiring STIs, and prevent their spread in different populations. NIH research and training activities helped to establish and define the field of contraceptive microbicides, products that both prevent pregnancy and reduce the transmission of STIs, including HIV. Researchers are also trying to understand the best ways to communicate with people about STIs and effective preventive measures. Some of this research includes studying attitudes, perception, and knowledge of STIs and their prevention; understanding the use and misuse of contraception to prevent STIs; and understanding the misinformation surrounding the topic while aiming to identify the best settings for providing education about sexual health.

NIH also supports research focused on ways to prevent HIV mother-to-child transmission and new infections. This includes:

• The Maternal-Fetal Medicine Units (MFMU) Network conducts clinical trials and observational studies aimed at reducing adverse pregnancy-related issues, including how STls might affect pregnancy outcomes. MFMU Network studies have included an observational study of hepatitis C infection in pregnancy; a trial to prevent congenital cytomegalovirus transmission; and trials evaluating antimicrobial treatments for bacterial vaginosis and trichomoniasis to prevent preterm birth.
• The International Maternal Pediatric Adolescent AIDS Clinical Trials (IMPAACT) Network conducts research to prevent mother-to-child transmission of HIV. IMPAACT's trials helped identify antiretroviral medicine strategies that are safe for mothers with HIV and most effective at preventing transmission to their babies during pregnancy and breastfeeding, shaping U.S. and global guidelines. The network currently focuses on evaluating new ways to protect HIV-exposed newborns during and after breastfeeding.
• The HIV Prevention Trials Network (HPTN) develops and evaluates HIV prevention strategies for populations at risk. HPTN research provided critical information to guide the use of long-acting injectables during pregnancy and breastfeeding to prevent mother-to-child transmission of HIV. Researchers currently study biomedical, behavioral, and structural HIV prevention strategies; how other STIs increase HIV risk; and how to combine broader STI screening, treatment, and prevention with HIV prevention.

Find NIH-funded research projects using NIH RePORTER, a searchable database of current and past research projects supported by NIH and other federal agencies.