Sexually transmitted diseases (STDs) are caused by sexually transmitted infections (STIs). They are spread mainly by sexual contact. STIs are caused by bacteria, viruses or parasites. A sexually transmitted infection may pass from person to person in blood, semen, or vaginal and other bodily fluids.

Sometimes sexually transmitted infections are spread in ways other than sexual contact. For example, STIs can spread to infants during pregnancy or childbirth. STIs also can spread through blood transfusions or shared needles.

STIs don't always cause symptoms. A person can get sexually transmitted infections from another person who seems healthy and may not even know they have an infection.

STDs can have a range of symptoms, including no symptoms. That's why sexually transmitted infections may go unnoticed until a person has complications or a partner is diagnosed.

STI symptoms might include:

• Sores or bumps on the genitals or in the oral or rectal area.
• Painful or burning urination.
• Discharge from the penis.
• Unusual or odorous vaginal discharge.
• Unusual vaginal bleeding.
• Pain during sex.
• Sore, swollen lymph nodes, particularly in the groin but sometimes more widespread.
• Lower abdominal pain.
• Fever.
• Rash over the trunk, hands or feet.

Sexually transmitted infection symptoms may appear a few days after exposure. But it may take years before you have any noticeable problems, depending on what's causing the STI.

When to see a doctor

See a health care professional immediately if:

• You are sexually active and may have been exposed to a sexually transmitted infection.
• You have symptoms of a sexually transmitted infection.

Make an appointment with a health care professional:

• When you're considering becoming sexually active or by age 21, whichever comes first.
• Before you start having sex with a new partner.

Sexually transmitted infections can be caused by:

• Bacteria. Gonorrhea, syphilis and chlamydia are examples of STDs that are caused by bacteria.
• Parasites. Trichomoniasis is an STD caused by a parasite.
• Viruses. STDs caused by viruses include human papillomavirus (HPV), the herpes simplex virus, and the human immunodeficiency virus (HIV), which causes AIDS.

Anyone who is sexually active risks getting or spreading an STD.

Factors that may increase the risk of getting an sexually transmitted infection include:

• Having unprotected sex. Vaginal or anal sex with an infected partner who isn't wearing a condom (latex or polyurethane) greatly increases the risk of getting an STD. Condoms made from natural membranes aren't recommended because they're not effective at preventing some STIs. Not using condoms properly or not using them each time also can increase risk.

  Oral sex may be less risky. But sexually transmitted infections can still spread if a person doesn't use a condom (latex or polyurethane) or a dental dam. That is a thin, square piece of rubber made with latex or silicone.

• Having sexual contact with many partners. The more people you have sexual activity with, the greater your risk.
• Having a history of STIs. Having one sexually transmitted infection makes it much easier for another STI to take hold.
• Being forced to engage in sexual activity. See a health care professional as soon as possible to get screening, treatment and emotional support.
• Misuse of alcohol or use of recreational drugs. Substance misuse can inhibit your judgment, making you more willing to take part in risky behaviors.
• Injecting drugs. Sharing a needle while injecting drugs can spread many serious infections. Examples are human immunodeficiency virus (HIV), hepatitis B and hepatitis C.
• Being young. People age 15 to 24 report high levels of STIs compared to those who are older.

Spread from mothers to infants

During pregnancy or delivery, some sexually transmitted infections can be passed from mother to infant. Examples are gonorrhea, chlamydia, HIV and syphilis. STIs in infants can cause serious problems or even death. All pregnant women should be screened for STI infections and treated as needed.

Many people in the early stages of an STD have no symptoms. That's why screening is important to prevent complications.

Possible complications of sexually transmitted infections include:

• Pelvic pain.
• Pregnancy complications.
• Eye inflammation.
• Arthritis.
• Pelvic inflammatory disease.
• Infertility.
• Heart disease.
• Certain cancers, such as HPV-associated cervical and rectal cancers.

There are many ways to avoid or lower your risk of getting an STD.

• Avoid sex or sexual activity. The most effective way to avoid STDs is to not have sex.
• Stay with one uninfected partner. Staying in a long-term relationship in which both people have sex only with each other and neither partner is infected can be one way to avoid an STD.
• Wait and test. Avoid vaginal and anal sex or sexual activity with new partners until you have both been tested for sexually transmitted infections. Oral sex may be less risky. But STIs can still spread if a person doesn't use a condom (latex or polyurethane) or a dental dam. These barriers prevent skin-to-skin contact between the oral and genital mucous membranes.
• Get vaccinated. Getting vaccinated before having sex can prevent certain types of sexually transmitted infections. Vaccines are available to prevent STDs caused by human papillomavirus (HPV), hepatitis A and hepatitis B.

• Use condoms and dental dams consistently and correctly. Use a new latex or polyurethane condom or dental dam for each sex act, whether oral, vaginal or anal. Never use an oil-based lubricant, such as petroleum jelly, with a latex condom or dental dam. Also, these types of barriers give less protection for STDs involving exposed genital sores, such as HPV or herpes.

  Nonbarrier forms of contraception, such as birth control pills or intrauterine devices (IUDs), don't protect against STIs.

• Don't drink alcohol excessively or use illegal drugs. If you're under the influence of these substances, you're more likely to take sexual risks.
• Talk to your partner. Before any sexual contact, talk to your partner about practicing safer sex. Be sure you clearly agree on what activities will and won't be OK.
• Think about male circumcision. For men, evidence has found that circumcision can help lower the risk of getting HIV from a woman with HIV by as much as 60%. Male circumcision may also help prevent spread of genital HPV and genital herpes.
• Think about using preexposure prophylaxis (PrEP). The U.S. Food and Drug Administration (FDA) has approved two combination medicines to lower the risk of HIV infection in people who are at very high risk. The medicines are emtricitabine plus tenofovir disoproxil fumarate (Truvada) and emtricitabine plus tenofovir alafenamide fumarate (Descovy). These medicines must be taken every day, exactly as prescribed.

Your health care professional will prescribe these medicines for HIV prevention only if you don't already have HIV. You'll need an HIV test before you start taking PrEP and then every three months as long as you're taking it.

Your health care professional also will test your kidney function before prescribing Truvada. They will then test your kidney function every six months. If you have hepatitis B, see an infectious disease specialist or liver specialist before starting therapy.

According to the CDC, if you use Truvada daily, you can lower your risk of getting HIV from sex by about 99%. And you can lower your risk of getting HIV from injection drug use by more than 74%.

Research suggests that Descovy is also effective in lowering the risk of getting HIV from sex. But Descovy hasn't been studied in people who have receptive vaginal sex. Using added prevention, such as condoms, can lower your risk even more and prevent other STIs.

Diagnosis of an STD starts with your sexual history and current symptoms. If these suggest that you have an STD, your health care professional may do a physical or pelvic exam to look for signs of infection. Some signs of infection are a rash, warts or discharge.

Tests

Lab tests can find the cause of STD symptoms. They can also find sexually transmitted infections without symptoms.

• Blood tests. Blood tests can confirm the diagnosis of HIV or later stages of syphilis.
• Urine samples. Some STDs can be confirmed with a urine sample.
• Fluid samples. If you have open genital sores, your health care professional may test fluid and samples from the sores to diagnose the type of infection.

Screening

Testing for an STD or sexually transmitted infection in someone who doesn't have symptoms is called screening. Most of the time, STI screening is not a routine part of health care.

But when a person's risk for getting an STD changes, a health care professional may suggest screening. The risk level may change when a person is in a new setting with a higher risk, such as a prison or jail. Or it can be based on factors such as if a person has a history of sexually transmitted infections.

Experts recommend STI screening for:

• Almost everyone at least once. Guidelines suggest screening with a blood or saliva test for human immunodeficiency virus (HIV), the virus that causes AIDS, for everyone ages 15 to 65. Experts recommend that people at high risk have an HIV test every year.

  National guidelines recommend hepatitis B screening for people age 18 and older at least once, and with a test that includes a few different markers of the virus.

  Guidelines also recommend hepatitis C screening for all adults.

• Pregnant women. All pregnant women will generally be screened for HIV, hepatitis B, chlamydia and syphilis early in the pregnancy.

  Guidelines recommend gonorrhea and hepatitis C screening tests at least once during pregnancy for women at high risk of these infections.

  They also suggest hepatitis B screening at each pregnancy for everyone.

• Women age 21 and older. The Pap test screens for changes in the cells of the cervix, such as swelling an irritation, also called inflammation, precancerous changes and cancer. Cervical cancer is often caused by certain HPV strains.

  Experts recommend that women have a Pap test every three years starting at age 21. After age 30, experts recommend women have an HPV test and a Pap test every five years. Or, women over 30 can have a Pap test alone every three years or an HPV test alone every three years.

• Women under age 25 who are sexually active. Experts recommend that all sexually active women under age 25 be tested for chlamydia infection. The chlamydia test uses a sample of urine or vaginal fluid you can collect yourself.

• Reinfection by an untreated or undertreated partner is common. If you've been treated for a chlamydia infection, you should be retested in about three months. Get retested if you have a new partner.

  Experts also recommend screening for gonorrhea in sexually active women under age 25.

• Men who have sex with men. Compared with other groups, men who have sex with men run a higher risk of getting sexually transmitted infections.

  Many public health groups recommend annual or more-frequent STI screening for these men. Regular tests for HIV, syphilis, chlamydia and gonorrhea are particularly important. Evaluation for hepatitis B also may be recommended.

• People with HIV. Having HIV raises your risk of getting other sexually transmitted diseases. Experts recommend testing for syphilis, gonorrhea, chlamydia and herpes right away after being diagnosed with HIV. They also recommend that people with HIV be screened for hepatitis C.

  Women with HIV may develop aggressive cervical cancer. So experts recommend they have a Pap test at the time of the HIV diagnosis or within a year of becoming sexually active if they are under 21. Then, experts recommend repeating the Pap test every year for three years.

  After three negative tests, women with HIV can get a Pap test every three years.

• People who have a new partner. Before having vaginal or anal sex with new partners, be sure you've both been tested for STDs. However, experts don't recommend routine testing for genital herpes unless you have symptoms.

  It's also possible to be infected with an sexually transmitted infection yet still test negative, which is most common if you've recently been infected.

STDs may be treated in different ways based on the causes. Sexually transmitted infections caused by bacteria are generally easier to treat. STI infections caused by viruses can be managed and treated but not always cured.

If you are pregnant and have an STD, getting treatment right away can prevent or lower the risk of your baby becoming infected.

Treatment for sexually transmitted infections usually consists of one of the following, depending on the infection:

• Antibiotics. Antibiotics, often in a single dose, can cure many STIs caused by bacteria or parasites, such as gonorrhea, syphilis, chlamydia and trichomoniasis.

  Once you start antibiotic treatment, you need to finish the prescription. If you don't think you'll be able to take medicine as prescribed, tell your health care professional. A shorter, simpler course of treatment may be available.

  Also, it's important to avoid sexual activity until seven days after you've completed antibiotic treatment and any sores have healed.

  Experts also suggest people diagnosed with chlamydia be retested three months after treatment because there's a high chance of reinfection.

• Antiviral drugs. If you have herpes or HIV, your doctor may prescribe medicine that keeps a viral infection from getting worse, called an antiviral medicine.

  You'll generally have fewer herpes recurrences if you take what's called daily suppressive therapy with a prescription antiviral medicine. But it's still possible to give your partner herpes.

  Antiviral medicines can keep HIV infection in check for many years. But you will still carry the virus and can still spread it, though the risk is lower.

  The sooner you start HIV treatment, the more effective it is. If you take your medicines as directed, it's possible to lower the viral load in the blood so that it can't be found. At that point, you won't spread the virus to sex partners.

If you've had a sexually transmitted infection, ask your health care professional how long after treatment you need to be retested. Getting retested will ensure that the treatment worked and that you haven't been reinfected.

Partner notification and preventive treatment

If tests show that you have an STD, you need to tell your sex partners. Tell your current partners and any other partners you've had over the last three months to one year that you have an sexually transmitted infection. They will need to get tested. If they're infected, they can then be treated.

Each state has different requirements. But most states require that certain STDs be reported to the local or state health department.

Public health departments often staff trained disease intervention specialists. These specialists can help privately tell partners and refer people for treatment.

Official, confidential partner notification can help limit the spread of sexually transmitted infections. This is very important for syphilis and HIV.

It also steers those at risk for STDs to get counseling and treatment. And since you can get some STIs more than once, telling your partners lowers your risk of getting reinfected.

It can be traumatic to find out that you have an STD. You might be angry if you feel you've been betrayed. Or you might feel ashamed if you might have infected others.

And you may be worried — an STI can cause chronic illness and death, even with the best care that's available.

These suggestions may help you cope with having a STD or an STI:

• Hold off placing blame. Don't assume that your partner has been unfaithful to you. One (or both) of you may have been infected by a past partner.
• Be honest with health care workers. Their job is not to judge you, but to provide treatment and stop STIs from spreading. Anything you tell them stays confidential.
• Contact your health department. Local health departments have STD programs that give confidential testing, treatment and partner services. They may not have the staff and funds to offer every service, though.

The doctor's office is one place where you have to provide details of your sexual experience so that you can get the right care.

If you feel nervous about this topic, think about writing your experiences down. You can share this with your health care professional before or at your appointment.

What you can do

• Be aware of any pre-appointment restrictions. At the time you make the appointment, ask if there's anything you need to do in advance.
• Write down any symptoms you're experiencing, including any that may seem unrelated to the reason for which you scheduled the appointment.
• Make a list of all medications, vitamins or supplements you're taking.
• Write down questions to ask your doctor.

Some basic questions to ask your doctor include:

• What's the medical name of the infection or infections I have?
• How is the infection transmitted?
• Will it keep me from having children?
• If I get pregnant, could I give it to my baby?
• Is it possible to catch this again?
• Could I have caught this from someone I had sex with only once?
• Could I give this to someone by having sex with that person just once?
• How long have I had it?
• I have other health conditions. How can I best manage them together?
• Should I avoid being sexually active while I'm being treated?
• Does my partner have to go to a doctor to be treated?

What to expect from your doctor

Giving your doctor a complete report of your symptoms and sexual history will help your doctor determine how to best care for you.

Here are some of the things your doctor may ask:

• What symptoms made you decide to come in? How long have you had these symptoms?
• Are you sexually active with men, women or both?
• Do you currently have one sex partner or more than one?
• How long have you been with your current partner or partners?
• Have you ever injected yourself with drugs?
• Have you ever had sex with someone who has injected drugs?
• What do you do to protect yourself from STIs?
• What do you do to prevent pregnancy?
• Has a doctor or nurse ever told you that you have chlamydia, herpes, gonorrhea, syphilis or HIV?
• Have you ever been treated for a genital discharge, genital sores, painful urination or an infection of your sex organs?
• How many sex partners have you had in the past year? In the past two months?
• When was your most recent sexual encounter?

What you can do in the meantime

If you think you might have a sexually transmitted infection, it's best to avoid any sexual activity until you've talked with your doctor.

If you do take part in sexual activity before seeing your doctor, be sure to follow safe sex practices, such as using a condom.