STD stands for   sexually transmitted disease, also called sexually transmitted infections (STIs). STDs are infections that spread from person to person through sexual activity, including anal, vaginal, or oral sex. STDs are caused by bacteria, parasites, and viruses.

Many health care providers use the term “infection” instead of “disease”, because a person with an infection may have no symptoms but still require treatment. When untreated, an STI can become a disease.

HIV is a sexually transmitted infection, but it can progress to a disease called   acquired immunodeficiency syndrome (AIDS)  when HIV infection is untreated with HIV medicines. Other examples of STDs are   chlamydia,   gonorrhea,   human papillomavirus (HPV) infection, and   syphilis.

Behaviors that put people at risk for HIV also increase their risk for other STDs. These behaviors include the following:

• Having sex without a   condom.
• Having sex with many partners, especially anonymous partners.
• Having sex while using drugs or alcohol. Using drugs and alcohol can affect a person's judgment, which can lead to risky behaviors.

Having an STD can make it easier to get HIV. For example, an STD can cause a sore or a break in the skin, which can make it easier for HIV to enter the body. Having HIV and another STD may increase the risk of HIV   transmission.

Sexual abstinence (never having vaginal, anal, or oral sex) is the only way to eliminate any chance of getting an STD. But if you are sexually active, you can take the following steps to lower your risk for STDs, including HIV.

Choose less risky sexual behaviors.

• Reduce the number of people you have sex with.
• Do not drink alcohol or use drugs before and during sex.

Use condoms correctly every time you have sex.

• Visit this website from the Centers for Disease Control and Prevention (CDC) to learn   how to use condoms correctly.

Take HIV medicines daily. Treatment with HIV medicines (called   antiretroviral therapy or ART) helps people with HIV live longer, healthier lives. One of the goals of ART is to reduce a person's   viral load  to an undetectable level. An   undetectable viral load  means that the level of HIV in the blood is too low to be detected by a   viral load test. People with HIV who maintain an undetectable viral load have effectively no risk of transmitting HIV to their HIV-negative partner through sex.

If your viral load is not undetectable—or does not stay undetectable—you can still protect your partner from HIV by using condoms and choosing less risky sexual behaviors. Your partner can take medicine to prevent getting HIV, which is called   pre-exposure prophylaxis (PrEP). PrEP is an HIV prevention option for people who do not have HIV but who are at risk of getting HIV. PrEP involves taking a specific HIV medicine every day to reduce the risk of getting HIV through sex or injection drug use.

To learn more, read the HIVinfo   Pre-Exposure Prophylaxis (PrEP)  fact sheet.

Symptoms of STDs may be different depending on the STD, and not everyone will experience the same STD symptoms. Examples of possible STD symptoms include painful urination (peeing), unusual discharge from the vagina or penis, and fever.

STDs may not always cause symptoms. Even if a person has no symptoms from an STD, it is still possible to pass the STD on to other people.

Talk to your health care provider about getting tested for STDs and ask your sex partner to do the same.

To find STD information and testing sites near you, call CDC-INFO at 1-800-232-4636 or visit CDC's   GetTested   webpage.

STDs caused by bacteria or parasites can be cured with medicine. There is no cure for STDs caused by viruses, but treatment can relieve or eliminate symptoms and help keep the STD under control. Treatment also reduces the risk of passing on the STD to a partner. For example, although there is no cure for HIV, HIV medicines can prevent HIV from advancing to AIDS and reduce the risk of HIV transmission.

Untreated STDs may lead to serious complications. For example, untreated gonorrhea in women can cause   pelvic inflammatory disease, which may lead to infertility. Without treatment, HIV can gradually destroy the   immune system  and advance to AIDS.

From CDC:

• Diseases & Related Conditions
• HIV and Substance Use in the United States
• HIV Prevention
• Protecting Others

From the Eunice Kennedy Shriver National Institute of Child Health and Human Development:

• Sexually Transmitted Diseases (STDs)
• About Sexually Transmitted Diseases (STDs)

Resources:

HIV Source