Every year, almost 20 million adults in the United States contract a sexually transmitted disease (STD). Some of the most common ones don’t cause symptoms. But, they can still lead to serious health problems. Learning about STDs can help protect your health now and in the future. 1. Genital Human Papillomavirus (HPV) New cases each year in the United States: More than 14 million. HPV is the most common sexually transmitted infection. There are more than 40 types of HPV. They can infect the genitals, mouth or throat. Most men and women who are sexually active will get at least one type of HPV at some point in their life. HPV spreads from one person to another through vaginal, anal or oral sex. You can get the virus even if your partner has no symptoms. Fortunately, vaccines protect people against many types of HPV. HPV infections are usually not harmful. They often go away on their own within two years. The problem is some types of HPV can lead to serious health problems. These include genital warts and cervical cancer. Most people infected with HPV have no symptoms until they develop other health issues. 2. Chlamydia New cases each year in the United States: Almost 3 million. Chlamydia is a bacterial infection. Possible signs of infection are a discharge from the penis or vagina and burning during urination. However, most people with chlamydia have no symptoms. Chlamydia spreads through sexual contact with the penis, vagina, mouth or anus of an infected person. A pregnant woman can pass chlamydia to her baby during childbirth. Even if you’ve been treated for chlamydia in the past, you can get the infection again. Your doctor can treat chlamydia with antibiotics. Without treatment, chlamydia can lead to serious health problems. It also is known to cause infertility. Women can develop pelvic inflammatory disease. Men can develop a condition that causes painful inflammation of the tube that helps carry sperm. 3. Trichomoniasis New cases each year in the United States: More than 1 million. This infection comes from a parasite that passes from one person to another during sex. It can spread from a man to a woman, a woman to a man, or from one woman to another woman. Women usually develop the infection inside the vagina or the urethra. Men can develop trichomoniasis inside the penis. The infection usually doesn’t spread to the mouth, anus or other parts of the body. Most people with trichomoniasis don’t have symptoms. Sometimes infected people experience itching or burning during urination. Discharge from the penis or the vagina is another sign of trichomoniasis. These symptoms may come and go. It takes antibiotics to get rid of the infection. 4. Gonorrhea New cases each year in the United States: More than 800,000. This STD occurs when bacteria infects the lining of a woman's reproductive tract. Gonorrhea can also develop in the urethra, mouth, throat, eyes and anus of both men and women. Gonorrhea spreads through sexual contact with the penis, vagina, mouth or anus of an infected person. A pregnant woman can pass gonorrhea to her baby during childbirth. People with gonorrhea often have mild or no symptoms. Signs of the infection include painful urination and white, yellow or green discharge from the penis or vagina. Men may develop pain in their testicles. Women can also have vaginal bleeding between periods. Treatment involves two different antibiotics. Without treatment, gonorrhea can lead to serious health problems. Women can develop pelvic inflammatory disease. This increases women’s risk of infertility and serious complications during pregnancy. Men with untreated gonorrhea can develop inflammation of the tube that helps carry sperm, which can lead to infertility. 5. Genital Herpes New cases each year in the United States: Almost 800,000. This infection comes from the herpes simplex virus (HSV), type 1 or type 2. You can get herpes by having vaginal, anal or oral sex with someone who is infected. Some people with herpes have mild symptoms. Some have none at all. Other people have outbreaks of lesions that look like blisters around their genitals, rectum or mouth. These blisters can break open and become painful sores that take a long time to heal. The fluid inside herpes sores contains the virus. You can become infected if you come in contact with it because the virus can spread through the skin. Infected people can pass the virus to their partners even if they don't have sores. Outbreaks of genital herpes can happen again and again. But the outbreaks usually become shorter and less severe over time. There is no cure for herpes. But your doctor can prescribe medicines that help prevent and shorten outbreaks and ease the pain. 6. Syphilis New cases each year in the United States: About 55,000. Syphilis is an infection caused by bacteria. Sores may develop on the genitals and lips, and in the mouth. The infection spreads through contact with these sores during vaginal, anal or oral sex. A pregnant woman can pass syphilis to her baby. It can take up to 90 days after exposure for syphilis symptoms to appear. The infection progresses in stages that can last for weeks or even years. After sores appear, a skin rash develops. This can show up on the palms of the hands and soles of the feet. In some cases, the rash can be all over the body. Left untreated, syphilis can cause serious health problems. They include brain damage, paralysis, blindness, and dementia. In extreme cases, syphilis can be fatal. Syphilis is treated with antibiotics to kill the bacteria. The more quickly you get syphilis treatment, the more completely you will recover. 7. Human Immunodeficiency Virus (HIV) New cases each year in the United States: More than 41,000. HIV is the virus that causes AIDS. When it enters the body, the virus attacks the immune system. It destroys certain white blood cells the body needs to fight off infections. Without enough of these cells, people with HIV develop other serious diseases, such as pneumonia or tuberculosis. HIV can’t survive for long outside the body. It spreads from person to person through contact with bodily fluids, such as blood and semen during vaginal and anal sex. It's possible to get HIV through oral sex, but this is not common. A pregnant woman can pass HIV to her baby during pregnancy or while breastfeeding. You can also get the virus from sharing needles or syringes with an infected person. There is no cure for HIV. But treatment with several different types of medication helps people live longer and maintain an active life. The medicine also reduces the chances of spreading the virus to others. The fact that some STDs cause symptoms and some don’t is one of the reasons why STD testing is so important. Read Getting Tested for STDs for more information on who should get tested and where you can go for the tests.