Sexually transmitted diseases

Sexually transmitted diseases (STDs) are infections passed from an infected person to another through oral sex, anal or vaginal sexual intercourse, or genital touching. There are many types of STDs, and they are caused by bacteria, parasites or viruses.

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STD causes and risk factors


There are three major causes of STDs that are passed through sexual activity:

  • Bacteria. Includes chlamydia, gonorrhea and syphilis.
  • Viruses. Includes HIV/AIDS, herpes simplex virus, human papillomavirus, hepatitis B, hepatitis C, cytomegalovirus (CMV) and Zika.
  • Parasites. Includes Trichomonas vaginalis, and insects such as scabies mites and crab lice or pubic lice.

HIV, hepatitis B and hepatitis C can also be transmitted via blood by sharing contaminated needles or using contaminated body piercing or tattooing equipment.

Regardless of how you may be exposed and infected, you can spread an STD even if you have no symptoms.

Risk factors for catching an STD

If you are sexually active in any way, you are at risk. Other factors that may increase that risk include:

  • Abusing alcohol and/or drugs. Can lead to risky behavior and choices.
  • Being forced to have sexual activity. See your provider as soon as possible for tests, treatment and emotional support.
  • Being young. Half of all STDs in the U.S. occur in people between the ages of 15 and 24.
  • Having multiple sexual partners. Applies to having partners at the same time as well as monogamous, consecutive relationships.
  • A history of STDs.
  • Injecting drugs. This behavior spreads many serious infections, including HIV, hepatitis B and hepatitis C.
  • Unprotected sex, including oral sex. Improper or inconsistent use of condoms can also increase your risk. Oral sex infections are less common, but they can still be transmitted unless you use a latex condom or a dental dam.

Avoiding these factors will help reduce your risk of catching an STD.

Common signs and symptoms of STDs

(and when to see your primary care provider)

Depending on the type of STD, symptoms may appear just a few days after exposure, they may appear for the first time after many years, or you may never have symptoms. You should see your primary care provider promptly if you have:

  • Discharge from your penis or vagina.
  • Lower abdominal pain.
  • Painful or burning urination.
  • Pain during sex.
  • Rash on your torso, hands or feet.
  • Sores or bumps on your genitals, in your mouth or in your rectum.
  • Sore, swollen lymph nodes, particularly in your groin.
  • Unusual or odd-smelling vaginal discharge, or vaginal bleeding.

Common types of sexually transmitted diseases

Most STDs affect both men and women, but women tend to experience more serious health problems, including problems for the babies of pregnant women. The most common types of STD are:

  • Chlamydia. A bacterial infection of the genital tract.
  • Genital herpes. Caused by a type of the herpes simplex virus (HSV) that enters your body through small breaks in your skin or mucous membranes and is highly contagious. Most people with HSV never know they have it because they have no signs or symptoms or the signs and symptoms are so mild they go unnoticed.
  • Gonorrhea. A bacterial infection of the genital tract, which can also grow in your mouth, throat, eyes and anus.
  • HIV. An infection with the human immunodeficiency virus. HIV interferes with your immune system, and it can lead to AIDS, a chronic, life-threatening disease.
  • Hepatitis A, hepatitis B and hepatitis C. Contagious viral infections that also affect the liver.
  • Human papillomavirus (HPV). According to the Centers for Disease Control and Prevention (CDC), HPV is the most common STD in the U.S. There are several forms of HPV. Some forms put women at high risk of cervical cancer, other forms cause genital warts, and other forms never result in symptoms.
  • Syphilis. A bacterial infection that typically affects the genitals, skin and mucous membranes, and can also involve the brain, heart and other body parts.
  • Trichomoniasis. A common STD caused by a microscopic, one-celled parasite called Trichomonas vaginalis.

Treating an STD

Your primary care provider will develop the best treatment plan for the type of STD you have and any symptoms. There are many types of STDs, so there are many types of treatments.

STDs caused by bacteria are usually treated easily and effectively, but viral STDs are more challenging and can’t always be cured. Your treatment plan may include:

  • Antibiotics. Can cure many bacterial and parasitic STD infections, including gonorrhea, syphilis, chlamydia and trichomoniasis.
  • Antiviral drugs. Typically prescribed for herpes, HPV, hepatitis and HIV.
  • Vaccines. Can help prevent the spread of some STDs and prevent you from catching an STD again, especially in the case of some forms of HPV.

Your plan will also include treatments to help get rid of sores, rashes, pain and any other symptoms.


Center for Disease Control and Prevention (CDC). Sexually Transmitted Diseases (

National Institute of Allergy and Infectious Diseases (NIAID). Sexually Transmitted Diseases (