What You Need to Know About the Most Common STIs

Sexually transmitted infections (STIs) are mainly spread from person to person through the exchange of certain body fluids during sexual contact.

Key takeaways:
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    Sexually transmitted infections (STIs) are most commonly spread from person to person through sexual activity. Vaginal, anal, or oral sex can pass an STI to another person.
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    There are dozens of STIs caused by bacteria, viruses, and other microorganisms. These include chlamydia, gonorrhea, syphilis, herpes, genital HPV, HIV, and trichomoniasis.
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    In addition to genital fluids, some STIs can spread through genital skin-to-skin contact and blood. Others can spread from mother to baby during birth or breastfeeding.
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    Many STIs don’t cause any symptoms. If there are symptoms, they commonly include unusual discharge from the vagina or penis, painful urination, itching, or lesions.
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    All STIs can either be cured or treated.

There are over thirty STIs, including chlamydia, gonorrhea, syphilis, genital herpes, genital HPV, HIV, and trichomoniasis.

What is an STI?

A sexually transmitted infection (STI), also known as a sexually transmitted disease (STD), is a condition that mainly spreads from person to person through sexual contact. Any form of sexual contact can pass an STI to another person, including vaginal, anal, or oral sex.

There are over 30 STIs caused by bacteria, viruses, parasites, or other microorganisms that thrive on the warm, moist mucous membranes of the genitals, mouth, and throat. Two of the most common STIs globally – chlamydia and gonorrhea – are bacterial. Other STIs, such as genital human papillomavirus (HPV) and human immunodeficiency virus (HIV), are viral.

Anyone sexually active person can get an STI. Those infected can develop a wide range of symptoms depending on the type of infection and body part involved. Many STIs, however, don’t cause any symptoms. Because people often have no signs of disease, but can still infect others, the use of the term “STI” instead of “STD” has become more common.

What are the most common STIs?Heading

  • Chlamydia: Caused by infection with Chlamydia trachomatis, chlamydia is known as a “silent infection” because most people who get it don’t experience symptoms. If symptoms are present, they commonly include painful urination or unusual discharge from the vagina or penis. Without treatment, chlamydia can lead to pelvic inflammatory disease, infertility, chronic pelvic pain, and pregnancy complications in women.
  • Gonorrhea: Caused by infection with Neisseria gonorrhoeae, gonorrhea infects the urethra in women and men and the female reproductive tract. This bacterium can also infect the anus, mouth, throat, and eyes. Like chlamydia, symptoms often don’t appear but may include painful urination or unusual discharge from the penis or vagina.
  • Syphilis: This potentially life-threatening infection is caused by a bacterium called Treponema pallidum. The first sign of infection is a highly contagious sore (chancre) in, on, or around the genitals, lips, or mouth. The second stage involves a rash, and wart-like patches on the skin, usually with flu-like symptoms. With no treatment, syphilis can cause damage to the heart, brain, and nervous system, and it can be fatal.

Viruses that remain inactive in the body for years cause viral STIs. The most common include:

  • Genital herpes: Herpes causes painful sores on the skin and genitals and is caused by two types of herpes simplex viruses: HSV-1 (commonly causing cold sores on or near the lips) or HSV-2 (usually causing genital herpes). Although there’s no cure for herpes, medications are available that reduce the severity and length of active outbreaks.
  • Genital human papillomavirus (HPV): About 40 types of HPV can infect the genitals, mouth, and throat through sexual contact. Also known as genital HPV, these types can cause harmless growths (warts) on or near the vagina, cervix, penis, anus, or scrotum. High-risk types of genital HPV can also cause precancerous lesions and genital cancers.
  • Human immunodeficiency virus (HIV): HIV is a virus that attacks the immune system. Infection often starts with a flu-like illness, and then symptoms disappear for ten years or longer. If left untreated, HIV infection can progress to a potentially life-threatening condition called AIDS (acquired immunodeficiency syndrome). Though there’s no cure for HIV/AIDS, medications that prevent or slow the virus’s growth are available.

Other common STIs include:

  • Trichomoniasis: Caused by infection with Trichomonas vaginalis, a protozoan parasite, trichomoniasis affects more women than men. If symptoms are present, they can include unusual discharge, itchy genitals, and painful urination. Some women may also develop pain during sex. However, about 70% of people don’t have symptoms.

How do STIs spread?

STIs mainly spread through the exchange of body fluids such as semen, vaginal fluid, and blood during sexual activity. They can also spread by other types of intimate physical contact.

Some STIs like chlamydia and gonorrhea are spread primarily through genital fluids. Other STIs, like genital herpes, syphilis, and genital HPV, most often spread through genital skin-to-skin contact. STIs such as HIV can also spread through blood, including when sharing needles or other injection drug use equipment. Still others, including syphilis, gonorrhea, genital herpes, and HIV, can also be transmitted from mother to baby during childbirth and breastfeeding.

How are STIs diagnosed and treated?

Depending on the suspected infection and a person’s sexual health history, healthcare providers use blood tests, urine tests, swabs, and other office tests to diagnose STIs. The good news is that although some STIs are not curable, all are treatable. And in most instances, early diagnosis and treatment will decrease the risk of long-term health complications.

Antibiotics can cure most bacterial STIs. Viral STIs are not curable and tend to be more difficult to treat than bacterial STIs, but medications can relieve symptoms of these infections.

Sexually transmitted infections (STIs) can spread through semen, vaginal fluid, blood, and other bodily fluids during sexual contact and sometimes from mother to baby or by sharing needles. There are many types of STIs, including those that are bacterial and those that are viral. Although viral STIs are not curable, all STIs are treatable. If you have STI symptoms or think you may have been exposed, consult a healthcare provider for testing and treatment right away.


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