What Are STDs?

Sexually transmitted diseases (STDs) include viral, bacterial and parasitic infections that are passed from person to person during physical intimacy.

Is This an Emergency?

If you are experiencing serious medical symptoms, seek emergency treatment immediately.

Rather than STDs, the current preference in medical literature is to use the term sexually transmitted infections (STIs), emphasizing the fact that many infections remain silent and may not cause obvious disease. For example, the human papillomavirus (HPV) is thought to infect the vast majority of sexually active people at some point in their lifetimes, yet most of these infections resolve without causing genital warts or cervical cancer, which are the “disease” states of HPV.


STIs are extremely common, with an estimated 20 million new cases in the United States every year. More than half of these new infections occur in young people between the ages of 15 and 24. More than 1 million Americans are living with HIV infections, another million people are infected with chlamydia, in excess of 7 million people are infected with trichomonas each year and another million people are dealing with new cases of genital warts.

Contrary to popular belief, STIs are not restricted to the genitals. Virtually every STI can be passed to the mouth (and vice versa) during oral sex, and the same is true for anal sex. Additionally, some STIs can be transmitted to the eyes and skin.

Bacterial STIs

Gonorrhea is often associated with chlamydia, and together these two bacterial STIs are the major culprits for developing chronic pelvic pain and infertility if they are not diagnosed and treated early on after initial infection.

Syphilis is another bacterial STI that can be cured with old-fashioned penicillin. Historically, syphilis is called “the great imitator” because, if left untreated, it can affect virtually every system in the body.

Bacterial STIs can be cured with antibiotics, although there is increasing bacterial resistance to these drugs.

Viral STIs

The most common STI is the human papillomavirus (HPV), which causes both genital warts and cervical, penile, anal and oral cancers. More than 79 million people are currently infected with HPV in the United States, and each year we have approximately 14 million new cases of genital warts. We have no cure for HPV, but now we are fortunate to have excellent prevention for HPV through vaccines.

Perhaps the best-known viral STI is HIV, the virus that causes AIDS. We currently have more than 1 million people living in America with HIV infection. Although we do not yet have successful vaccine prevention or antiviral cures, people infected with HIV are now living longer, productive lives through aggressive multidrug medical therapy.

Herpes simplex virus (HSV) is yet another extremely common viral STI. The Centers for Disease Control and Prevention (CDC) estimates that 80 percent of adults living in the United States are infected with HSV type 1 (the primary cause of cold sores, but also the cause of the majority of genital herpes cases as well). Additionally, one in six Americans over the age of 12 is estimated to be infected with herpes simplex virus type 2 (HSV-2). Our antiviral medications have greatly reduced the severity and frequency of recurrent disease as well as significantly diminished transmission to noninfected partners.

Parasitic STIs

Although more people have heard of syphilis than trichomoniasis, “trich” infects an estimated 5 million Americans each year (versus 56,000 cases of syphilis). Trich remains a challenge to diagnose, but is relatively easily treated with antibiotics. The most challenging issue with untreated trich infections is that they greatly increase an individual’s risk of contracting viral STIs like herpes and HIV (because the trich irritates the lining of the vagina, breaking down natural barriers and defenses against other STIs). Vaginal trich infections also cause premature childbirth and low birth weights (if they occur during pregnancy).

“Crabs” are tiny parasitic insects that are actually considered the single most infectious STI because rates of transmission after a single episode of intercourse exceed 90 percent. Scabies are similar parasites that dig into the skin. These STIs can also be transmitted without intercourse, as they can cling to bed linens, towels or underwear. Note that they can not, however, be transmitted from a toilet seat. STIs can be surprisingly silent, so please be aware that the only way you can be sure which STI you have or do not have is to be tested.