Medically reviewed by Patrick Carroll, MD
Written by Our Editorial Team
Last updated 11/05/2019
In 1495, the French army invaded Naples, enjoyed a little drunken debauchery and introduced a devastating disease to much of Europe. The “great pox” started with sores on the genitals, followed by a fever and muscle pain. And then weeks or months later, painful ulcers would appear all over the body.
Within a few years, this disease — which would later be known as syphilis — had spread to Switzerland, Germany, England, Scotland and the Holy Roman Empire. Within 20 years, it was a worldwide phenomenon.
This brief history lesson is to say that sexually transmitted infections (STIs) — which have also been called venereal disease (VD) or sexually transmitted diseases (STDs) — are not a new problem.
They’ve been around for hundreds of years. Literally. And they probably aren’t going anywhere any time soon.
There are a number of common STIs that you’ve probably heard of (like chlamydia, gonorrhea and herpes) and some others that may be less familiar (like trichomoniasis or Mgen). These infections are caused by bacteria, parasites, viruses or other pathogens (germs) that are passed between partners during sexual behavior.
We’ve put together a list of the most common STIs so that you can know what's out there and the signs and symptoms you should be looking for if you’re at risk for STIs (as in, if you’re having unprotected sex, have more than one partner or have a partner who has other partners). The goal here is to remind us all that while STIs are common, testing is easy, treatment is possible and prevention is vital.
Chlamydia is the most common bacterial STI in the United States. The Centers for Disease Control and Prevention (CDC) estimates that there are 2.86 million cases of chlamydia each year. It’s called the silent infection because many men and women who have it never exhibit any symptoms.
Women who have symptoms tend to notice abnormal vaginal discharge and pain or burning when they urinate. Men may also notice abnormal discharge from their penis or burning when they pee. Though it’s less common, men may also experience unilateral testicular pain.
Chlamydia can be spread to the rectum and cause anal pain, discharge or bleeding as well.
Gonorrhea is another very common STI with around 800,000 cases each year. Gonorrhea often has no symptoms In women, the mild symptoms it may have — like a burning sensation when urinating, increased discharge or bleeding between periods — are often mistaken for a UTI or vaginal infection.
Men who have symptoms may also feel a burning sensation when urinating or have discharge (that may be white, yellow or green) from their penis. Men may also have swollen or painful testicles.
Trichomoniasis, nicknamed trich because who has time for that many syllables, is actually the most common curable STI, even though it gets less attention than chlamydia and gonorrhea.
It is estimated that 3.7 million people have this infection. Trich is caused by a parasite that gets passed between partners during sex and most commonly infects the urethra in men and the vulva, vagina, cervix or urethra in women.
Only 30 percent of people who have trich notice any symptoms at all.
Men may see a discharge from the penis, feel itching or irritation inside the penis or have pain or burning after urination and ejaculation. Women may experience itching, burning, redness or soreness in their vulva or feel discomfort when they pee. They may also have unusual vaginal discharge that has a fishy smell.
Sex may also feel uncomfortable if you have trich.
The syphilis infection that struck the French Army may have been more virulent than the version we see now, but the symptoms are similar.
In the primary stage of syphilis, a person will have a sore that is typically firm, round and painless around the site of the original infection (which means these usually occur on, in or near the genitals, anus or mouth).
Even without treatment the sore will go away, but the infection is still in the body and in the secondary stage may cause a rash, swollen lymph nodes and fever. These symptoms may be very mild or even unnoticed.
Syphilis eventually goes into its latent stage where it shows no signs or symptoms but remains in the body. This stage can last for years. If untreated, the person will develop tertiary syphilis, which can wreak havoc on the heart, brain, eyes and other organs. Just ask Al Capone.
In the early 1990s, the United States came close to eradicating syphilis altogether, but it staged a comeback — in 2018, over 115,000 new diagnoses were reported — and that number is expected to keep on growing.
There are actually eight herpes viruses, but two — herpes simplex virus type 1 (HSV-1) and herpes simplex virus type 2 (HSV-2) are two of the most common.
HSV-1 and HSV-2 are spread when cells from infected skin come in contact with either broken skin (like a cut or a sore) or mucous membranes (such as the lips or genitals).
HSV-1 primarily causes oral herpes — sores on the lips or in the mouth. We sometimes call these cold sores or fever blisters. HSV-1 can cause genital herpes if transmitted during oral sex, but usually presents itself on the mouth or lips and can be spread a multitude of non-sexual ways.
Most cases of genital herpes are caused by HSV-2. It is estimated that one out of every six Americans age 14 to 49 in the United States has genital herpes and even more (about 50 percent) have oral herpes.
Some people who get genital herpes might have mild symptoms (think tiny sores mistaken for a pimple or bug bite) or no symptoms at all and won’t ever know they have the virus.
Others, however, will get fluid-filled blisters or clusters of blisters on the lips, genitals, rectum, inside the mouth or at the back of the throat. The blisters then break, leaving sores that are painful and may be slow to heal.
The first time you experience a genital herpes outbreak, you may also feel like you have the flu with fever, body aches and swollen glands. This first outbreak is usually the worst, but recurrences are generally less brutal, and usually occur when you’re run-down, stressed out or sick.
HPV or human papillomavirus is the most common
STI with an estimated 79 million infections - most in late teens and young adults - in the U.S.. There are actually over 200 strains of HPV that have been identified and more than 30 that are known to infect the genitals.
Many HPV infections are thought to carry little health risk, and the body is often able to rid itself of the virus. But certain types of the virus are known to cause genital warts, which usually appear as a small bump or groups of bumps. They can be raised, flat or shaped like a cauliflower.
Other types of the virus cause cancers of the penis, vulva, cervix, anus or throat.
HIV, or Human Immunodeficiency Virus, is a virus that attacks the body’s immune system. Specifically, it destroys CD4 cells (also known as T cells) which help the body fight off infection.
If enough of these cells are destroyed, the person becomes susceptible to infections and cancers.
AIDS — Acquired Immune Deficiency Syndrome — is a diagnosis given to HIV-positive individuals if their CD4 count drops below a certain number or they develop certain opportunistic infections.
Before the development of medications known as antiretroviral therapies (ART), people with HIV would inevitably develop AIDS and most often die within a few years. Today, however, HIV can be managed. If people with HIV take ART as prescribed, their viral load (the amount of HIV in their blood) can become undetectable.
If it stays undetectable, not only can they live long healthy lives, but their risk of spreading the virus drops dramatically.
For those who are particularly at-risk of contracting HIV, other medications like PrEP are proven to be up to 99 percent effective in preventing HIV transmission through sex. Our guide to preventing HIV with PrEP goes into more detail about how this medication works, how people can access it and what to expect from PrEP.
Mycoplasma genitalium, or Mgen, isn’t as well-known as some of the other STIs out there (possibly because we didn’t discover it until the 1980s), but it may be as widespread.
We don’t know how many people get this infection each year because there isn’t a standardized test and it’s not reportable to the CDC, but one study of almost 3,000 people who were tested for other STIs found that more of them had mycoplasma genitalium than had gonorrhea, but not as many as had trich or chlamydia.
Like the others, Mgen is often asymptomatic, but women may have pain with urination, vaginal discharge or experience discomfort during sex. Men may experience burning, painful urination or a discharge from the penis.
The only way to know for sure that you have (or don’t have) any of these STIs is to get tested. Many of these infections — including chlamydia, gonorrhea, trich and Mgen — can be detected with a simple urine test, which means you just have to pee in a cup.
Your healthcare provider may also take swabs of your urethra, or for women, of the vagina, urethra or cervix (the bottom part of the uterus). If you have had oral or anal sex, your doctor may also need to collect swabs of the rectum or throat.
Syphilis is diagnosed using a blood test. HIV testing can be done using a blood or saliva sample and results may be available as quickly as 20 minutes. There is also a blood test for herpes, but that virus is best diagnosed during an outbreak when a healthcare provider can see the sores and take swabs directly from them.
As for HPV, a healthcare provider can usually diagnose warts by looking at them, and for women, pap smears and HPV tests (done with swabs of the cervix) can detect abnormal cells before they become cancer. There is no test yet, however, for HPV of the mouth or throat.
Many tests can be done at home using testing kits that you order online and send back to a lab. If you don’t feel like swabbing your own genitals or pricking your finger, you can see your primary care provider, a urologist or head to your local clinic.
The CDC recommends that everyone (regardless of sexual history) between the ages of 13 and 64 be tested for HIV at least once in their lives. If you’re sexually active, engage in unsafe sex or share drug injection equipment, you should be tested for HIV once per year. The agency also recommends that sexually active gay and bisexual men get tested at least once a year for syphilis, chlamydia and gonorrhea.
Back in the day of Charles VIII, the only treatment for syphilis was mercury, which we now know drove people mad. And, legend has it that gonorrhea earned its nickname “the clap” because doctors would treat men by putting their penises inside large books and clapping them together to force all of the infection out.
Thankfully, medical science has come quite a ways since the good old days of slamming our penises in books. We now have ways to treat — though not necessarily cure — STIs without poisoning you with mercury.
Chlamydia, gonorrhea, trich, Mgen and syphilis can all be cured with antibiotics. To rid yourself of these infections, you’ll need to get the right prescription from a healthcare provider, take all of the medication as prescribed and wait until you’ve completed treatment before having sex again.
Also, make sure that all of your partners (and their partners) get tested and treated so you don’t end up passing infections back and forth.
It’s worth noting though that certain bacteria — especially the one that causes gonorrhea — are clever, constantly evolving and quickly becoming resistant to the antibiotics we have. It is possible that we will see cases of untreatable gonorrhea in the not-so-distant future.
The infections caused by viruses — herpes, HPV and HIV — may not be curable, but there treatments that can help minimize symptoms and long-term health consequences.
Antiviral drugs such as Valtrex® (valacivlovir) and Zovirax® (aciclovir) can help suppress the herpes virus, making outbreaks less likely and less severe. These can be taken daily or when you feel an outbreak coming on.
Antiretroviral Therapy (ART), when taken daily, can suppress HIV to the point where the virus becomes undetectable in your blood. Not only does this mean you can remain healthy, it greatly reduces the risk of passing the virus on to your partner/s.
The body is often able to clear HPV infections on its own, sometimes without a person ever knowing they have the virus. For women, pap tests and HPV tests can detect precancerous changes to the cervix, and there are procedures that healthcare providers can do that can treat the cervix and prevent abnormal cells from becoming cancer.
If you do experience HPV-induced warts, there are several popular methods of treatment and removal, including prescription topical creams, cryosurgery, electrosurgery, laser treatments and physical surgical procedures.
When an STI is left untreated, it can lead to a variety of long-term health problems.
Bacterial infections like chlamydia, gonorrhea and Mgen can spread to the internal female reproductive organs and become Pelvic Inflammatory Disease, which can in turn cause scar tissue to build up in the uterus or fallopian tubes and lead to infertility. Though less common, untreated gonorrhea can also cause infertility in men.
If allowed to go to the tertiary stage, syphilis can cause numerous health issues including blindness and death. Certain strains of HPV can lead to cervical cancer which, despite advances in detection and treatment, still kills over 4,000 women in the U.S. each year. And, unchecked HIV can still lead to AIDS and death.
It’s also important to know that having any sexually transmitted infection can make you more susceptible to contracting others, particularly HIV.
Anyone who is sexually active outside of a mutually monogamous relationship in which both partners have been tested should consider themselves at risk for STIs and practice safer sex.
Outside of avoiding sex altogether, latex condoms are the best way to prevent all of the STIs on this list.
They are highly effective at preventing those STIs transmitted through semen and other bodily fluids (which includes chlamydia, gonorrhea, Mgen and HIV). They can also help prevent STIs transmitted through skin-to-skin contact (syphilis, herpes and HPV) as long as the infected skin or sores occur in the area covered by the condom.
It is possible, of course, to have warts or sores outside the covered area, such as on the scrotum.
People who are at high risk of HIV may also consider taking PrEP, or Pre-exposure Prophylaxis. People on PrEP take antiretroviral drugs called either Truvada® or Descovy® daily, which can reduce the risk of contracting the virus by 99 percent. PrEP does not work nearly as well if not taken consistently, however.
We also now have a vaccine that protects against nine types of HPV, including the types most likely to cause cervical and genital cancers. The CDC recommends that all young people — regardless of biological sex or gender — get the vaccine at age as young as nine. The FDA has approved the vaccine for use by individuals through age 45, so if you missed it when you were younger, check with your healthcare provider to see if it’s appropriate for you.
Some health experts believe that widespread vaccination could prevent 90 percent of all cervical cancer cases worldwide.
Regular testing is also considered part of prevention efforts because the only way to stop spreading these common STIs is if everyone who has one knows about it and treats it.
Medical science has come a long way since King Charles’ troops brought syphilis back from Italy, but the idea that STIs are punishment for bad behavior lingers even today. Our collective guilt over sex and the stigma and shame that surround STIs continues to get in the way of us seeking the testing and treatment we need.
Instead of wasting energy feeling bad about STIs, we need to educate ourselves, our friends and our partners, and work to prevent the spread of infections by using latex condoms, getting vaccinated, considering PrEP or antiviral drugs if at risk, seeking testing regularly and finding treatment when needed.