7 common infections that can be caused by sex

Safe sex is important for your reproductive health.

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Safe sex is important for your reproductive health.
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fizkes/ iStock

  • Safe sex is an important part of protecting your reproductive health
  • It’s important to know what infections you can catch and how to treat them
  • INSIDER consulted experts on the most common infections to look out for

Practicing safe sex is an important part of protecting your reproductive health and warding against unpleasant infections. Though most people are aware that you can contract STIs such as chlamydia and gonorrhea through sex, there are actually several more infections that can be tied to sexual activity.

INSIDER consulted with Dr. Damian Jacob Sendler, chief of the division of clinical research at Felnett Health Research Foundation, about a few of the most common infections that can be caused by sex.


Chlamydia is a very common infection, but it can have serious consequences.

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Some people don’t experience any symptoms for Chlamydia
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Chlamydia is the most commonly diagnosed STI in the United States. The Centers for Disease Control and Prevention (CDC) estimates that there about 1.7 million new cases each year.

Symptoms of chlamydia include abnormal vaginal discharge and the sensation of itching or burning. However, people don’t experience any symptoms at all. “The most concerning problem [with chlamydia] is getting pelvic inflammatory disease (PID),” Dr. Sendler told INSIDER. “Untreated PID leads to scarring of the tissues inside the uterus and Fallopian tubes, preventing women from becoming pregnant. It is the number one cause of infertility among women.”

Pregnant women can also pass chlamydia to their infants during delivery, which can lead to blindness and pneumonia in the child.


HPV is also very common and can lead to cancer.

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The majority of sexually active people are carriers of the virus
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The human papilloma virus, or HPV, is a sexually transmitted virus that can lead to cancer in all sexes.

According to the CDC, there are over 40 distinct types of HPV. HPV types 16 and 18 are responsible for about 66% of cervical cancers in the US, while HPV types 6 and 11 account for approximately 90% of genital warts. Though many people infected with HPV don’t exhibit any symptoms, the virus often leads to crusty, elevated warts on the skin of the penis, vagina, or anus.

Dr. Sendler revealed that the majority of sexually active people are actually carriers of the virus. “Nearly 80% of sexually active people have acquired HPV at some point in their life. Thanks to efficient immunological protection, most of us don’t experience any negative symptoms associated with the infection,” Dr. Sendler explained.

This is why it’s important that people with a cervix get an annual Pap smear to detect abnormal cells, which can indicate an elevated risk of developing cervical cancer in the future. “Thankfully, it takes anywhere between 10-20 years to develop full-blown cancer, so annual Pap smears are sufficient to detect abnormal changes before the patient develops cancer,” Dr. Sendler told INSIDER.

Even if you don’t have a cervix, you may want to consider getting an HPV vaccine. Dr. Sendler told INSIDER that it is an effective way of preventing a range of different cancers, including penile and anal cancer.


Gonorrhoea can cause burning discharge and infertility.

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Gonorrhea often co-occurs with chlamydia
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Gonorrhea is the second most common STI in the US. It’s also a major cause of PID, which can lead to infertility and chronic pelvic pain. The most common symptom is mucosal inflammation of the cervix or the penis, which leads to clear discharge, Dr. Sendler explained to INSIDER. Most people also report burning during sex or burning discharge coming out of the tip of the penis.

“Gonorrhea often co-occurs with chlamydia. Therefore, it is very important to receive treatment for both of these STDs. The treatment should also include your sexual partner, as they might be infected as well,” advised Dr. Sendler. “Needless to say, if one of the partners is untreated and continues to be infected, you are more likely to experience re-infection.”

The CDC reported that in 2017, 50% of reported gonorrhea cases in the US occurred in just 70 counties. Rates of infection are highest among people 15 to 29 years of age.


Syphilis is a potentially lethal infection that can go unnoticed for decades

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Syphilis can be lethal
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Syphilis is an STI that can take years to cause symptoms but is potentially fatal.

“This is a very nasty STD as it can go unnoticed, allowing the infection to progress through three stages of development that can have lethal consequences,” Dr. Sendler warned. According to the National Health Service (NHS) the early symptoms of syphilis usually show up around two or three weeks after infection. These usually include one or several painless genital ulcers.

“Not all patients who have syphilis shows up to clinic with painless genital ulcers. Some will complain about a rash that doesn’t go away, while others might come with difficulty walking,” Dr. Sendler added. As the infection progresses, an individual might notice a blotchy red rash, white patches in the mouth, or flu-like symptoms. Eventually, untreated syphilis can cause meningitis, stroke, dementia, heart problems, and a loss of the bridge of the nose.

Unfortunately, untreated syphilis in pregnant people acquired during the four years before delivery can lead to infection of the fetus in up to 80% of cases, according to the CDC. It may also result in the death of the infant in up to 40% of cases.


Trichomoniasis is caused by a parasite and can take up to a month to cause symptoms.

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Trichomoniasis can result in infertility
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Merla/Shutterstock

Trichomoniasis is caused by a microscopic parasite called Trichomonas vaginalis. It can cause thin, strong-smelling vaginal discharge, inflammation around the vagina, itchy thighs, and pain while passing urine.

Dr. Sendler advised that a physical examination of the vagina of someone with trichomoniasis might uncover inflammation of the cervix and a yellow covering on the cervix. Symptoms are more difficult to spot in men, though an examination might reveal soreness or discharge around the tip of the penis. If left untreated, this STI can result in infertility, prostate cancer, and cervical cancer.

According to the NHS, the parasite is usually spread by having unprotected sex or sharing sex toys. However, you can’t catch trichomoniasis through kissing, sharing food, oral sex, or anal sex.


Vaginitis doesn’t always occur because of sex, but having unprotected sex can make you predisposed to it.

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Vaginitis can appear during the menopause
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Vaginitis is an inflammation of the vagina that can cause redness, itching, swelling, or pain. According to Mayo Clinic, bacterial vaginosis, yeast infections, and trichomoniasis are actually all types of vaginitis.

Dr. Sendler explained to INSIDER that vaginitis can occur due to changes in the normal pH of the vaginal that disrupt the typical balance of vaginal bacteria. Symptoms can include vaginal discharge, odor, or general discomfort.

“Women who tend to have a lot of unprotected sex are at high risk of getting vaginitis due to increased loads of semen,” Dr. Sendler said. “Semen has basic pH, meaning that when a female has several ejaculations in her, the load of semen neutralizes vaginal flora and removes its natural acidity, thereby predisposing someone toward developing vaginitis.”

The Mayo Clinic also cautioned that vaginitis can also crop up after a person experiences falling estrogen levels related to menopause.


Nongonococcal urethritis is an infection that can be caused by other STIs.

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Nongonococcal urethritis is often caused by chlamydia
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Estrada Anton/Shutterstock

Nongonococcal urethritis is an inflammation of the urethra. It’s called “nongonococcal” because it’s not caused by a gonorrhoea infection. According to the American Sexual Health Association, nongonococcal urethritis is most often caused by chlamydia. The route of exposure is usually sexual, but nongonococcal urethritis can also be caused injury during the placement of a catheter or squeezing of the urethra.

Dr. Sendler informed INSIDER that the most common symptom is burning on urination or clear discharge. A small number of people might also experience reactive arthritis, which is pain in the joints of the legs caused by a reaction to the infection.

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