Can STIs Really Cause Infertility? What the Data Says for Women and Men

You've probably heard that STIs can cause infertility.

Here's the short answer: in women, STIs like chlamydia and gonorrhea can trigger pelvic inflammatory disease (PID), and the resulting damage to the fallopian tubes can lead to infertility. In this article, we'll walk through what WHO, the CDC, and large-scale studies actually show — how much the risk increases, what's known about effects in men, and where mycoplasma, trichomonas, HPV, syphilis, and HIV fit in.

For context, WHO estimates that roughly 1 in 6 people worldwide experience infertility at some point in their life (WHO: Infertility). Infertility is defined as failing to conceive after 12 months or more of regular, unprotected intercourse. On the STI side, WHO estimates that more than 1 million curable STIs are acquired every day among people aged 15–49, and most of these infections show no symptoms (WHO: Sexually transmitted infections).

It's also worth noting that tubal damage — one cause of female infertility — doesn't only come from STIs. WHO also lists untreated STIs alongside complications from unsafe abortion, postpartum infections, and abdominal or pelvic surgery as contributing causes (WHO: Infertility).

One of the main pathways from an STI to infertility is through pelvic inflammatory disease (PID).

PID is an infection and inflammation of the female reproductive organs, including the uterus and fallopian tubes. It's often caused by STIs like chlamydia and gonorrhea, though non-STI infections can cause it too (CDC: About PID).

According to a review by Tsevat and colleagues, bacteria travel along the mucosal surface — from the cervix, up through the uterine lining, and into the fallopian tubes. This ascending spread shows up clinically as PID, causing inflammation of the fallopian tubes and scarring and adhesions in the pelvis (Tsevat et al. 2017). The CDC lists the complications of PID as scarring inside and outside the fallopian tubes that can block them, ectopic pregnancy, infertility, and long-term pelvic or abdominal pain (CDC: About PID).

Gonorrhea can damage the ciliated cells lining the fallopian tubes, impairing the tubes' ability to transport an egg (Tsevat et al. 2017).

Tubal-factor infertility is one of the more common causes of female infertility overall. The same review estimates that tubal-factor infertility accounts for about 30% of female infertility cases in the US and about 33% worldwide.

In Japan, too, the Japan Association of Obstetricians and Gynecologists identifies PID from chlamydia and gonorrhea as an important cause of tubal-factor infertility (Japan Association of Obstetricians and Gynecologists).

Yes — the damage can happen quietly, with no symptoms at all.

Chlamydia infection is frequently asymptomatic, and PID has no single diagnostic test — its symptoms can be mild or entirely absent (CDC: About PID, Tsevat et al. 2017).

In fact, the majority of women with tubal-factor infertility have never been diagnosed with PID. It is thought that mild or "silent" inflammation of the fallopian tubes — caused by an upper genital tract infection the person never knew they had — can still cause tubal damage or pelvic adhesions (Tsevat et al. 2017; Japanese Society for STI Research: Genital Chlamydia Infection (2008 Guidelines)). The key point is that having no symptoms does not necessarily mean there is no risk.

In recent years, this question has been studied using large-scale medical record data from Denmark, the UK, and Australia, each tracking hundreds of thousands of people (Davies et al. 2016; den Heijer et al. 2019; Reekie et al. 2019).

The risk for women who tested positive for chlamydia

Compared with women who tested negative, women who tested positive for chlamydia had a higher risk of infertility, as shown below.

All three studies rely on hospital or clinic diagnostic records, so undiagnosed cases aren't captured.

The relative risk is higher — but the absolute difference is small

In the Danish study, over an average follow-up of about 8 years, the proportion of women who sought hospital care for tubal-factor infertility was 0.6% among chlamydia-positive women versus 0.5% among women who tested negative — a difference of just 0.1 percentage points. For PID it was 3.1% vs. 2.5%, and for ectopic pregnancy, 2.2% vs. 2.0%. The authors noted that among women who were diagnosed and likely received treatment, the absolute risk was low.

That said, the elevated risk among chlamydia-positive women persisted for many years after diagnosis. The authors suggested that a positive test result might also be a marker for other risk factors, such as sexual behavior patterns or repeated undiagnosed infections (Davies et al. 2016).

What about gonorrhea?

In the Australian study, women who tested positive for gonorrhea (including cases with concurrent chlamydia) had a similar magnitude of tubal-factor infertility risk as chlamydia alone (1.38 times, 95% CI 0.67–2.86). However, the number of cases was small, and the result was not statistically significant (Reekie et al. 2019).

What happens with repeated infections?

Repeat infections raise the risk of PID further. In the Danish study, a second diagnosis carried about a 20% higher PID risk than a first diagnosis. The UK study also found that PID risk rose with the number of positive tests. However, neither study found a clear trend of increasing tubal-factor infertility risk with repeat infections (Davies et al. 2016; den Heijer et al. 2019).

What happens if an infection goes untreated or progresses to PID?

The CDC states that, left untreated, about 10–15% of women with chlamydia will develop PID (CDC: Infertility & STDs (archived)). However, a review by Haggerty and colleagues notes that in studies following asymptomatic populations over time, the rate of progression to PID appears lower than that. At the time of that review, no prospective study had directly tracked how often untreated infection leads to infertility (Haggerty et al. 2010).

Estimates of infertility risk after PID vary somewhat by source:

• CDC: about 1 in 8 women who have had PID will have difficulty getting pregnant (CDC: About PID) — this figure traces back to a 1999 source.
• Tsevat et al.: about 15% develop tubal-factor infertility, with risk rising after repeat episodes of PID (Tsevat et al. 2017).
• Haggerty et al.: up to 18% may become infertile after an episode of symptomatic PID, regardless of cause (Haggerty et al. 2010).

It's worth noting that all of these cohort studies looked at diagnosed infections, so treatment status alone can't be used to judge infertility risk. What matters most is catching an infection — before it's able to progress to PID or another complication — through testing and prompt treatment.

Women

In women, the link between chlamydia or gonorrhea, PID, tubal damage, and infertility or ectopic pregnancy is well established. WHO identifies gonorrhea and chlamydia as major causes of PID and infertility in women (WHO: Sexually transmitted infections).

Early detection and treatment can help reduce the risk of complications. CDC treatment guidelines note that testing and treating sexually active women for chlamydia and gonorrhea reduces PID risk (CDC: STI Treatment Guidelines (PID)). The CDC also recommends annual chlamydia and gonorrhea screening for sexually active women under 25 (CDC: About PID).

PID itself is treatable if caught early. But treatment doesn't reverse damage that's already occurred, and the risk of complications rises the longer treatment is delayed (CDC: About PID).

Men: What Is Epididymitis?

In men, infection can inflame the epididymis — a coiled tube where sperm mature and are stored — a condition called epididymitis. The CDC notes that acute epididymitis is commonly caused by STIs such as chlamydia, gonorrhea, and Mycoplasma genitalium, as well as enteric bacteria like E. coli. Symptoms typically include pain and swelling in the scrotum, usually on one side. Sudden, severe pain can signal testicular torsion, a surgical emergency — seek care immediately if that happens (CDC: Epididymitis).

According to a Tokyo Metropolitan Infectious Disease Surveillance Center explainer, about 5% of men with chlamydia infection develop epididymitis (fever-free swelling and pain in one side of the scrotum) as part of the disease's presentation; the data isn't broken down by treatment status (Tokyo Metropolitan Infectious Disease Information Center: Genital Chlamydia Infection).

Does Epididymitis Cause Infertility?

Not always — but it can.

According to a German review, sperm concentration that drops during an acute episode of epididymitis usually recovers within 3–6 months. Looking specifically at men who had already had acute epididymitis, pooled data suggest that approximately 1 in 10 men may have persistent azoospermia (no sperm in the semen), and about 3 in 10 may have persistent oligozoospermia (a low sperm count). It's important to note this figure describes the outcome among men who had epididymitis — not the proportion of all men who get an STI. Duct obstruction is considered a key reason semen quality doesn't fully recover, and even when antibiotics successfully clear the infection, whether infertility develops afterward is hard to predict (Schuppe et al. 2017).

The same review notes that among men seen at male-infertility specialty clinics, 5–15% have azoospermia, and about 40% of those cases are obstructive (a blockage in the sperm duct). Of those obstructive cases, 18–47% are due to infection or inflammation. Surgical reconstruction or reconnection of the sperm ducts may be an option in some cases.

The CDC lists reducing complications like infertility and chronic pain as one of the goals of treating epididymitis (CDC: Epididymitis).

Men: STIs and Male Infertility Overall

• Systematic review (70 studies): for most STIs, roughly equal numbers of studies found a link and found no link. The exceptions were ureaplasma and mycoplasma (mainly M. hominis), which were found more often in infertile men. However, ureaplasma is also common in healthy people's bodies, so this result should be interpreted with caution (Khalafalla et al. 2023).
• Chlamydia: a 2025 meta-analysis pooling 26 studies found that men with a history of chlamydia infection had roughly 3.7 times the infertility risk of men without one. Even after adjusting for publication bias (the tendency for studies with striking results to get published more often), the association held at roughly 2.8 times (Open Forum Infect Dis 13(1)).

Beyond chlamydia and gonorrhea, here's what the evidence says about each of these infections and infertility.

Mycoplasma genitalium

A 2015 meta-analysis found that women infected with this bacterium had roughly 2.1 times the risk of PID compared to uninfected women — a statistically significant difference. For infertility, the result was roughly 2.4 times, but with much wider variation between studies, so this was not statistically significant (Lis et al. 2015). Tsevat and colleagues describe the link as "suggestive but not conclusive," and note there's currently no basis for testing for this organism as part of an infertility workup (Tsevat et al. 2017).

Trichomonas

WHO lists links to low birth weight, preterm birth, and premature rupture of membranes when untreated, as well as an increased risk of PID (WHO: Trichomoniasis). Some studies do suggest a link to infertility, but many didn't adjust for other infections, so the evidence isn't considered strong enough to establish causation (Tsevat et al. 2017). Evidence for an effect on male infertility isn't strong enough to draw a conclusion either (Schuppe et al. 2017).

HPV

WHO notes that HPV causes cervical cancer, among other conditions (WHO: Sexually transmitted infections).

Women: a meta-analysis of 11 studies (15,450 women total) looked at this question. Among the six studies focusing only on high-risk HPV types — the types most likely to cause cervical cancer — infected women had about 2.3 times the risk of infertility compared with uninfected women. This difference was statistically significant. Among 7 studies that combined high- and low-risk types, the number was similar (roughly 2.1 times), but with much wider variation between studies, and this was not statistically significant. The authors concluded that high-risk HPV may be a risk factor for infertility, but likely isn't the sole cause (Yuan et al. 2020).

Men: a meta-analysis of 25 studies (6,942 men) found that those with HPV detected in their semen had lower sperm motility and poorer sperm morphology than those without HPV (Garolla et al. 2024). Another meta-analysis found roughly three times higher odds of male infertility among men with seminal HPV (Andrology 2020). That said, other reviews note that results across studies remain mixed (Khalafalla et al. 2023).

Syphilis

For syphilis, the main concern is not infertility but its effects on pregnancy. WHO notes that untreated syphilis during pregnancy can cause stillbirth, neonatal death, preterm birth, and low birth weight. If syphilis goes untreated, is treated too late, or is treated with the wrong antibiotic, adverse birth outcomes occur in 50–80% of cases. WHO recommends testing at the first prenatal visit, with immediate treatment if positive (WHO: Syphilis). As for male infertility, the systematic review mentioned earlier found no original studies examining a link (Khalafalla et al. 2023).

HIV

A 2025 scoping review covering 59 studies found that HIV-positive women may experience changes in menstruation, including lighter or absent periods, and that markers of more severe disease — low CD4 count, high viral load — were associated with lower anti-Müllerian hormone (AMH), a marker of ovarian reserve. Some studies also reported lower pregnancy rates and higher miscarriage rates. In HIV-positive men, abnormal semen parameters have also been reported, particularly among those with more advanced disease. On the other hand, for HIV-serodiscordant couples (HIV-positive male partner) undergoing IUI or IVF, pregnancy outcomes were comparable to those of HIV-negative couples. The authors caution that the underlying studies varied widely in disease stage and treatment status, which limits how broadly these findings can be applied (Chada et al. 2025).

WHO also notes that couples with differing HIV status may still need fertility care (WHO: Infertility).