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Do STIs cause male infertility?

By: Kacper Swierk, a Master’s of Biology (MBiol) candidate at Pembroke College, University of Oxford, starting his Master's project research on HIV evolution at Oxford's Zoology Department and Big Data Institute. The opinions expressed in the article are his own.

Sexually transmittable infections (STI) is a term you may almost certainly have heard to describe infections spread through unprotected sexual contact. The most common STIs include: chlamydia, gonorrhoea, HIV, HPV and syphilis. Such infections can have a deleterious effect on sperm health and male fertility. Unfortunately, both male fertility and infections with sexually transmittable diseases are stigmatised, due to the lack of awareness about them, resources and social taboo.

For many people, a diagnosis of an STI may raise questions about their potential to start or expand their family. And vice-versa, a poor result from male fertility testing may raise questions about whether someone previously experienced or is currently experiencing a sexually transmitted infection.

In this post we will cover why we should all care about STIs, why it’s a growing problem in the UK and how such an infection can impact sperm health and male fertility potential.

What is a sexually transmitted infection?

According to the World Health Organisation, a sexually transmitted infection (STI) is a bacterial, viral or parasite infection transmitted through sexual contact – oral, vaginal and anal. In principle, sexually transmitted pathogens reside in body fluids such as semen, blood, rectal fluids or vaginal fluids. The transmission occurs upon contact of the infected fluid with the recipient mucous membrane – present in partner’s penis, vulva, rectum and urinary tract. The pathogen is acquired through the mucous membrane and spread through the body to cause infection.

There are more than 30 described pathogens known to cause STIs. One of the most prevalent are bacterial – gonorrhoea, chlamydia, syphilis and viral – HIV, HPV, HSV and HBV. A majority of acquired STIs cause an asymptomatic infection. Even if symptoms occur, they are often non-specific. Therefore, in many cases an infection remains undiagnosed, while still having an impact on someone’s health.

STIs – Britain’s growing problem

Overall, the number of new cases of STIs is growing in the UK. According to the UK Health Security Agency (UKHSA), there were 392,453 new diagnoses of STIs in 2022, a 23.8% increase in comparison to 2021. It means that more than 1,050 new STI cases were reported in the UK daily.

For diseases such as gonorrhoea and syphilis record high number of diagnoses were reported – the largest annual number of new diagnoses for gonorrhoea since the records began, while the number of new syphilis cases was the highest since 1948.

Out of the most prevalent infections, only 2 showed a decreasing trend – HPV and HIV – because of the UK’s HPV vaccination programme as well as HIV prevention programmes respectively.

The most commonly diagnosed STIs in 2022 were chlamydia (199,233, 50.8% of all new STI diagnoses), gonorrhoea (82,592, 21.1%), first episode genital warts (26,079, 6.7%) and first episode genital herpes (24,910, 6.4%) (per the UKHSA).

Over the last 10 years STI diagnoses of Chlamydia, Gonorrhoea, and are increasing. COVID-19 lockdown had a marked impact and decrease in new infections.

Who’s at risk?

Initially, the risk of an STI was associated with specific groups such as men who have sex with men or sexual workers. While such groups still experience the highest burden of those infections, STIs are now present among all gender and sexual orientation groups, especially among the young demographic. 2022 marked the first year, when more new HIV cases were connected to heterosexual sexual contacts, than same-sex ones.

UKHSA named young people as a group in which the impact of STI remains the greatest. Indeed, young people (age 15-24) experience the highest diagnosis rates of most common STIs, no matter their sexual orientation. This can be worrying, as this demographic will aim to establish families in the near future and those potential infections are likely to negatively impact their fertility potential – including the male fertility potential.

STIs – a male perspective

When thinking about STIs and men, many may associate those topics with men having sex with other men. However, the bigger picture is more complex. In the UK infections such as chlamydia, genital herpes and genital warts were diagnosed more among heterosexual men than among those who engage in sex with other men. Among the young men group (aged 15-24) new STIs were reported among 27,716 heterosexual men in comparison with 11,786 cases reported among men who have sex with men in 2022. The trend is present especially for infections such as chlamydia - 10,799 infections among heterosexual men and 3,198 among men who have sex with men, genital herpes – 1,696 and 324 infections respectively and genital warts – 2,187 and 407 respectively.

Contracting a sexually transmitted infection is no longer solely a risk among small and specific groups in the margins of a picture of a society. Anyone engaging in sexual contact without protection is at risk of transmitting and getting infected with one of the STIs. With their numbers growing steadily in the UK it is now even more important to establish the impact of STIs on male fertility potential. In the next part of this post we will cover how specific STIs may affect male fertility potential, why is it important to get help, how to find support and, most importantly, how to care for reproductive health if in doubt.

STIs and male fertility

To understand why an STI may impact your fertility it is important to understand how the sperm is made, which we at Jack Fertility described here. In short, specialised structures within the testicle promote and maintain sperm production. Then the sperm matures in epididymis. Lastly, during ejaculation the sperm leaves the body through vas deferens where it is mixed with secretions from accessory organs to make semen. Infertility can be caused by damage to any of the male genital tract organs as well as damage to the sperm itself. STIs have been found to inflict damage to both, thus contributing as one of the factors behind male fertility.

What are the symptoms of most prevalent STIs? What impact can they have on reproductive health?


HBV – Hepatitis B virus – is a viral infection that can be spread through blood as well as sexual contact. It mainly affects the liver causing symptoms such as yellowing of the skin and eyes (jaundice), dark urine, nausea and pain in the abdomen. Infection can also have an impact on the sperm quality. A population study in Taiwan showed that incidence of infertility was 1.59 times higher among those infected with HBV than healthy men (Su et al., 2014). Analysis of sperm from HBV positive infertile men showed that sperm motility, morphology, volume and concentration were negatively affected (Qian et al., 2016).


HSV - herpes simplex virus – is a virus commonly known as herpes. The virus can cause two types of infections – oral and genital depending on the type of the virus acquired. Most common symptoms include blisters (cold sores) or open sores (ulcers) around the mouth or lips for the oral herpes or around genitals or anus for the genital herpes. The impact of HSV on male fertility is ambiguous. Some studies found no correlation between HSV presence and sperm quality or male fertility potential (Neofytou et al., 2009), while some associated HSV presence with abnormal semen parameters (Monavari et al., 2013). Indeed, the reasons for decreased fertility potential is often complex and cannot be correlated with one specific factor. Hence, professional support is needed to fully understand the background behind reproductive health issues.


HIV (Human Immunodeficiency Virus) can cause a chronic infection, ultimately leading to AIDS. It’s mainly spread through sexual contact and, as for now, it is not curable. During its chronic phase, it’s mostly asymptomatic – it can cause flu-like symptoms in first weeks after the infection. HIV targets human immune cells – CD4+ T cells – progressively weakening human immune system. Ultimately it leads to AIDS – a disease in which the immune system is so weak that it cannot target most of other diseases. In summary, HIV can also infect male genital tracts organs, as well as the sperm itself (Guiton and Drevet, 2023). HIV and antiretroviral therapy – a drug therapy used to decrease the viral load in the organism – can also cause sperm abnormalities – decreased sperm counts, concentration and motility (Dulioust et al., 2002; Savasi et al., 2019).


HPV - Human Papillomavirus – is the most common STI in the world. In most cases it remains asymptomatic and is eliminated from the organism. In some cases (about 10%) infection can lead to genital warts – painless growths or lumps around genitals and anus – or cancer. HPV DNA has been identified in different organs of the male genital tract as well as sperm, hence the infection is likely to impact male reproductive potential (Guiton and Drevet, 2023). Indeed, many studies showed abnormalities of sperm among HPV positive patients such as abnormal morphology and motility (Goulart et al., 2020). Additionally, infertile men are more likely to already have a HPV infection, further suggesting HPV infection as a risk factor for male infertility (Moghimi et al., 2019).


Gonorrhoea is caused by an infection with Neisseria gonorrhoeae. Infection symptoms differ between men and women; among men include: pain or burning during urination, a white, yellow or greenish discharge from penis or painful and swollen testes. WHO describes male infertility as one of the potential complications of the gonorrhoea infection. Indeed, gonorrhoea presence in infertile population is several times higher in comparison with general population (Chemaitelly et al., 2021). The reason behind it remains ambiguous and is likely a complication of immune and inflammatory response to the bacteria (Guiton and Drevet, 2023).


Syphilis is a bacterial STI caused by Treponema pallidum. Most of infections are asymptomatic. Symptomatic infections can be characterised by: a round, painless, usually hard sore (chancre) on genitals or anus – a first stage of infection. The second stage is characterised by non-itchy rash and white or grey lesions. Symptoms usually disappear, even without treatment. Untreated syphilis may severe complications, for example cardiovascular diseases. Syphilis infection can lead to testicular damage and infection – likely contributing to reduced male fertility potential. Still, no direct cases of infertility caused by syphilis have been reported (Guiton and Drevet, 2023).


Chlamydia is caused by an infection with Chlamydia trachomatis. It’s the most prevalent bacterial STI in the UK and about half of infected men are asymptomatic. Chlamydia symptoms in men can include: burning while urinating, discharge from penis and the feeling of pain or discomfort in the testicles. In rare cases untreated chlamydia may cause infertility. Chlamydia infection, like other STIs, can result in reduction in fertility potential through damage to the male genital tract or sperm (Izadi et al., 2022). Indeed, patients with chlamydia show reduced sperm quality (Guiton and Drevet, 2023). Still, there is no scientific consensus to explain the mechanism behind chlamydia related fertility reduction - reduced fertility can sometimes have more complex background.

How to get help?

The idea of contracting an STI and the potential impact it can have on your health is scary. Fortunately, there is a range of resources you can reach out to if feeling in doubt. All of them provide discreet and professional help – reaching out for help is always empowering, not a sign of weakness.

STI testing

The only way to make sure you have an STI is to get tested. Testing is suggested when you change a sexual partner or were at risk of exposure to STIs (for example because of unprotected sex).

Regular testing (for example every few months) is essential for good sexual health if you change your partners often or if you have unprotected sex. To test for STIs in the UK you can use both NHS or NHS-partnered providers as well as private providers. Both offer professional and discreet tests, often with a possibility to test-at-home, post-in tests. NHS and NHS-partnered providers work in many UK regions.

You can check your local providers here.

In most cases, after filling out a short questionnaire, you will be sent a self-test kit. The kit will arrive in a discreet and confidential package; most common test kits will contain:

- Anal, vaginal and throat swabs – used for chlamydia and gonorrhoea testing. The test is similar to self-testing for COVID-19 and requires using a small cotton bud swab in different parts of the body

- Urine sample – used for chlamydia and gonorrhoea testing. The procedure is standard for any urine test

- Blood sample – used for syphilis and HIV. The test comes with a small needle and a tube. The needle is used to prick your finger to collect drops of blood into the tube, the procedure is similar to glucose testing for people with diabetes

If you feel you would prefer more direct help, get more information before testing, or simply have some questions you can visit the website of your local sexual clinic.

You can find one based on your postcode here.

Many clinics provide both at-home and at-clinic help, including STI testing, sexual health consultations and meetings with sexual health clinicians.

An additional option for STI testing are private providers. They also offer comfortable, discreet, at-home test kits. For many you can customize which test you order - a solution helpful if you suspect a specific infection or your other local providers lack a specific test in their portfolio.

Some examples of such providers in the UK are Yoxly or Better2Know.

STI treatment

Being diagnosed with an STI is not a detrimental factor to someone’s value. Most STIs are curable, treatment is effective and, if started early, it reduces the chance of infection complications. If tested positive, the treatment options will be advised by your test provider or your local sexual health clinic. It is likely that you may need to make an appointment with your local sexual health service. Usually, the treatment requires antibiotic or anti-viral drug use. Your recent sexual partners would also need to be informed so they can get tested and care for their sexual health as well.

STI and fertility

The impact a sexually transmitted infection can have on your reproductive health is undeniable. STIs can impact both organs of your genital tract as well as sperm, causing sperm abnormalities or inflammation of reproductive organs leading to decreased fertility potential. Testing for both STIs and fertility is crucial for maintaining your reproductive potential. Both issues are intertwined – STI infection can lead to reduced fertility potential, while one of the reasons for a poor fertility test result may be a previous infection with a sexually transmitted pathogen.

At Jack Fertility we are committed to supporting all people with sperm optimise their sperm health. We provide professional, convenient and discreet from-home, mail-in fertility testing anywhere in the UK. After the sperm test results, we will support you with personalised insights into your sperm quality and future directions to improve your fertility potential or seek specialist help. Sign up to learn more and join the waitlist here:


Chemaitelly, H., et al., 2021. Global epidemiology of Neisseria gonorrhoeae in infertile populations: systematic review, meta-analysis and metaregression. Sex. Transm. Infect. 97, 157–169.

Dulioust, E., et al., 2002. Semen alterations in HIV-1 infected men. Hum. Reprod. 17, 2112–2118.

Goulart, A.C.X., et al., 2020. HIV, HPV and Chlamydia trachomatis: impacts on male fertility. JBRA Assist. Reprod. 24, 492–497.

Guiton, R., Drevet, J.R., 2023. Viruses, bacteria and parasites: infection of the male genital tract and fertility. Basic Clin. Androl. 33, 19.

Moghimi, M., et al., 2019. Significant Correlation between High-Risk HPV DNA in Semen and Impairment of Sperm Quality in Infertile Men. Int. J. Fertil. Steril. 12, 306–309.

Monavari, S.H., et al., 2013. Asymptomatic seminal infection of herpes simplex virus. J. Biomed. Res. 27, 56–61.

Neofytou, E., et al., 2009. Prevalence of human herpes virus types 1–7 in the semen of men attending an infertility clinic and correlation with semen parameters. Fertil. Steril. 91, 2487–2494.

Qian, L., et al., 2016. Effect of hepatitis B virus infection on sperm quality and oxidative stress state of the semen of infertile males. Am. J. Reprod. Immunol. 76, 183–185.

Savasi, V., et al., 2019. Effects of highly active antiretroviral therapy on semen parameters of a cohort of 770 HIV-1 infected men. PLOS ONE 14, e0212194.

Su, F.-H., et al., 2014. Hepatitis B virus infection and the risk of male infertility: a population-based analysis. Fertil. Steril. 102, 1677–1684.


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