STIs: What Everyone Should Know
Sexually transmitted infections are one of the most common health concerns among sexually active people, and one of the most poorly understood. Despite being widespread, they remain heavily stigmatised, which means many people avoid testing, delay treatment, or carry unnecessary shame about something that is simply a health issue like any other.
What Are STIs?
Sexually transmitted infections are infections passed from one person to another through sexual contact. This can include vaginal, anal, or oral sex, as well as skin to skin genital contact in some cases. Some STIs can also be passed through blood, for example through sharing needles or, in some cases, from a pregnant person to their baby.
STIs are caused by bacteria, viruses, or parasites, and they vary considerably in how they are transmitted, how they present, and how they are treated.
How Common Are STIs?
Very. In the UK, hundreds of thousands of STI diagnoses are made every year, with chlamydia consistently the most commonly diagnosed. STIs affect people of all ages, genders, sexualities, and relationship statuses. They are not a reflection of how many partners someone has had, what kind of person they are, or how careful they have been. While there are effective ways to significantly reduce the risk of transmission, including using condoms consistently and getting tested regularly, STIs remain a reality for a significant proportion of sexually active people. Being informed is the most important thing you can do.
How STIs Are Transmitted
Understanding exactly how STIs are transmitted is important, both for reducing risk and for clearing up common misconceptions.
Most STIs are passed through the exchange of bodily fluids, including semen, vaginal fluid, anal fluid, and blood, during sexual activity. This includes vaginal, anal, and oral sex. Small cuts or tears in the skin, which are common during more vigorous sex, anal sex, fisting, or the use of larger toys or accessories, can increase the risk of transmission by providing a route for infection to enter the body.
Some infections, including herpes and HPV, are passed through skin to skin contact rather than bodily fluids, which means condoms alone do not provide complete protection against them, as they do not cover all potentially affected skin.
STIs are not transmitted through casual contact such as hugging, sharing food or drink, using the same toilet, or swimming in the same pool. You cannot get an STI from a toilet seat.
The Most Commonly Diagnosed STIs
Chlamydia
Chlamydia is a bacterial infection and the most commonly diagnosed STI in the UK. It often has no symptoms at all, which is one of the main reasons regular testing is so important.
When symptoms do occur they can differ depending on anatomy. For people with a vulva, symptoms might include unusual vaginal discharge, pain or burning when urinating, pain during sex, or lower abdominal pain. For people with a penis, symptoms might include discharge from the penis, pain or burning when urinating, or pain and swelling in the testicles.
Testing for chlamydia is simple and non-invasive. For people with a vulva, it usually involves a self-taken vaginal swab. For people with a penis, it usually involves a urine sample. In some cases, swabs from the throat or rectum may also be taken depending on sexual activity.
Chlamydia is treated with a short course of antibiotics, usually azithromycin or doxycycline. Treatment is available from a GP, sexual health clinic, or in some cases a pharmacist. It is important to complete the full course and to avoid sexual contact until both you and any partners have completed treatment. A follow-up test is recommended to confirm the infection has cleared.
Gonorrhoea
Gonorrhoea is a bacterial infection that has been increasing in prevalence in recent years in the UK. Like chlamydia, it can often have no symptoms.
For people with a vulva, symptoms might include unusual discharge, pain when urinating, or pelvic pain. For people with a penis, symptoms often include a thick yellow, white, or green discharge from the penis and pain when urinating. Gonorrhoea can also infect the throat and rectum, often with no symptoms.
Testing follows a similar approach to chlamydia: a swab or urine sample depending on anatomy, with additional swabs from the throat or rectum if relevant.
Gonorrhoea is treated with antibiotics, usually an injection of ceftriaxone. It is important to attend a follow-up test to confirm the infection has cleared, particularly given that some strains of gonorrhoea are becoming resistant to certain antibiotics. If symptoms persist after treatment, return to a sexual health clinic promptly.
Genital herpes
Herpes is caused by the herpes simplex virus and is one of the most stigmatised STIs, despite being extremely common. There are two types: HSV-1, which most commonly causes cold sores around the mouth, and HSV-2, which most commonly causes genital herpes. However, either type can affect either area, and HSV-1 can be transmitted to the genitals through oral sex.
Interestingly, 70 percent of people carry the herpes virus, the majority of whom have never had a noticeable outbreak and are entirely unaware they have it. Transmission is significantly lower when no symptoms are present, though it is not impossible, as the virus can still be shed from the skin without visible sores. Antiviral medication further reduces this risk.
When symptoms do occur, they might include tingling, itching, or soreness in the genital area, followed by small blisters or sores that can be uncomfortable. First outbreaks are often the most intense; subsequent outbreaks, if they occur at all, tend to be milder and shorter.
There is no cure for herpes, but antiviral medication such as aciclovir can reduce the frequency and severity of outbreaks and does meaningfully reduce the risk of passing the virus to a partner, though it does not eliminate that risk entirely.
It is worth being clear about how herpes is not transmitted as there are often misconceptions about this. You cannot get genital herpes from sharing a toilet, towel, swimming pool, or cutlery. It requires direct skin to skin contact with an affected area.
Syphilis
Syphilis is a bacterial infection that has seen a significant and concerning increase in diagnoses in the UK in recent years. It progresses through stages if left untreated.
In the primary stage, a painless sore called a chancre appears at the site of infection, often on the genitals, anus, or mouth. Because it is painless and sometimes hidden, it can easily go unnoticed. In the secondary stage, symptoms can include a rash, often on the palms of the hands or soles of the feet, flu-like symptoms, and patchy hair loss. If untreated, syphilis can progress to a latent stage with no symptoms, and eventually to tertiary syphilis, which can cause serious damage to the heart, brain, and other organs.
Syphilis is easily treated with antibiotics, usually penicillin, particularly in its early stages. Testing involves a blood test. Regular testing is important because symptoms can be mild or easily missed.
HIV
HIV, human immunodeficiency virus, is a virus that attacks the immune system, specifically the CD4 cells that help the body fight infection. Over time, if untreated, HIV can damage the immune system to the point where the body struggles to fight off infections and illnesses it would normally manage easily. This advanced stage is known as AIDS, acquired immunodeficiency syndrome.
HIV carries a significant amount of stigma, much of it rooted in the epidemic of the 1980s, which devastated gay and bisexual male communities in particular, as well as other populations including people from African communities. The fear, misinformation, and social attitudes of that era left a lasting mark on how HIV is perceived, and many of those perceptions no longer reflect the reality of living with HIV today.
The treatment of HIV has transformed enormously. With modern antiretroviral therapy, people living with HIV can have a normal life expectancy and an excellent quality of life. Crucially, when someone is on effective treatment and their viral load is undetectable, they cannot pass the virus on to sexual partners. This is known as U=U, undetectable equals untransmittable, and it is one of the most important developments in sexual health in recent decades.
HIV is increasingly being diagnosed in heterosexual people in the UK, and it is important that awareness and testing are not seen as relevant only to gay and bisexual men.
In terms of testing, HIV may not show up on a standard test immediately after transmission. Most tests can detect HIV reliably from around 45 days after potential exposure, though some newer tests can detect it earlier. If you think you may have been exposed to HIV very recently, within 72 hours, PEP, post-exposure prophylaxis, is an emergency medication that can prevent infection if started promptly. PrEP, pre-exposure prophylaxis, is a daily medication taken by HIV negative people to prevent transmission and is available on the NHS. We cover HIV, PEP, and PrEP in more detail in a separate article.
Genital warts
Genital warts are caused by certain strains of the human papillomavirus, HPV. They appear as small, fleshy growths on or around the genitals, anus, or surrounding skin. They can be flat or raised, single or in clusters, and are sometimes described as having a cauliflower-like appearance. They are generally painless, though some people experience itching or mild discomfort.
Genital warts are passed through skin to skin contact and can be transmitted even when no visible warts are present.
Treatment is usually carried out at a sexual health clinic and involves either freezing the warts, a process called cryotherapy, or applying a topical cream. Cryotherapy can cause some discomfort during the procedure but is generally well tolerated. Multiple treatments may be needed.
While the warts themselves can be treated, HPV can remain in the body, and warts may recur. Many people's immune systems clear the virus over time, but this process can be slower in people who smoke, as smoking affects the immune system's ability to fight off HPV. Stopping smoking can therefore support the body in clearing the virus more effectively.
The HPV vaccine, offered as part of the UK school vaccination programme, protects against the strains most commonly associated with genital warts and cervical cancer.
Trichomonas
Trichomonas, sometimes called trich, is caused by a microscopic single-celled parasite called Trichomonas vaginalis. When we describe it as parasitic, we mean that the organism lives in and feeds off the host. It is not the same as a bacterial or viral infection. It lives in the urogenital tract, affecting the vagina, urethra, and surrounding areas, and is passed through sexual contact involving the genitals, including vaginal sex and genital to genital contact.
Many people with trichomonas have no symptoms at all. When symptoms do occur, they can include itching, soreness, redness, and swelling around the genitals, an unusual discharge that may have an unpleasant smell, and discomfort when urinating or during sex.
Trichomonas is easily treated with antibiotics, usually metronidazole. Partners should be treated at the same time to prevent reinfection.
Pubic Lice and Scabies
Pubic lice, sometimes called crabs, are tiny insects that live in coarse body hair, most commonly pubic hair, but also in underarm hair, chest hair, and occasionally eyebrows or eyelashes. They are not the same as head lice. Scabies is caused by a microscopic mite that burrows into the skin. Both are passed through close physical contact, including sexual contact, and neither has anything to do with hygiene.
A common myth is that shaving pubic hair prevents or cures pubic lice. This is not true. While lice live in hair, the eggs can be attached to skin and hair follicles, and shaving alone will not eliminate them.
Symptoms of pubic lice include intense itching in the affected area, and you may be able to see the lice or their eggs attached to the hair. Scabies causes an intensely itchy rash, often in the folds of the skin, including between the fingers, on the wrists, and around the genitals.
Both are treated with topical treatments, specifically medicated creams or lotions applied to the affected areas, which are available from a pharmacy without prescription. It is important to treat all close contacts at the same time and to wash clothing and bedding at a high temperature.
Reducing Risk
Condoms, used correctly and consistently, are one of the most effective ways to reduce the risk of STI transmission during vaginal and anal sex, and provide some protection during oral sex. Dental dams offer additional protection for oral sex on a vulva or anus.
PrEP is a daily medication that is highly effective at preventing HIV transmission and is available on the NHS. PEP is an emergency medication that can prevent HIV infection if started within 72 hours of potential exposure.
Regular testing is one of the most important things sexually active people can do, allowing infections to be caught and treated early before they cause complications or are passed on to others.
Telling A Partner
If you are diagnosed with an STI, you may need to inform recent sexual partners so they can get tested. This can feel daunting, but it is an important part of sexual health responsibility and most people respond better than you might expect. Sexual health clinics can provide support with partner notification and in some cases can contact partners anonymously on your behalf.
Stigma, Shame, and Seeking Support
The stigma around STIs has deep roots. Much of it stems from the association of STIs with sexual activity itself, which has historically been treated as something shameful or morally loaded, particularly outside of marriage or monogamous relationships. The HIV epidemic of the 1980s compounded this significantly, attaching fear, prejudice, and discrimination to sexual health in ways that still linger today.
The reality is that STIs are a health matter, not a moral one. Having an STI says nothing about your character, your choices, or your worth. Stigma is the problem, not the diagnosis.
If you are concerned about your sexual health, please know that sexual health professionals are trained to be non-judgemental and are there specifically to support you. You should never feel ashamed for seeking care.
If attending a clinic in person feels difficult, there are also ways to test from home. Several services offer free postal testing kits:
SH:24 — sh24.org.uk — free online STI testing for people across the UK, offering postal testing kits. A standard kit typically involves a self-taken swab if you have a vulva, a urine sample if you have a penis, and a small blood sample obtained by a simple finger prick test providing roughly four to six millilitres of blood. Postage is included so you can return by post and results are usually text or uploaded to your account within a few days of them receiving your samples.
Sexual Health London — sexualhealthlondon.nhs.uk — a similar service to SH:24 offered to those living in London.
Many local boroughs also commission their own free postal STI testing services. Searching for your borough name alongside free STI testing will show you what is available in your area.
Results are usually returned quickly and follow-up support is available if needed.
Why Sex Actually Exists
Sex Actually exists because too many people have been left out of sex education, or taught only narrow versions of what intimacy and pleasure should look like.
Our aim is to offer inclusive, evidence-informed education that supports real experiences, real bodies, and real relationships. We are here to make conversations about sex, relationships, and wellbeing accessible, shame-free, and relevant for everyone, so you can understand yourself and others with greater confidence, curiosity, and care.
If this article sparked reflection or curiosity, you might like to explore our writing on getting tested, living with an STI, HIV, and sexual health for LGBTQIA+ people.