Recognising STIs: How to know if you have an infection
Sexually transmitted infections such as chlamydia, gonorrhoea, or syphilis are a widespread global health issue. In 2022, the number of reported STI cases in Europe increased significantly. For example, reported cases of gonorrhoea (also known as “the clap”) rose by 48% compared to the previous year (ECDC, 2024). These infections often occur without symptoms, which increases the risk of unnoticed transmission or long-term complications. In this article, you will learn how to recognise a sexually transmitted infection, which symptoms are common, and how to protect yourself effectively.
Table of contents
- What is a sexually transmitted infection (STI)?
- How do you recognise a sexually transmitted infection and what are the symptoms?
- When should I get tested?
- Asymptomatic, untreated STIs and long-term consequences
- Summary
What is a sexually transmitted infection (STI)?
A sexually transmitted infection is an infection caused by bacteria, viruses, fungi, or parasites that is mainly transmitted through unprotected sexual contact. Modes of transmission include vaginal, anal, and oral sex, as well as close skin-to-skin contact. Some STIs can also be transmitted through blood, infected needles, or during childbirth. STIs are classified based on the type of pathogen:
| Pathogen | Infection (Pathogen name) |
|---|---|
| Bacteria | Chlamydia (Chlamydia trachomatis) |
| Gonorrhoea (Neisseria gonorrhoeae) | |
| Syphilis (Treponema pallidum) | |
| Viruses | HPV (Human papillomavirus) |
| Herpes simplex (Herpes simplex virus) | |
| HIV (Human immunodeficiency virus) | |
| Hepatitis B (Hepatitis B virus) | |
| Parasites | Trichomoniasis (Trichomonas vaginalis) |
Source: WHO, 2024
How do you recognise a sexually transmitted infection and what are the symptoms?
In many cases, people do not realise they are infected with an STI because many sexually transmitted infections are asymptomatic or cause only mild symptoms. However, even without symptoms, STIs can be transmitted and may lead to health complications if treatment is delayed. About 50% of men and 70% of women infected with chlamydia show no symptoms (Mayo Clinic, 2024).
If symptoms do occur, they may typically present as follows:
Some STI symptoms are not gender-specific. These often include unusual discharge from the genitals or anus, burning or pain while urinating, and itching or irritation in the genital or anal area. Sores, blisters, or warts may appear in the genital, oral, or anal area. Some infections may also cause rashes on the body, palms, or soles of the feet.
The table below shows gender-specific symptoms:
| Typical STI symptoms in men | Typical STI symptoms in women |
|---|---|
| Unusual discharge from the penis | Vaginal discharge with a different colour (e.g., green or yellow), consistency, or smell |
| Pain or swelling in the testicles | Lower abdominal pain or pain during sex |
| Pain during ejaculation or intercourse | Spotting between periods or heavier menstrual bleeding |
| Sores or blisters on the penis, anus, or mouth | Sores or blisters in the genital area or mouth |
If you experience symptoms of a sexually transmitted infection, you should seek medical help immediately, get tested, and receive appropriate treatment. Avoid unprotected sex and inform current and past sexual partners so they can also get tested (Mayo Clinic, 2023, Cleveland Clinic, 2023).
You can get tested for sexually transmitted infections at general practitioners, gynecologists, urologists, or dermatologists. Many public health clinics also offer STI testing. Alternatively, self-tests like those from Homed-IQ are available, allowing you to test yourself easily and anonymously from the comfort of your home.
When can symptoms of a sexually transmitted infection appear?
The incubation periods indicate how long it may theoretically take for the first symptoms to appear, even though many sexually transmitted infections remain asymptomatic and cause no complaints.
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Chlamydia: 1 to 3 weeks
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Gonorrhoea (the clap): 2 to 7 days
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Syphilis: 10 to 90 days
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Genital herpes: 2 to 12 days
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Trichomoniasis: 4 to 28 days
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HPV: weeks to months (often asymptomatic)
Knowing the incubation periods helps identify asymptomatic courses more easily and enables early action to prevent complications and further transmission of the infection (Cleveland Clinic, 2024).
When should I get tested?
Testing for a sexually transmitted infection is recommended in specific situations to detect infections early and prevent their spread. Here are the most important reasons to get tested:
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After unprotected sex: The risk of infection increases significantly without protection such as condoms or dental dams.
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When symptoms occur: Symptoms like unusual discharge, painful urination, or skin changes in the genital area should be examined by a medical professional as soon as possible.
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After a new partner: Testing before starting a new sexual relationship helps protect both partners.
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If your partner is infected: Testing is necessary even in the absence of symptoms, as many infections can be asymptomatic. Repeated transmission between partners can occur if only one person is treated.
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Regularly in risk groups: People with multiple sexual partners or men who have sex with men should get tested regularly. Testing every 3–6 months is recommended.
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During pregnancy: STI testing is part of preventive care to minimise the risk of transmitting the infection to the baby.
Source: CDC, 2024
Asymptomatic, untreated STIs and long-term consequences
Asymptomatic sexually transmitted infections pose a significant health risk because they can go undetected, remain untreated, and continue to be passed on. They also increase the risk of serious long-term complications:
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Infertility: Especially in women, untreated chlamydia and gonorrhoea can lead to pelvic inflammatory disease (PID), which damages the fallopian tubes and may result in infertility.
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Chronic pain: Ongoing inflammation in the genital or pelvic area is a common consequence of untreated STIs.
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Increased HIV risk: Some STIs, such as herpes or syphilis, cause inflammation and skin lesions that raise the likelihood of HIV transmission.
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Cancer: Certain high-risk HPV types can lead to cervical cancer or other types of cancer such as anal cancer over time.
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Pregnancy complications: Untreated infections during pregnancy may result in miscarriage, premature birth, or infections in the newborn.
Sources: Cleveland Clinic, 2021; YaleMedicine, 2024
Summary
Sexually transmitted infections such as chlamydia, gonorrhoea, or syphilis often show no symptoms, making diagnosis and prevention more difficult. Typical symptoms—such as unusual discharge, burning during urination, or skin changes—appear with varying incubation periods depending on the infection. Early STI testing, especially after unprotected sex or in the presence of symptoms, is crucial to detect infections and avoid long-term consequences such as infertility or increased HIV risk.
