Sexually transmitted infections (STIs)
How STIs spread, why many have no symptoms, and which can be cured.
✓ Clinically reviewed · Catherine, RN & Juah, RN
📝 Audio transcript
Sexually transmitted infections (STIs).
More than 30 kinds of bacteria, viruses and parasites can be passed on through vaginal, anal or oral sex. Some STIs can also pass from a mother to her baby during pregnancy, childbirth or breastfeeding.
STIs often cause no symptoms. More than 1 million curable STIs are caught every day around the world, and most of them have no symptoms.
Four common STIs can be cured with medicine: syphilis, gonorrhoea, chlamydia and trichomoniasis. Infections caused by viruses, such as herpes and HIV, cannot be cured, but medicines can control them.
Untreated STIs can cause serious problems, including infertility in women, problems in pregnancy, stillbirth and harm to newborn babies. They can also increase the risk of getting HIV. Pregnant women are among the groups for whom STI testing is especially important.
When should I get help?
- If you are worried you may have an STI — many have no symptoms, so ask for a test.
- If you are pregnant, ask about STI testing at your antenatal check-up.
- If a partner tells you they have an STI.
Key things to remember
- Many STIs have no symptoms.
- Syphilis, gonorrhoea, chlamydia and trichomoniasis can be cured.
- Partners need treatment too, to stop reinfection.
📖 Read the full lesson
More than 30 kinds of bacteria, viruses and parasites can be passed on through vaginal, anal or oral sex. Some STIs can also pass from a mother to her baby during pregnancy, childbirth or breastfeeding.
STIs often cause no symptoms. More than 1 million curable STIs are caught every day around the world, and most of them have no symptoms.
Four common STIs can be cured with medicine: syphilis, gonorrhoea, chlamydia and trichomoniasis. Infections caused by viruses, such as herpes and HIV, cannot be cured, but medicines can control them.
Untreated STIs can cause serious problems, including infertility in women, problems in pregnancy, stillbirth and harm to newborn babies. They can also increase the risk of getting HIV. Pregnant women are among the groups for whom STI testing is especially important.
📚 Sources
- World Health Organization — Sexually transmitted infections (fact sheet) 10 Sep 2025 · accessed 31 Oct 2026
Written in plain language from these sources. It does not imply endorsement by these organizations.
HH-ART-009 · Version 1.0 · Last updated 4 Nov 2026
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