STI - meaning and definition
AlsoSTDSTIsSTDssexually transmitted infectionSTDsexually transmitted diseasevenereal diseasesexually transmitted infectionsVDsexual infections
Not yet reviewed by a clinician. This health entry was written from the public-health sources listed below and is general information only. It is not medical advice.
Definition
A sexually transmitted infection is an infection passed from one person to another mainly through sexual contact, including vaginal, anal and oral sex and sometimes close skin-to-skin contact.
At a glance
- STIs can be caused by bacteria, viruses or parasites.
- Many STIs cause no symptoms, so testing is the only reliable way to know your status.
- Bacterial and parasitic STIs can usually be cured, while viral STIs can be treated and managed.
- Vaccines exist for some STIs, including HPV and hepatitis B.
- Some STIs can also pass through blood or from a pregnant person to a baby.
In detail
STIs are caused by bacteria, viruses or parasites. Common examples include chlamydia, gonorrhoea, syphilis, trichomoniasis, herpes, HPV and HIV. Some can also pass from a pregnant person to a baby, or through blood.
Many STIs cause no symptoms at all, which is why testing is the only reliable way to know your status. Bacterial and parasitic STIs can usually be cured with medicine, while viral STIs can be treated and managed, and some can be prevented by vaccination.
Health services increasingly prefer "STI" to "STD" because an infection is not always a disease: a person can carry an infection without being unwell. Both terms are still widely used and understood.
In a sentence
- The clinic leaflet explained which STIs can be cured and which can be managed long term.
- We both got an STI check before we stopped using condoms.
Where the word comes from
The older term "venereal disease" comes from Venus, the Roman goddess of love. It gave way to "sexually transmitted disease" in the later 20th century, and "sexually transmitted infection" became widely used from the 1990s onwards.
Not to be confused with
- Urinary tract infection
A UTI can be linked to sexual activity but is usually caused by gut bacteria and is not classed as an STI.
Common questions
What is the difference between an STI and an STD?
They describe the same group of conditions. "STI" stresses that a person can carry an infection without being unwell, so many health services now prefer it. "STD" (sexually transmitted disease) is older and still widely understood, especially in the US.
Can you have an STI without knowing?
Yes. Many STIs, including chlamydia, gonorrhoea, herpes, HPV and HIV, often cause no symptoms for long periods. Regular testing, especially after a new partner, is the reliable way to find out. A sexual health clinic or doctor can advise on your own situation.