The short version
- Most STIs cause no symptoms, so 'feeling fine' proves nothing.
- Chlamydia is the most common STI in young people and is curable with antibiotics.
- Condoms are the only contraception that also reduces STI transmission.
- Oral sex can transmit STIs.
- Someone on effective HIV treatment cannot pass HIV on.
- Sexual health clinics are confidential and free in many countries, including for under-18s.
The basics without the panic
STIs (sexually transmitted infections — the same thing older resources call STDs) are infections passed on through sexual contact. Some are bacterial and curable with antibiotics. Some are viral and manageable but not curable. Getting one doesn't say anything about your character; it says you had contact with an infection, which is how all infections work.
The single most important fact: most STIs have no symptoms at all, especially early on and especially in the people carrying them without knowing. This is why 'they looked fine' and 'I feel fine' are not information. Testing is the only way to know.
Common ones, briefly
This isn't a diagnostic tool — it's orientation so the words aren't scary or mysterious. Anything you're worried about needs an actual test from a clinic or a home kit.
- Chlamydia — the most common in young people. Usually no symptoms. Curable with antibiotics. Untreated, it can affect future fertility, which is the main reason routine testing matters.
- Gonorrhoea — often symptomless too. Curable, though increasingly antibiotic-resistant, so treatment is prescribed carefully.
- HPV — extremely common, usually clears by itself, some strains cause genital warts and some can lead to cervical and other cancers. The HPV vaccine prevents the high-risk strains and is offered to teenagers in many countries. If you've been offered it and skipped it, you can usually still catch up — ask a nurse.
- Herpes (HSV) — very common, often mild or unnoticed, comes in occasional outbreaks. Not curable but very manageable with medication. Carries far more stigma than medical seriousness.
- Syphilis — rising in many countries. Starts as a painless sore that's easy to miss. Fully curable when caught, more serious if ignored.
- HIV — damages the immune system if untreated. Modern treatment works so well that someone on effective treatment has an undetectable viral load and cannot pass it on. Prevention medication (PrEP) also exists. HIV in 2020s is a manageable long-term condition, not the death sentence 1980s media taught people to imagine.
How they actually spread — and don't
Transmission happens through vaginal, anal and oral sex, and through genital skin-to-skin contact for some infections. Sharing needles transmits blood-borne ones. Some can pass from parent to baby during pregnancy or birth.
They don't spread from toilet seats, sharing cutlery, hugging, or swimming pools. Oral sex is not risk-free — that's the most common gap in what people believe.
Lowering your risk
Nothing except no contact is 100%, but the gap between 'no precautions' and 'basic precautions' is enormous.
- External or internal condoms, used from start to finish, including for oral and anal sex. They're the only contraception that also reduces STI transmission.
- Dental dams for oral sex on a vulva or anus.
- Get the HPV vaccine if it's available to you. Hepatitis B vaccination too.
- Test between partners, and roughly every 3–6 months if you have new or multiple partners.
- Don't share needles for anything — drugs, steroids, piercings, tattoos.
- Talk before, not after. "When did you last get tested?" is a normal question, not an accusation.
Testing: less of an ordeal than you think
Sexual health clinics are free and confidential in many countries, including for under-18s, and they are extremely used to seeing teenagers. Most testing is a urine sample, a self-taken swab, or a finger-prick blood test. Often no physical examination at all.
You can usually order a free postal kit online, do it at home, and get results by text. If you're under 16, staff will normally still keep it confidential unless they're worried you're being harmed or exploited — and if that's happening, having them know is a good thing.
Signs that mean go sooner rather than later: unusual discharge, pain when peeing, sores, lumps, unusual bleeding, pain during sex, or a partner telling you they've tested positive. Also just having had unprotected sex — no symptoms required.
Myths worth binning
❌You can tell if someone has an STI.
Usually you can't. Most infections are invisible and symptomless.
❌You can't get an STI from oral sex.
You can — chlamydia, gonorrhoea, herpes, syphilis and HPV all transmit orally.
❌Two condoms are safer than one.
They rub against each other and are more likely to break. Use one.
❌The pill protects against STIs.
It prevents pregnancy only. It offers zero STI protection.
Check what stuck
Quick multiple choice, with an explanation after every answer. Nobody sees your score.