An STI — sexually transmitted infection — is an infection that spreads from one person to another through close physical contact during sex. That is the whole definition. Some are caused by bacteria, some by viruses, a couple by tiny parasites or mites. In Ireland, most of them are treatable, and many are completely silent — you can have one without ever knowing.
If you take one thing from this page
STIs are common, mostly treatable, and rarely the catastrophe people fear when they first look this up. The dangerous bit is not having one — it's not knowing you have one. Testing solves that, and in Ireland testing is free.
STI vs STD — which is right?
You will see both terms. "STD" — sexually transmitted disease — is the older one. "STI" — sexually transmitted infection — is what clinicians, the HSE, and most public-health bodies now use. The reason for the shift is honest: most STIs do not cause obvious "disease". Many have zero symptoms. Calling them all "diseases" was scary and a bit misleading. "Infection" is more accurate.
So when you see "STD" in older content, or "STI" in newer content, they mean the same set of conditions. We use STI throughout this site because that's what the HSE uses.
How do you catch one?
The short version: through close physical contact during sex. The slightly longer version:
- Vaginal sex — penis in vagina. Can transmit almost every STI.
- Anal sex — penis in anus. Same risk profile as vaginal sex; for HIV specifically, receptive anal sex carries the highest single-act risk.
- Oral sex — mouth on genitals. Lower risk than penetrative sex but absolutely not zero. Chlamydia, gonorrhoea, syphilis and herpes can all transmit this way.
- Skin-to-skin contact in the genital area — for HPV, herpes, pubic lice and scabies. Condoms reduce but don't eliminate this risk because they don't cover every skin surface.
- Sharing needles — for HIV and hepatitis. Not strictly "sex" but it gets grouped with STIs in clinic discussions.
One thing worth saying because it comes up so often: you almost certainly did not catch your STI from a toilet seat, a swimming pool, or a borrowed towel. The viruses and bacteria involved don't survive long outside the body. The person you caught it from is overwhelmingly likely to be a recent sexual partner — and overwhelmingly likely to have had no idea they had it.
The most common STIs in Ireland
The HSE's HPSC (Health Protection Surveillance Centre) tracks STI notifications across the country. Year on year, the patterns are roughly the same. Here are the ones you are most likely to encounter, in rough order of how common they are:
Chlamydia
The most common bacterial STI in Ireland by a wide margin. Mostly silent. Easily cured with a short course of antibiotics. Full guide →
HPV (human papillomavirus)
Extremely common — most sexually active adults will encounter it. Most cases clear on their own. Vaccination is free for many in Ireland. Full guide →
Genital herpes (HSV-1 or HSV-2)
Very common. Often mild or symptomless. No cure but easily managed with antiviral tablets when needed. Full guide →
Gonorrhoea
Rising again in Ireland after years of decline. Bacterial — treated with antibiotics, though resistance is becoming a concern. Full guide →
Syphilis
Once almost eliminated in Ireland; now back at meaningful numbers, particularly in MSM (men who have sex with men) populations. Bacterial — treatable at every stage. Full guide →
HIV
Roughly 500 new diagnoses a year in Ireland. With modern treatment, HIV is a long-term manageable condition — people on treatment live normal lifespans and cannot pass HIV on. Full guide →
Genital warts
Caused by certain strains of HPV. Visible, treatable, and not the same strains that cause cervical cancer. Full guide →
Trichomoniasis, mycoplasma, bacterial vaginosis
Less famous but routinely tested for. All bacterial, all treatable with antibiotics. Often grouped under "the things they check that you've never heard of". All guides →
Pubic lice and scabies
Annoying, harmless, treatable with over-the-counter or prescription creams. Not dangerous — just unwelcome. Pubic lice · Scabies
Why does testing matter?
Three reasons, in plain language:
- Most STIs don't tell you they're there. If you wait for symptoms before testing, you will miss a lot of them — and you'll potentially pass them on to other people in the meantime.
- Caught early, almost all of them are nothing. Untreated, some can cause real problems — chlamydia and gonorrhoea can affect fertility, syphilis can damage the heart and brain decades later, untreated HIV is still serious. Caught early, none of that has to happen.
- Knowing your status is the kind thing for partners. Whatever a positive result means for you, knowing it means you can talk about it, use protection, or get treatment, before you pass it on to someone else.
None of this requires a moral reason. You don't have to justify it. "I just want to know" is a complete sentence.
How testing works in Ireland
The Irish system is genuinely good. Three free options exist for almost everyone:
- Free HSE sexual health clinic — every county has one. No GP referral. No charge. Find yours →
- Free home test kit from sh24.ie — anyone 17+ in Ireland. Order online, test at home, post your sample, get results by text or phone.
- Your GP — they will do a full screen. Costs €50–€70 typically, or free with a medical card or GP Visit Card.
The whole process is covered in plain language on How testing actually works — what they ask, what they take, how results come back. Worth reading if you've never been before.
What if you do have one?
Honestly: most likely it is fine. Almost every STI in Ireland is either curable with a short course of antibiotics, or manageable with a tablet you take when needed, or — for HIV specifically — a treatment that is now so good that people on it cannot pass HIV on and live normal lifespans.
The clinician will tell you what you have, what the treatment is, and whether you need to tell recent partners (the HSE has a free anonymous partner notification service if you do). It is, almost always, a much smaller event than the panic-search at 2am suggested it would be.
Next step
If you are reading this because you are wondering whether you should test: the answer is almost always yes. Free, anonymous, available in every county. Find your nearest free service →
Where to go from here
- Symptoms — or not? — how to tell what is and isn't a symptom
- How testing actually works — the whole process, step by step
- STI testing in Ireland — the hub — every county, every condition, every option
- Resources — HSE links, helplines, support services
Important: Nothing on STI.ie is medical advice. Always speak to a clinician for diagnosis or treatment. HSE Sexual Health Line: 1800 700 700 (free, anonymous).