Your Questions About Sexually Transmitted Infections, Answered

Infections passed on through sexual contact, many of which cause no symptoms.

Key takeaways

• Most common bacterial STI in the UK: chlamydia
• Symptoms: often absent, particularly in chlamydia
• Most useful single change: Test regularly if you have new or multiple partners.
• Commonest mistake: Waiting for symptoms before testing.
• See a doctor if any of the signs under "When to speak to a doctor" below apply to you.

What is Sexually Transmitted Infections?

Infections passed on through sexual contact, many of which cause no symptoms.

Why does it matter?

Most chlamydia is symptomless, which means testing rather than symptoms is what finds it before it causes harm.

Most common bacterial STI in the UK for Sexually Transmitted Infections?

Chlamydia.

Postal self-test kits for Sexually Transmitted Infections?

Available free in many areas.

Untreated chlamydia for Sexually Transmitted Infections?

Can cause pelvic inflammatory disease and infertility.

What is the single most useful thing to do?

Test regularly if you have new or multiple partners.

What is the most common mistake?

Waiting for symptoms before testing.

When should I see a doctor?

Seek urgent assessment for lower abdominal pain with fever, pain during sex, unusual discharge with pain, or testicular pain and swelling — these can indicate pelvic inflammatory disease or epididymo-orchitis, both of which can affect fertility. Seek emergency care for sudden severe testicular pain.

Where to go next

• Sexually Transmitted Infections: What to Do, in Order
• Popular Beliefs About Sexually Transmitted Infections, and What Is Actually Published
• Sexually Transmitted Infections — the reference entry
• The Evidence on Contraception Choices, Without the Hype
• What the Guidance Really Says About HIV

When to speak to a doctor

Seek urgent assessment for lower abdominal pain with fever, pain during sex, unusual discharge with pain, or testicular pain and swelling — these can indicate pelvic inflammatory disease or epididymo-orchitis, both of which can affect fertility. Seek emergency care for sudden severe testicular pain.

Where this comes from

• NHS — Sexually transmitted infections
• British Association for Sexual Health and HIV — guidance

How this page was put together

Every figure, recommendation and warning above is taken from the guidance named in Where this comes from. Nothing on this page is inferred, summarised or generalised beyond what those bodies publish: where they give a number, it is their number, and where they are silent, so are we. Pages are rebuilt whenever the underlying record changes. Sign-off by a named clinician, where it has happened, is shown at the top of the page along with the date.

Medical disclaimer

This article is general information, not medical advice. It cannot account for your own history, medication or circumstances. Always speak to a GP, pharmacist or another qualified health professional before making changes that affect your treatment, and never delay seeking medical advice because of something you have read here. In an emergency, call 999.