Finding out you’ve tested positive for a sexually transmitted infection (STI) can feel worrying. And if your partner gets tested and their results come back negative, you might be left thinking: how is that possible?

You’re not alone, this is a really common question. The good news is that there are many reasons why your test results might be different, and it doesn’t always mean what you might first think.

How can one partner test positive, and the other negative?

There are a few key reasons why this can happen:

1. Timing of the test
   Some STIs don’t show up straight away. There’s something called a window period, the time between being exposed to an infection and it showing up on a test. If your partner was tested very soon after exposure, their result might come back negative even if they’ve been infected. They may need to test again later.
2. Different infections, different timelines
   Each STI has its own “detection window.” For example:
   • Chlamydia and gonorrhoea can usually be picked up within 2 weeks.
   • HIV and syphilis may take several weeks before they show up on a test.
     This means it’s possible for one person’s infection to show, and the other’s not yet.
3. Not everyone catches everything
   Just because you’ve had unprotected sex doesn’t always mean both partners will get the same infection. Transmission depends on lots of factors, including the type of sex you had, whether protection was used, and even individual biology.
4. Past vs. present infections
   It’s possible that one partner had an STI before the current relationship, and only found out after testing now. This can sometimes cause confusion or worry about trust, but often it simply means the infection has been there unnoticed for some time.

It’s not about blame

One of the hardest parts of getting an STI result is the emotions that come with it. It’s natural to feel shocked, upset, or even worried about what it means for your relationship.

But remember: STIs are common, and having one doesn’t mean anyone has done something “wrong.” Many infections have no symptoms and can be carried unknowingly for months or even years. Testing positive is about your health, not your worth, and it doesn’t mean your partner has been unfaithful.

What should you do next?

If you and your partner have different results, here’s what to do:

• Follow your treatment plan
  If you’ve been prescribed medication, take it as directed. Most STIs, like chlamydia and gonorrhoea, can be treated quickly with antibiotics.
• Encourage your partner to re-test
  If they tested negative but it was very soon after sex, they may need to repeat the test after the right window period. This helps confirm their result.
• Use protection
  Until treatment is complete (and a follow-up test confirms it’s cleared, if advised), use condoms to avoid passing the infection back and forth.
• Keep the conversation open
  It might feel awkward, but talking honestly with your partner helps you both stay healthy and avoid misunderstandings.

Protecting yourselves going forward

Once treatment is done, the best way to avoid future confusion is regular testing and protection.

• Condoms: The only method that protects against both STIs and pregnancy. If you’re under 25, you can get free condoms through the eC-Card app.
• Regular testing: Even if you feel fine, testing is important. You can order a free, discreet STI self-testing kit through our online portal.
• Talk openly: Checking in with your partner about sexual health can help build trust and reduce anxiety.

We’re here to support you

Testing positive for an STI can feel overwhelming, but you’re not alone. Suffolk Sexual Health Service offers free, confidential testing, treatment, and advice. Whether you’re confused about your results, worried about talking to your partner, or just want reassurance, we’re here to help.

Final word

If you’ve tested positive but your partner hasn’t, don’t panic, there are many reasons why results can differ. What matters most is that you both look after your health, follow treatment, and test again if needed.

STIs are more common than you might think, and managing them is simply part of taking care of yourself. With the right treatment, protection, and support, you and your partner can move forward with confidence.