Can you have an STI even if you tested negative?

Reviewed by Dr Bhavini Shah

If you’re sexually active, there’s always a bit of risk associated with having sex with a new or casual partner. This is the case even if you use condoms – although it’s true that condoms do reduce your risk of STIs significantly.

Many STIs – including the most common one, chlamydia – don’t always cause symptoms in their early stages. This means that you might not know you’re infected until you get tested.

However, STI testing is complicated by the fact that different infections have different “window periods”.  This is the time between exposure and when an accurate test can detect an infection. Certain STIs will show up on a test within a couple of weeks of infection, while others will take much longer. This means if you test too early for certain STIs, the infection might not show up. 

In other words, it’s possible to have an STI even if you tested negative the first time. But how many people know this? To find out, we asked 500 Brits to tell us how long they think you need to wait to get an accurate test result for a number of different STIs. 

Interestingly, 66% of those surveyed were unaware of STI ‘testing windows’, with 62% admitting they didn’t know testing too early could lead to an inaccurate result and 12% revealing they have received a false-positive result. 

To find out more, Dr Bhavini Shah, GP from LloydsPharmacy Online Doctor explains why some STIs take longer to diagnose than others, how they are spread, and the treatments available.

How soon after unprotected sex can I test for an STI?

Different STIs have different incubation periods, and therefore different testing windows. Below you’ll find the testing window periods for some of the most common STIs in the UK.

14 days after exposure 

• Chlamydia 
• Gonorrhoea

Interestingly, our study revealed 35% of Brits are unaware that Chlamydia and Gonorrhoea tests will not show accurate results until at least 14 days after exposure. In fact, one in four believe you can get an accurate result immediately after contracting these STIs. 

Dr Bhavini Shah from LloydsPharmacy Online Doctor shares her advice when testing for Chlamydia or Gonorrhoea and getting treatment:

“To ensure you get the most accurate test results for chlamydia and gonorrhoea, it’s important to wait two weeks after possible exposure before taking a test. "

“While it is possible to be tested before then, you may be advised to repeat the test later on if you receive a negative result. Often, these STIs do not present symptoms, so you might not know your sexual partner has them unless they tell you.”

Treatment for Chlamydia and Gonorrheoa

“Because chlamydia is a bacterial infection, it can easily be treated with a 7-day course of oral antibiotics, such as Doxycycline. You need to take your antibiotics exactly as directed by your doctor and avoid having sex during your treatment."

“Gonorrhoea is also treated with antibiotics. In most cases, treatment involves having an antibiotic injection, however it’s sometimes possible to have an antibiotic tablet instead of an injection. Most symptoms - such as discharge - should clear up within a few days of the treatment. Pain in the tummy and testicles may take a couple of weeks to fully clear. If your symptoms persist, contact your local sexual health clinic or GP."

45 to 90 days after exposure 

• HIV – certain types (including Online Doctor’s HIV tests) can detect the virus sooner than others 

When it comes to HIV testing, the ‘window period’ can range between 45 to 90 days after exposure, with more advanced tests detecting the virus in 45 days. Shockingly, 32% of respondents from our study believe you can get an accurate HIV test result by testing much earlier, in the days immediately after exposure. A further 44% thought you would get an accurate result after 14 days, however, this can lead to a false positive result and means you would need to test again after the ‘window period’.

“If you think you’ve been exposed to HIV, it’s important to seek medical advice as soon as possible. Exposure usually happens through unprotected vaginal or anal sex, however it can also happen during oral sex. You might also be exposed to HIV by sharing needles or other injecting equipment."

“Within the first 72 hours of exposure, it’s possible to prevent infection by taking post-exposure prophylaxis (PEP). This is available from sexual health and GUM clinics, as well as hospital A&E departments, although it’s normally only prescribed to people who are considered high risk."

“Symptoms of HIV are the same for men and women. These can include:

• Fever and high temperature
• Severe headaches
• Sore throat
• Muscle aches
• Joint pain
• Body rash 
• Swollen glands
• Skin lesions 

“However, HIV can be symptomless. The infection goes through stages. The asymptomatic stage is where someone with HIV will experience no symptoms."

Treatment for HIV

“HIV is managed with antiretroviral medications that inhibit the virus's replication in the body. This enables the immune system to repair itself and reduce further harm.
“A combination of HIV drugs is necessary because the virus can rapidly adapt and develop resistance. Different combinations of HIV medications are effective for different people, so your treatment will be tailored specifically to you by your doctor.”

12 weeks after exposure 

• Syphilis

If you’re testing for syphilis, you’ll need to wait 12 weeks after exposure to ensure you get an accurate result. Interestingly, 87% of respondents were unaware of this, highlighting the importance of understanding the different ‘window periods.’

“It’s easy for syphilis to go undetected as it can take up to three weeks for symptoms to appear. They are often mild, tend to change over time, and may come or go."

“The symptoms of syphilis include small sores on the genitals or anus. These are typically painless, and many people only have one of them. However, it’s also common to notice white patches in the mouth, a painless rash on the palms of the hands and the soles of the feet, and white or grey warty growths on the genital areas. Flu-like symptoms, swollen glands, and patchy hair loss may also be experienced."

“If syphilis is not treated in the early stages, it can stay dormant in the body, showing no signs or symptoms. This can lead to life-threatening conditions years after you were initially infected including heart problems, seizures, personality changes, and nerve issues."

Treatment for Syphilis

“Early-stage syphilis can be treated with antibiotics, such as penicillin, administered via injection or tablets. In the later stages of syphilis, antibiotics can still treat the STI and prevent further damage but may not reverse any harm that has already been caused by the infection."

“If you test positive for syphilis, you should contact your GP or local sexual health clinic to discuss treatment options.”

Genital warts and genital herpes

Two of the more common STIs in the UK – genital warts and genital herpes – can only be diagnosed if you’re having symptoms, which 66% of people in our study were unaware of. If you develop any lumps, growths, sores or blisters around your genitals, you should go to the sexual health clinic to have a physical examination. 

“To diagnose genital warts, symptoms must be present. Your healthcare provider will look at the lumps around the genital area, sometimes using a magnifying lens. While there are currently no swab or blood tests used to detect genital warts, as they are caused by the HPV virus, a cervical screening test can detect HPV infection on the cervix, even if there are no visible symptoms."

“When testing for genital herpes, symptoms also need to be present for an accurate diagnosis. If you’re displaying physical symptoms such as small fluid-filled blisters in or around the genital area, contact your GP or healthcare provider as soon as possible for testing. In most cases, a swab of fluid will be taken from the blisters in the affected area, which will then be sent for the lab for testing. A blood test can also detect the presence of antibodies to the herpes simplex virus.”

What happens if I get a test too early?

If you get a test too early, it may not pick up the infection, which means you run the risk of getting a misleading result. To avoid this, you shouldn’t use an STI test without speaking to a doctor or nurse first, as they’ll be able to advise you on the best time to get tested.

There are some circumstances where you might be advised to take more than one test. If you think you’ve been exposed to HIV, for instance, you might be told to get a test as soon as possible, followed by another test to confirm the first result a few weeks or months later.

Should I wait to get tested if I’m having symptoms?

No, if you’re having symptoms you should go to a sexual health or GUM clinic. A doctor or nurse can give you a test, assess your symptoms and – if necessary – give you a physical examination. If they think there’s a strong chance you have an STI like chlamydia, they might prescribe treatment before you get your test results back. 

Is it safe to use home STI test kits?

Yes, it’s safe to use home STI tests, as long as they come from a trusted provider e.g. the NHS or a registered pharmacy like LloydsPharmacy Online Doctor.

At Online Doctor we use a secure form to ask you questions about your sexual history, the last time you had sex, and whether you’re having any symptoms. If clinicians don't think it would be a good idea for you to use a home test kit, they’ll let you know and advise you about what to do instead. 

Can STI test results be wrong? 

These days, STI tests are very reliable, which means you’re unlikely to get a false result provided you’ve tested for the correct STIs at the correct times.

One notable exception would be a test that doesn’t collect a sample from the correct area of the body. Although most STIs affect the genitals, some – including gonorrhoea – can affect the rectum, the throat, and even the eyes. If you take a gonorrhoea test that only involves a sample from your genitals, it may miss the infection elsewhere in your body. 

What should I do if I think I’ve been exposed to HIV?

Becoming infected with HIV is life-changing, but with early diagnosis and treatment you can live a relatively normal and healthy life. For this reason, if you think you’ve been exposed to HIV, you should seek medical advice as soon as possible.

You may even be able to avoid infection altogether if you seek emergency treatment after unprotected sex. Post-exposure prophylaxis (PEP) is a medication that can be taken in the weeks following unprotected sex to prevent infection with HIV.

Methodology

Onepulse conducted a survey on behalf of Lloyds Pharmacy Online Doctor and surveyed 500 male and female respondents in the UK between 01/11/24 and 02/11/24 in relation to STI testing windows.

References

https://www.letstalkaboutit.nhs.uk/worried-about-stis/testing-treatment-of-stis/
https://www.nhs.uk/conditions/genital-warts/
https://www.nhs.uk/conditions/genital-herpes/
https://www.nhs.uk/conditions/hiv-and-aids/diagnosis/
https://www.nhs.uk/conditions/chlamydia/treatment/
https://www.nhs.uk/conditions/gonorrhoea/diagnosis/