7 ways to prevent catching an STI

Use a condom every time, test regularly and get the vaccines you’re eligible for. No single step protects you completely, so they work best together. Here are the 7 ways at a glance:

Read more in “How to reduce your risk of catching and passing on an STI”

The NHS says using a condom every time you have sex is the best way to protect you and your partner from HIV and other STIs. Used correctly every time, condoms are also up to 98% effective at preventing pregnancy.

To get the most from them:

• use a new condom every time, for vaginal, anal and oral sex
• for oral sex, use a condom to cover the penis, or a dam, a thin square of latex or plastic, to cover the vagina
• check the packet for a CE or UKCA mark and a use by date that hasn’t passed
• use water-based or silicone-based lubricant with latex condoms, as oil-based ones can make them break
• if you share sex toys, wash them and cover them with a new condom for each person

Condoms don’t cover all the skin. Herpes, genital warts and Syphilis can still be passed on if the infected area isn’t covered. Read more in “Can you still get an STI if you wear a condom?”

It’s easier to agree on condoms and testing before you have sex than in the moment. Brook, the sexual health charity, says there’s no ideal time to talk about condoms, but generally, the earlier the better.

Questions Brook suggests asking a partner include:

• when was the last time you were tested for STIs?
• do you use condoms or any other type of protection when you have sex?
• have you had any STIs before, and did you get treatment?

You can’t tell if someone has an STI by looking. Many STIs have no symptoms, so your partner may not know either. Read more in “Should I ask my partner about getting tested for STIs?”

Many STIs cause no symptoms, so a test is the only way to know for sure. Finding an infection early means it can be treated before it causes problems or is passed on.

How often to test:

• once a year, and when you change partner: UK guidelines recommend this if you’re sexually active
• every 3 months: the same guidelines recommend this if you’re at higher risk, for example if you’ve had more than 10 partners in the last year or you take PrEP
• straight away: if you have symptoms, such as an unusual discharge, pain when you pee, or sores

A routine check without symptoms covers Chlamydia, Gonorrhoea, Syphilis and HIV.

Having one partner lowers your risk, but it doesn’t remove it. In Britain’s national sex survey, 43.3% of Chlamydia infections in men, and 60.4% in women, were in people who’d had only one partner in the past year.

UK guidelines recommend testing at the start of a relationship. Use condoms until you’ve both tested, and time the tests so they’re reliable:

• Chlamydia and Gonorrhoea: from 2 weeks after you last had sex with someone else
• HIV: a lab blood test is reliable from 45 days
• Syphilis: a test in the first 3 months can miss it, so a repeat test is recommended

Routine tests don’t check for Herpes or HPV, so a clear result doesn’t rule out every infection. Read more in “New relationship? Get tested together before you stop using condoms”

Alcohol and drugs can affect your judgement. The NHS lists losing self-control, such as having unprotected sex, among the risks of binge drinking. Someone who is very drunk or high may also not be able to consent to sex.

If you’ve had sex without a condom, some things are urgent and some are better timed:

• PEP: emergency HIV medicine has to be started within 72 hours
• emergency contraception: needs to be used within 3 to 5 days, and works better the sooner you use it
• symptoms: get tested straight away
• no symptoms: a test taken too soon can miss an infection, so test from 2 weeks for Chlamydia and Gonorrhoea

Keeping condoms with you makes it easier to use one, whatever the night brings.

Vaccines protect against some infections that are passed on through sex:

• HPV: the UK’s vaccine protects against 9 types of HPV, including those that cause most cervical cancers and genital warts. It’s offered to all children aged 12 to 13. Girls, and boys born after 1 September 2006, can catch up until their 25th birthday, and men who have sex with men can have it if they’re 45 or under
• Hepatitis A and B: recommended for men who have sex with men. Hepatitis B vaccination is also recommended for people who change partners often
• the MenB vaccine for Gonorrhoea: offered since August 2025 to men who have sex with men who are at higher risk. It gives around 30% to 40% protection
• mpox: recommended mainly for men who have sex with men who have multiple partners. Two doses give around 80% protection

A vaccine only protects against the infection it’s made for, so condoms and testing still matter.

Two medicines can prevent HIV:

• PrEP: medicine taken by people who don’t have HIV and are at higher risk of getting it. It’s taken every day, or around the time you have sex. Taken daily and correctly, it’s around 99% effective, but it doesn’t protect against other STIs
• PEP: emergency medicine taken after a possible exposure to HIV. It has to be started within 72 hours, ideally within 24, and is taken for 28 days

It also helps to know that someone with HIV who is on effective treatment, with an undetectable level of the virus in their blood, can’t pass HIV on through sex.

If you think you’ve been exposed to HIV in the last 72 hours, get urgent medical care and ask about PEP.

Better2Know offers:

• Full Screen: tests for 7 infections, including HIV, Syphilis, Hepatitis B, Chlamydia and Gonorrhoea, from 28 days after sex, with results in 3 days (5 days for the home test).
• Peace of Mind: tests for Chlamydia, Gonorrhoea and Syphilis from 14 days after sex, with results in 2 days. You can also order a home test kit.
• Chlamydia and Gonorrhoea (Urine): tests one urine sample for both infections, from 14 days after sex, or straight away if you have symptoms, with results in 2 days.

You can book any of these at one of our clinics. If you test before 45 days, a negative HIV result needs a repeat test. A Syphilis test in the first 3 months after sex can miss the infection, so you may need a repeat test. Not sure which test you need? Our Patient Care Team is available 24/7 on 020 7099 0955.

What’s the single best way to prevent STIs?

Using a condom every time you have sex. The NHS says it’s the best way to protect you and your partner from HIV and other STIs.

Can you catch an STI if you’ve only had one partner?

Yes. Your partner may have an infection from a past relationship without knowing, as many STIs have no symptoms.

How soon after sex can you test?

From 2 weeks for Chlamydia and Gonorrhoea. A lab test for HIV is reliable from 45 days, and a Syphilis test may need repeating at 3 months. If you have symptoms, test straight away.

You can’t remove every risk, but you can lower it a lot. Use a condom every time, talk to your partner, test regularly and at the start of a relationship, take care when you’ve been drinking, get the vaccines you’re eligible for, and know about PrEP and PEP.

Book a Full Screen at a clinic near you or order a home test kit. Our Patient Care Team is available 24/7 on 020 7099 0955.

Not in the UK? Choose your country from the selector at the top of the page for local tests and prices.

This article originally appeared on 4 June 2012 and was last updated on 3 October 2026.

This article is general information and not a substitute for personal medical advice.

Sources

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