How likely am I to get HIV based on the act?

UK guidelines estimate the chance of getting HIV from a single exposure to someone with HIV who isn’t on effective treatment:

• Receptive anal sex (being the bottom): 1 in 90
• Insertive anal sex (being the top): 1 in 666
• Receptive vaginal sex: 1 in 1,000
• Insertive vaginal sex: 1 in 1,219
• Giving or receiving oral sex: less than 1 in 10,000
• Sharing needles or other injecting equipment: 1 in 149
• Needlestick injury: 1 in 333
• Human bite: less than 1 in 10,000

These are estimates from studies, and other studies give slightly different figures. The risk is higher if the person with HIV has a high viral load. For sex, there’s no risk at all if they’re on effective treatment and have an undetectable viral load.

HIV is a virus that damages the immune system. It’s spread when infected body fluids, such as blood, semen, vaginal fluid or mucus from inside the anus, get into the bloodstream. Most people in the UK who get HIV get it through sex, and there were 3,043 new HIV diagnoses in the UK in 2024.

There’s no cure, but with treatment most people with HIV can live a long and healthy life. Without treatment, HIV can eventually cause serious illnesses. This is known as late-stage or advanced HIV, or AIDS. Read more in “The stages of HIV explained”

Anal sex carries the highest risk of HIV from sex, especially for the receptive partner. HIV can get into the body through the thin lining of the rectum. The insertive partner can get HIV through the opening at the tip of the penis, the foreskin, or cuts or sores on the penis.

UK estimates for a single act with someone who has HIV and isn’t on effective treatment are:

• receptive anal sex with ejaculation: 1 in 65
• receptive anal sex without ejaculation: 1 in 170
• insertive anal sex, not circumcised: 1 in 161
• insertive anal sex, circumcised: 1 in 909

Read more in “Is unprotected anal sex dangerous?”

With someone who has HIV and isn’t on effective treatment, the estimated risk from a single act of vaginal sex is 1 in 1,000 for the receptive partner and 1 in 1,219 for the insertive partner. That’s low, but it isn’t no risk. In England in 2024, heterosexual men and women made up about half of all new HIV diagnoses.

The risk is higher if either partner has another STI, such as Syphilis, Herpes, Chlamydia or Gonorrhoea.

The risk from giving or receiving oral sex is very low, estimated at less than 1 in 10,000 per act. It can be higher if someone ejaculates in the mouth of a person with mouth ulcers or bleeding gums, or if either partner has genital sores or another STI.

Other STIs, like Gonorrhoea, Chlamydia and Syphilis, spread much more easily through oral sex. Read more in “Can you get HIV from oral sex?”

HIV can be passed on by sharing sex toys with someone who has a detectable viral load. HIV doesn’t survive long outside the body, but to lower the risk of HIV and other STIs, wash sex toys after each use and cover them with a new condom for each person. Read more in “Can you get an STI from a sex toy?”

Needles

If the other person has HIV and isn’t on effective treatment, sharing needles, syringes or other injecting equipment, including during chemsex, carries an estimated risk of 1 in 149 each time. A needlestick injury, for example in a healthcare setting, carries a risk of about 1 in 333.

Blood transfusions

In the UK, every blood donation is tested for HIV, and the risk of getting HIV from a transfusion is very low. The chance of a donation carrying an infection that testing misses is estimated at less than one in a million, and no infections from transfusions were confirmed in the UK in 2025.

Pregnancy, birth and breastfeeding

Without treatment, HIV passes from mother to baby during pregnancy, birth or breastfeeding in 15% to 45% of cases. With treatment, it’s rare. In England, the rate was 0.3% for babies born in 2020 and 2021, and there were no cases among women who were on treatment from conception and had an undetectable viral load.

U=U doesn’t apply to breastfeeding, so the risk isn’t zero. UK guidelines recommend formula feeding, which removes the risk, but say women with an undetectable viral load who choose to breastfeed should be supported to do so.

• Kissing: you can’t get HIV from kissing. The US Centers for Disease Control and Prevention notes a very small number of cases linked to deep kissing where both partners had sores or bleeding gums.
• Biting: the few reported cases involved severe bites with deep wounds and blood. UK estimates put the risk at less than 1 in 10,000.
• Spitting: no risk. HIV isn’t passed on through saliva.

You also can’t get HIV from hugging, shaking hands, or sharing toilet seats, food, drinks, cups or cutlery. Read more in “How much saliva is needed to transmit HIV?” and “Can you get an STD from a human bite?”

The risk is higher if:

• the person with HIV isn’t on treatment, or has a high viral load
• either of you has another STI
• alcohol or drugs lead to sex without a condom or sharing needles

The risk is lower, or zero, with:

• U=U (undetectable equals untransmittable): someone on effective treatment with an undetectable viral load can’t pass HIV on through sex. It usually takes around 6 months of treatment to become undetectable.
• Condoms: the most effective protection against HIV and other STIs.
• PrEP: medicine taken before sex to prevent HIV. Taken daily and correctly, it’s around 99% effective.
• PEP: emergency HIV medicine after a possible exposure. It should be started as soon as possible, preferably within 24 hours, and isn’t recommended after 72 hours. If you think you need it, get urgent medical care straight away.

Read more in “What is PEP and how does it work?”

HIV tests need time to give a reliable result. A lab blood test for HIV antibodies and the p24 antigen is reliable from 45 days after a possible exposure, and a rapid or self-test from 90 days. If you took PEP, test at least 45 days after finishing the course.

Better2Know offers:

• HIV 4th Generation: a blood test for HIV 1, HIV 2 and the p24 antigen from 28 days after sex, with results in 1 day. If you test before 45 days, a negative result needs a repeat test. You can book it at one of our clinics or order an HIV home test kit.
• Full Screen: tests for 7 infections, including HIV, Syphilis, Chlamydia and Gonorrhoea, from 28 days after sex, with results in 3 days (5 days for the home 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.

Can you get HIV from one time?

Yes, it’s possible, but for most types of sex it’s unlikely from a single act. With someone who has HIV and isn’t on effective treatment, the estimated risk from one act of receptive anal sex is 1 in 90, and from receptive vaginal sex 1 in 1,000.

Can you get HIV if they didn’t ejaculate?

Yes. The risk is lower, but it isn’t zero. For receptive anal sex with someone who has HIV and isn’t on effective treatment, UK estimates are 1 in 65 with ejaculation and 1 in 170 without. Read more in “Can you pass on or catch an STI without ejaculation?”

How soon can a test detect HIV?

A lab test for HIV antibodies and the p24 antigen is reliable from 45 days after a possible exposure. You can test sooner, but a negative result will need repeating. Read more in “How soon can HIV be detected by a blood test?”

The risk of HIV varies a lot depending on what happened. Anal sex and sharing needles carry the highest risks, while oral sex, biting and kissing carry very little or none. Condoms, PrEP and treatment that keeps HIV undetectable all protect you, and PEP can help after a recent risk.

If you’re worried, book an HIV 4th Generation test at a clinic near you or order an HIV home test kit from 28 days after sex. 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 26 September 2025 and was last updated on 30 September 2026.

Medical review. This article was medically reviewed by Dr Steve Chapman, Doctor with a wealth of clinical experience in the field of STIs, on 29 October 2025. It is general information and not a substitute for personal medical advice.

Sources

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