What counts as an HIV risk, and what doesn't?

HIV is harder to catch than most people fear. A calm, factual guide to what is a real risk, what isn't, when to test, and what to do next.

If you’re reading this because you’re worried about something that happened, take a breath. HIV is harder to catch than most people think, and whatever happened, there are clear next steps.

One thing first: if the event was in the last 72 hours and it involved sex without a condom or a shared needle, go to the urgent page now. There is emergency medicine called PEP, and time matters. You can read the rest afterwards.

How HIV is actually passed on

HIV is only found in enough quantity to infect someone in a few body fluids. The US Centers for Disease Control and Prevention (CDC) lists them:

• blood
• semen and pre-seminal fluid (“pre-cum”)
• rectal fluids
• vaginal fluids
• breast milk

And the fluid has to get into the other person’s body. In the CDC’s words, these fluids “must come into contact with a mucous membrane or damaged tissue or be directly injected into the bloodstream”. Mucous membranes are the soft linings inside the rectum, vagina, the opening of the penis, and the mouth.

Both things have to be true: the right fluid, and a way in. That is why most everyday contact carries no risk at all.

What is a real risk

• Anal or vaginal sex without a condom or PrEP, with someone who has HIV and isn’t on effective treatment.
• Sharing needles, syringes or other injecting equipment.
• From a parent to a baby during pregnancy, birth or breastfeeding, if the parent isn’t on treatment.

These are by far the most common ways HIV is passed on.

How big is the risk?

The CDC publishes estimates of the chance of getting HIV from one exposure, when the other person has HIV, is not on treatment, and no condom or PrEP is used:

Two things about this table. First, these are averages. The chance is higher if the person with HIV was infected very recently, or if either person has another STI. Second, even the highest figure means the large majority of single exposures don’t lead to infection. That isn’t a reason to ignore a real risk. It is a reason not to assume the worst.

What lowers the risk to zero, or close to it

• The other person is on treatment and undetectable. Then there is no risk from sex at all. This is U=U.
• You take PrEP. About 99% effective for sex when taken as prescribed.
• Condoms, used consistently.
• PEP, started within 72 hours of an exposure.

What is not a risk

The CDC is explicit that HIV is not passed on by:

• saliva, tears or sweat
• closed-mouth kissing, hugging, shaking hands, or sharing a bed
• sharing toilets, towels, dishes, glasses or food
• mosquitoes, ticks or other insects
• touching surfaces. HIV does not survive long outside the body
• spitting
• donating blood

The ones people worry about most

• Oral sex. Low risk. It can be slightly higher if there’s ejaculation in the mouth together with mouth ulcers, bleeding gums or genital sores, but overall transmission this way is extremely rare.
• Deep kissing. Virtually no risk, unless both people have sores or bleeding gums and blood is exchanged.
• Fingering, handjobs, mutual masturbation. No realistic route for the virus to get in.
• A condom that stayed on and didn’t break. That is protected sex.
• A condom that broke or slipped off during anal or vaginal sex. That is a real exposure. If it was in the last 72 hours, ask about PEP.
• Tattoos and piercings. The CDC knows of no documented cases, though it is possible in theory if equipment or ink carries blood from someone with HIV. Licensed studios using new needles are not a concern.
• Biting. Negligible. The very rare cases on record involved severe injuries with blood.

When should I test?

No test can detect HIV straight away. The gap between exposure and when a test can pick it up is called the window period, and it depends on the test. According to the CDC:

So a negative result a week after the event doesn’t tell you about that event yet. A clinic can tell you which test they use and when to come back. A negative result after the window period has passed is reliable.

What to do now

1. Within 72 hours of a real risk: go to the urgent page and get assessed for PEP.
2. After 72 hours: book an HIV test for the right time using the table above, and get a full STI check while you’re there. Other STIs are far more common than HIV and mostly easy to treat.
3. If this keeps happening: ask about PrEP.
4. If you’re not sure whether what happened counts: ask a clinic. They hear these questions every day and will not judge you.

If you’ve tested negative after the window period and the worry won’t go away, that is common, and it is worth talking to someone about the anxiety itself. It’s a health concern in its own right, and clinics and helplines can point you to support.

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Sources

Checked 19 September 2026.

• CDC, How HIV spreads
• CDC, HIV risk and prevention estimates
• CDC, Getting tested for HIV

Where To Test is a directory, not a clinical service. Rules and prices change; every figure here links to its source and the date we checked. Spotted something out of date? Use “Something wrong? Tell us” on any clinic page.