HIV spreads only when specific body fluids — blood, semen, vaginal fluid, rectal fluid, or breast milk — from a person with the virus enter another person's bloodstream. In practice that means anal or vaginal sex, sharing needles or injection equipment, and passing it from parent to baby during pregnancy, birth, or breastfeeding CDC, How HIV Spreads. Your risk depends heavily on the activity.
in 2023
≈723,000 — U=U
| Item | Value |
|---|---|
| New diagnoses | 38,800 — in 2023 |
| Living with HIV | 1.12 million |
| Virally suppressed | ~65% — ≈723,000 — U=U |
| On PrEP | 381,000 |
How HIV is actually transmitted
HIV is a virus that attacks the immune system, and it can't do that until it reaches living cells inside the body. It doesn't survive long on air, surfaces, or in water, so it needs a direct route in — usually a mucous membrane (the lining of the rectum, vagina, penis, or rarely the mouth) or a break in the skin. Only five fluids carry enough virus to matter: blood, semen, vaginal fluid, rectal fluid, and breast milk CDC, About HIV. Sweat, tears, urine, and saliva on their own don't transmit it.
Risk by activity — the per-act numbers
Not all exposures carry the same odds. The lining of the rectum is thin and easily injured, which is why receptive anal sex is the highest-risk sexual act. Sharing injection equipment puts virus straight into the bloodstream. Oral sex carries very low risk. Use this table to compare relative danger by route, but remember a single exposure can be enough.
| Activity | Relative HIV risk per exposure | Why |
|---|---|---|
| Sharing needles / injection equipment | Very high | Blood goes directly into the bloodstream |
| Receptive anal sex (bottom) | Highest sexual risk | Thin, fragile rectal lining that tears easily |
| Insertive anal sex (top) | Lower than receptive, still meaningful | Virus enters through the urethra and foreskin |
| Receptive vaginal sex | Moderate | Large mucosal surface exposed to semen |
| Insertive vaginal sex | Lower than receptive | Exposure through the urethra/foreskin |
| Oral sex | Very low | Saliva and an intact mouth lining are poor entry points |
| Mother to baby (untreated) | Significant — but preventable | Pregnancy, delivery, or breast milk |
One detail changes all of these odds dramatically: the viral load of the person with HIV. During acute (very early) infection, about 9 in 10 people get flu-like symptoms roughly two to four weeks after exposure — exactly when the viral load peaks above a million copies per milliliter and the virus is most contagious StatPearls, HIV. At the other extreme, a partner on treatment with an undetectable viral load doesn't transmit HIV at all, which I'll come back to.
How HIV is NOT transmitted
This is where a lot of needless worry lives, so let me be direct. HIV doesn't survive well outside the body, and casual contact simply doesn't move it from one person to another. You can't catch HIV from any of these:
- Toilet seats, doorknobs, gym equipment, or other surfaces.
- Sharing towels, dishes, cups, or utensils.
- Hugging, shaking hands, or being near someone who has HIV.
- Saliva, tears, or sweat — kissing alone does not transmit HIV.
- Food prepared by someone with HIV.
- Mosquitoes, ticks, or other insect bites.
- Swimming pools, hot tubs, or drinking water.
- Donating blood (sterile, single-use needles are used).
If a route isn't on the transmission list above, it's not a route. Saliva, in particular, contains enzymes that inactivate the virus, so closed-mouth and even deep kissing aren't risks on their own.
Who's at higher risk
About 38,800 people were newly diagnosed with HIV in the US in 2023, and roughly 1.12 million are living with it CDC AtlasPlus, 2023. The burden isn't evenly spread. Gay and bisexual men and other men who have sex with men carry the highest share of new diagnoses, largely because receptive anal sex is the most efficient sexual route. People who inject drugs and share equipment are at high risk through blood. Diagnosis rates also cluster geographically — highest in 2023 in Washington DC, Georgia, Florida, and Louisiana — so where you live and your partners' status both shape your exposure. For a fuller picture of who's affected, see our hiv facts & statistics - who's been affected by hiv.
Mother-to-baby transmission and what it means for newborns
HIV can pass to a baby during pregnancy, labor, or breastfeeding through blood, vaginal fluid, or breast milk. The encouraging part is how preventable this has become: with antiretroviral treatment (ART) during pregnancy and labor plus a short course of medicine for the newborn, the risk of passing HIV to the baby drops to less than one percent. Starting a pregnant person on treatment early protects both their health and the baby's. If you're navigating this, our guides on whether is early hiv treatment in babies safe and effective and how earlier hiv treatment can help prevention work walk through the specifics.
Reducing the risk
The CDC's core toolkit is condoms, PrEP, PEP, treatment-as-prevention (U=U), and regular testing CDC, PrEP. Used together they make HIV one of the most preventable serious infections.
- Condoms block the fluids that carry HIV and also cut your risk of other STIs.
- PrEP (pre-exposure prophylaxis) is daily or injectable medicine for HIV-negative people; taken as prescribed it reduces HIV risk from sex by about 99% and from injection drug use by at least 74%. Daily options are Truvada and Descovy; the long-acting shot is cabotegravir (Apretude). Note Descovy isn't approved for people at risk through receptive vaginal sex.
- Treatment-as-prevention (U=U) — a partner on ART with an undetectable viral load won't transmit HIV.
- Not sharing needles or any injection equipment removes the blood route.
- Regular testing so anyone with HIV can start treatment and protect partners.
On U=U, the data is genuinely settled. Across the PARTNER studies, mixed-status couples had tens of thousands of condomless sex acts with zero HIV transmissions when the partner with HIV had a viral load under 200 copies per milliliter PARTNER, Lancet. That's why undetectable equals untransmittable — treatment is both health and prevention CDC, U=U. Newer prevention keeps raising the bar, too: twice-yearly injectable lenacapavir produced zero infections among women in the PURPOSE 1 trial, the strongest HIV-prevention result to date WHO, lenacapavir.
If you think you've just been exposed
This is a same-day decision, not a wait-and-see one. PEP (post-exposure prophylaxis) can prevent infection, but it must start within 72 hours of the exposure and is taken daily for the following weeks — go to urgent care or an ER right away CDC, PEP. After that window, focus shifts to testing on the right timeline; see when to test after exposure for what to do and when.
When to see a clinician
The USPSTF gives HIV screening its top recommendation (Grade A): everyone ages 15 to 65 should be tested at least once, and people at increased risk should repeat it at least yearly USPSTF, Grade A. Book a visit promptly if you've had a possible exposure, if you've shared injection equipment, if you have flu-like symptoms in the weeks after a risk, or if you're starting or already on PrEP and need follow-up. You can get tested discreetly, and modern HIV — caught and treated early — is a manageable, long-term condition with a near-normal life expectancy Lancet HIV.