HIV spreads only through specific body fluids — blood, semen, vaginal fluid, rectal fluid, and breast milk — passed during anal or vaginal sex, sharing needles, or from parent to child in pregnancy, birth, or breastfeeding. It does not spread through saliva, touch, toilet seats, or air. Condoms, PrEP, PEP, treatment-as-prevention, and regular testing all stop it.
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 |
You found this page searching for how HIV exposure and transmission actually work, so let's be precise. HIV (human immunodeficiency virus) attacks the body's immune system, and over time, if untreated, it wears down the cells that fight infection CDC. There's no cure, but with treatment people live long, healthy lives and don't pass the virus to partners. Knowing how it moves, and the many ways it doesn't, turns worry into a plan.
How HIV is actually transmitted
HIV needs a way into your bloodstream, and it can only get there through a handful of fluids that carry enough virus to do it: blood, semen (including pre-seminal fluid), vaginal fluid, rectal fluid, and breast milk CDC, How HIV Spreads. The virus doesn't survive long outside the body, so transmission requires those fluids reaching your bloodstream or a mucous membrane — the moist tissue lining the rectum, vagina, penis, or mouth. In real life, that happens a few ways.
Anal and vaginal sex
Sex is the most common route. During anal or vaginal sex, infected semen, vaginal fluid, or rectal fluid contacts the mucous membranes that line those tissues, and the virus crosses into the body. Receptive anal sex (being the bottom) carries the highest per-act risk because the rectal lining is thin and easily disrupted. The chemistry of the genital tract matters too. For a closer look at one factor, see the role of vaginal ph in hiv transmission risk. Any open sore or other STI raises the odds by giving the virus an easier doorway.
Sharing needles and injection equipment
Blood carries a very high concentration of HIV, so sharing needles, syringes, or any drug-injection gear passes it directly into the bloodstream. Even small amounts of leftover blood in shared equipment can transmit the virus. Screened blood donation in the US is safe, and you cannot get HIV by donating blood.
From parent to child (perinatal)
A pregnant person with HIV can pass it to the baby during pregnancy, delivery, or breastfeeding. With antiretroviral treatment 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. HIV screening is a routine part of prenatal care for this reason.
Timing matters. HIV is most contagious during acute infection, the first few weeks after someone catches it. About 90% of people get flu-like symptoms two to four weeks in, exactly when the viral load peaks above a million copies per milliliter StatPearls. A person may not yet know they're positive during this window, which is when so much transmission happens.
How HIV is NOT transmitted
A lot of needless fear lives here, so let's be blunt. HIV does not survive long outside the human body and cannot spread through everyday contact. You cannot catch HIV from:
- Saliva, kissing, sneezing, coughing, or shared drinks and utensils — saliva alone does not transmit HIV.
- Toilet seats, doorknobs, gym equipment, or any surface someone touched.
- Towels, bedding, or sharing clothes.
- Hugging, shaking hands, or other casual skin-to-skin contact.
- Food prepared by someone with HIV.
- Mosquitoes, ticks, or any insect bites.
- Swimming pools, hot tubs, water, or air.
- Donating blood at a licensed center.
If a route isn't on the transmission list above — blood, semen, vaginal fluid, rectal fluid, or breast milk reaching the bloodstream or a mucous membrane — it carries no real risk. Sharing a bathroom or a coffee with someone who has HIV is completely safe.
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. Risk isn't spread evenly. The groups carrying the highest burden include gay and bisexual men and other men who have sex with men, people who inject drugs, and partners of people with HIV who aren't virally suppressed. Geography matters too, with diagnosis rates clustering in the South and the capital, led by Washington DC, Georgia, Florida, and Louisiana. Anyone having sex with new or multiple partners, or who has another STI, has elevated risk and benefits from regular testing.
Reducing the risk
The CDC's prevention toolkit works, and most people use a combination CDC, PrEP. Here's how the main tools stack up.
| Tool | Who it's for | How it works |
|---|---|---|
| Condoms | Everyone having sex | Block fluid contact during anal and vaginal sex; also cut other STIs. |
| PrEP (daily pill or shot) | HIV-negative people at ongoing risk | Medicine taken before exposure; reduces sexual HIV risk by about 99% when taken as prescribed. |
| PEP | After a possible exposure | A 28-day emergency course started within 72 hours. |
| Treatment-as-prevention (U=U) | People living with HIV | An undetectable viral load means zero transmission to partners. |
| Regular testing | Everyone | Finds infection early so treatment and prevention can start. |
PrEP is for HIV-negative people exposed through sex or injection drug use. Daily oral options are Truvada and Descovy, and the long-acting injectable cabotegravir (Apretude) is given as two starter doses a month apart, then every two months. Descovy isn't approved for people at risk through receptive vaginal sex, while Truvada covers all routes. PrEP requires a confirmed negative HIV test before starting plus regular follow-up, because starting it with undiagnosed HIV risks drug resistance. Twice-yearly injectable lenacapavir produced zero infections among women in a major trial WHO.
U=U — undetectable equals untransmittable. A person on treatment who stays virally suppressed will not transmit HIV to sex partners. Across the PARTNER studies, mixed-status couples logged tens of thousands of condomless sex acts with zero linked transmissions while the positive partner was undetectable Lancet, PARTNER. Most people reach undetectable within six months of starting treatment CDC.
If you may have been exposed
If you think you were exposed in the last three days, this is urgent. PEP can prevent infection but must start within 72 hours, so go to urgent care or an ER today CDC, PEP. If the exposure was longer ago, the next step is testing on the right timeline — read when to test after exposure and learn how the different hiv testing methods fit your window.
When to see a clinician
The USPSTF gives HIV screening its strongest recommendation: everyone ages 15 to 65 should be tested at least once, and people at higher risk should repeat at least yearly USPSTF, Grade A. Beyond routine screening, see a clinician promptly if you've had a possible exposure, if you have flu-like symptoms after a recent risk, if you want to start PrEP, or if you're pregnant and don't know your status. Symptoms can't confirm or rule out HIV — only a test can. You can get tested quickly and confidentially, and starting treatment early gives a 20-year-old a life expectancy approaching the general population's Lancet HIV.