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HIV can pass through blood, semen and pre-seminal fluid, vaginal fluid, rectal fluid or breast milk when an infectious fluid reaches a mucous membrane, damaged tissue or the bloodstream. Routes include anal or vaginal sex, shared injection equipment, pregnancy, birth and breastfeeding. Maintaining a viral load below 200 copies/mL on ART prevents sexual transmission.[1][5][11]
Route 1: sexual contact
Anal and vaginal sex are the main sexual routes of HIV transmission. Either partner can acquire HIV when effective prevention is absent, with a higher baseline risk for the receptive partner. The exposure and prevention measures matter; a demographic label does not determine an individual’s risk.[5][1][10]
CDC’s historical baseline estimates per 10,000 exposures to a partner with HIV are 138 for receptive anal sex, 11 for insertive anal sex, 8 for receptive vaginal sex and 4 for insertive vaginal sex. Eight per 10,000 is about 1 in 1,250. These figures do not describe sex with a partner maintaining viral suppression or the protection from correctly used PrEP. Oral sex has little to no HIV risk, and a precise per-act estimate is not available.[11][3][9][10]
Route 2: shared injection equipment
Sharing needles or syringes can transfer another person’s blood. Cookers, filters and water can also become contaminated and should not be shared. CDC’s estimate of 63 transmissions per 10,000 exposures to a source with HIV applies specifically to needle sharing; it is not a measured rate for every item of equipment.[1][4][3][5]
Reused or improperly sterilized tattoo or piercing equipment can expose people to blood-borne infections. Effective HIV treatment may reduce transmission through shared injection equipment, but there is no established zero-risk threshold for that route. U=U should not be used as a reason to share equipment.[11][5][4]
Route 3: pregnancy, birth, and breastfeeding
HIV can pass during pregnancy, birth or breastfeeding. A 2014 review estimated 22.6% transmission during pregnancy and delivery without preventive treatment; that historical estimate is not a prediction for a pregnancy with modern HIV care.[1][9]
With effective ART and coordinated pregnancy, delivery and infant care, perinatal transmission can be reduced to 1% or less. Infant medicine is tailored to exposure risk: current NIH guidance recommends two weeks of zidovudine for infants meeting low-risk criteria, with different regimens or durations for others. Breastfeeding with sustained suppression carries a risk below 1%, but not zero; properly prepared formula or pasteurized banked donor milk eliminates HIV transmission through breastfeeding.[12][13][14][4][9]
Route 4: blood and occupational exposure
Transfusion with HIV-containing blood is the single highest-risk exposure on CDC's list — 9,250 per 10,000[3]. It is also, in the United States, essentially historical: NIH notes that strict blood screening has cut U.S. transfusion risk to less than one in a million[5].
CDC’s historical estimate for a percutaneous needlestick involving a source with HIV is 23 per 10,000 exposures (0.23%, roughly 1 in 435). Occupational transmission is very rare, and an exposure should be reported immediately for PEP assessment. Rare nonsexual blood exposures require a route into the body; ordinary contact with intact skin does not provide that route.[3][4][7][5]
What does not transmit HIV — and what U=U means
HIV is not spread by mosquitoes or other insects, air, hugging, shared toilets or dishes, or saliva without blood. Ordinary kissing does not transmit HIV. A significant exposure to visibly bloody fluid through a mucous membrane, damaged skin or a penetrating injury warrants individual assessment; that is a blood exposure, not transmission through saliva itself.[15][2][8][10][3]
U=U is established: maintaining HIV RNA below 200 copies/mL on ART prevents sexual transmission. A laboratory may detect HIV below that threshold without changing this conclusion. NIH advises an additional prevention method for at least the first six months after starting ART and until a result below 200 is documented, followed by continued treatment and monitoring.[11][6]
Related questions
Can mosquitoes spread HIV?
No. HIV is not transmitted by mosquitoes, ticks or other insects.[2]
Is kissing safe?
Does “undetectable” mean zero, or just very low?
Maintaining HIV RNA below 200 copies/mL on ART prevents sexual transmission. The limit for a laboratory report to say “undetectable” varies by test and is usually lower. Continued treatment and viral-load monitoring are important.[11]
Can someone with HIV have a baby who doesn't have HIV?
Yes. Effective ART and coordinated pregnancy, delivery and infant care can reduce perinatal transmission to 1% or less. Infant medicines depend on exposure risk; they are not a universal four-to-six-week course. Breastfeeding requires a separate discussion because suppression reduces that risk but does not eliminate it.[12][13][14]
Related from RiseUpToHIV
References & Sources
- CDC — How HIV Spreads. The fluids that carry HIV, the routes of entry, and perinatal transmission. ↩ ↩ ↩ ↩ ↩ ↩
- NIH HIVinfo — Understanding How HIV Is Transmitted; routes that do and do not transmit HIV. Source. ↩↩ ↩
- CDC — HIV Risk and Prevention Estimates. Per-10,000 estimates for sex, needle sharing, transfusion, and needlestick. ↩ ↩ ↩ ↩ ↩ ↩
- CDC — How HIV Spreads; injection equipment, treatment and perinatal transmission. Source. ↩↩↩↩↩↩
- NIH HIVinfo — Understanding How HIV Is Transmitted. Share of diagnoses from sexual contact, transfusion safety, and rare blood routes. ↩ ↩ ↩ ↩ ↩ ↩ ↩
- NIH — Undetectable equals untransmittable. Federal U=U statement and the trials behind it. ↩ ↩
- HIV.gov — Post-Exposure Prophylaxis (PEP). PEP after occupational or other exposures; workplace transmission is extremely rare. ↩
- WHO — HIV and AIDS fact sheet. Global guidance that HIV is not spread by kisses, hugs, or sharing food. ↩
- Patel et al. (2014) — Estimating per-act HIV transmission risk: a systematic review; historical baseline estimates. Source. ↩↩↩
- CDC — About STI Risk and Oral Sex; little to no HIV risk and limits of per-act evidence. Source. ↩↩↩
- NIH ARV Guidelines — Treatment as Prevention; sustained viral load below 200 copies/mL prevents sexual transmission. Source. Checked September 21, 2026. ↩ ↩ ↩ ↩ ↩
- NIH Perinatal Guidelines — Antiretroviral Management of Infants; risk-based regimens and durations. Source. Checked September 21, 2026. ↩ ↩
- NIH Perinatal Guidelines — Preventing HIV Transmission During Infant Feeding. Source. Checked September 21, 2026. ↩ ↩
- NIH Perinatal Guidelines — Intrapartum Care for People With HIV. Source. Checked September 21, 2026. ↩ ↩
- CDC 2025 nPEP Guidelines, Appendix A — exposure-specific recommendations, including saliva and visible blood. Source. Checked September 21, 2026. ↩ ↩
Community publications like POZ, Positively Aware, and TheBody inform framing and lived-experience context on RiseUpToHIV. Every clinical, epidemiological, or public-health claim above is anchored to a primary source.