UAI stands for unprotected anal intercourse. It refers to anal sex without a condom and has been widely used in public health research, HIV prevention campaigns, and sexual health discussions since the early days of the HIV/AIDS epidemic in the 1980s. If you came across this term in a health context, here’s what it means and why it matters.
Why the Term Exists
UAI became a standard abbreviation in medical and public health literature because anal intercourse without a condom carries the highest per-act risk of HIV transmission among sexual behaviors. Researchers needed a shorthand to study and communicate that risk clearly. For decades, “any UAI” served as the primary measure of HIV-related sexual risk in studies, particularly among men who have sex with men.
The Shift to “Condomless Anal Intercourse”
You may also see the newer term CLAI, or condomless anal intercourse. The CDC recommended this language change because the word “unprotected” is no longer fully accurate. Today, people can be protected from HIV during condomless sex through other means: PrEP (a daily or on-demand medication that reduces HIV risk from sex by about 99%), or an HIV-positive partner maintaining an undetectable viral load through treatment, which eliminates the risk of sexual transmission entirely. This concept is known as U=U, or undetectable equals untransmittable.
In other words, anal sex without a condom is not automatically “unprotected” the way it was understood in the 1980s and 1990s. The terminology shifted to reflect that reality. Both UAI and CLAI still appear in research and health education, but CLAI is becoming the preferred term in newer publications.
HIV Transmission Risk During UAI
Without any form of prevention (no condoms, no PrEP, no HIV treatment), the per-act HIV risk during anal sex depends on your role. The receptive partner (bottom) faces the higher risk: roughly 1 in 72 per act, or about 138 per 10,000 exposures, when the insertive partner is HIV-positive. The insertive partner (top) has a lower but still meaningful risk of about 1 in 909 per act.
These numbers represent averages across many encounters. Individual risk can be higher or lower depending on factors like the presence of other sexually transmitted infections, whether ejaculation occurs, and the viral load of the HIV-positive partner. Rectal tissue is thin and rich in immune cells that HIV targets, which is why receptive anal sex carries more risk than most other sexual activities.
Other STI Risks
HIV gets the most attention in discussions of UAI, but condomless anal sex also increases exposure to other infections. Rectal chlamydia has a prevalence of about 9% in screened populations, and rectal gonorrhea around 5%, with somewhat higher gonorrhea rates (6.1%) among men who have sex with men. These infections are often asymptomatic, meaning you can carry and transmit them without knowing. Syphilis, HPV, and hepatitis are also transmitted through condomless anal contact.
PrEP protects against HIV but does nothing for these other infections. This is one reason public health messaging still encourages condom use even among people taking PrEP, and why regular STI screening (typically every three to six months for sexually active individuals) remains important regardless of HIV prevention strategy.
How Modern Prevention Changes the Picture
Three tools have fundamentally changed what UAI means in terms of actual risk:
- Condoms remain highly effective at reducing transmission of HIV and most STIs when used consistently.
- PrEP reduces HIV acquisition from sex by approximately 99% when taken as directed. It’s available as a daily pill or a long-acting injection given every two months.
- Treatment as prevention (U=U) means a person living with HIV who maintains an undetectable viral load through medication will not transmit HIV to sexual partners. This has been confirmed through large studies involving thousands of couples over years of follow-up with zero linked transmissions.
Because of these advances, researchers have argued that simply counting instances of “any condomless anal intercourse” no longer accurately captures someone’s actual HIV risk. A person on PrEP having condomless sex with a partner who has an undetectable viral load faces essentially zero HIV risk from that encounter, even though it would technically be classified as UAI. This is why the field has moved toward more nuanced ways of assessing risk rather than treating all condomless anal sex as equally dangerous.
Other Meanings of UAI
Outside of sexual health, UAI occasionally appears as an abbreviation in other contexts, such as the University of the Americas in Ecuador (Universidad de las Américas) or various institutional acronyms. In medical lab work, you might see the similar abbreviation uACR for urine albumin-creatinine ratio, a kidney function test, but that’s a different abbreviation. If you encountered UAI in a health or sex education context, the sexual health meaning is almost certainly what was intended.