What is the risk of HIV transmission during oral sex?

Risk of HIV Transmission Through Oral Sex

The risk of acquiring HIV from oral sex is extremely low, with the CDC estimating approximately 0.04% (4 per 10,000 exposures) for receptive oral sex (fellatio), making it substantially safer than vaginal intercourse (0.1–0.2%) or receptive anal intercourse (0.5–3%). 1

Quantified Transmission Risk

• Receptive oral sex (fellatio) carries a per-contact risk of approximately 0.04% when the partner's HIV status is unknown or positive 1
• Research data from prospective cohort studies confirm this low risk, with one study estimating 0.04% per-contact risk for receptive oral sex with HIV-positive or unknown serostatus partners 2
• A systematic review examining exclusively oral sex practitioners found zero HIV infections among 239 men who practiced only fellatio over 6 months, despite 98% having unprotected contact and 28% having HIV-positive partners 3
• The population-attributable risk for HIV from fellatio is estimated at only 0.10–0.31% even with multiple partners 3

Critical Risk-Enhancing Factors

While baseline risk is very low, specific conditions dramatically increase transmission probability and must be assessed:

High-Risk Scenarios Requiring PEP Consideration

• Ejaculation in the mouth delivers substantially higher viral inoculum than pre-ejaculate exposure 1
• Oral lesions, bleeding gums, or ulcers create direct entry points for HIV and markedly elevate risk 1
• High viral load in the source partner is the single most important amplifying factor 1, 4
• Concurrent STIs, particularly genital ulcerative diseases (herpes, syphilis), increase viral shedding and transmission probability 1, 4
• Trauma or bleeding during the act further elevates acquisition risk 1

Protective Factors

• Saliva contains multiple antiviral factors including lysozyme, defensins, thrombospondin, and secretory leucocyte protease inhibitor (SLPI) that reduce HIV viability 5
• Fewer CD4+ target cells in oral mucosa compared to rectal or vaginal tissue 5
• Presence of IgA antibodies in saliva provides additional protection 5
• Saliva not contaminated with blood contains HIV in much lower titers and constitutes negligible exposure risk 6

Post-Exposure Prophylaxis (PEP) Decision Algorithm

Initiate PEP immediately (ideally within 24 hours, no later than 72 hours) if:

1. Known HIV-positive source partner with ejaculation in mouth 1
2. Presence of oral lesions, bleeding gums, or trauma in the receptive partner 1
3. Source partner has high or unknown viral load 1
4. Visible blood in saliva during or after the exposure 6

PEP may be considered on case-by-case basis if:

• Source partner HIV status unknown but high-risk population (e.g., MSM, injection drug users) with ejaculation 6
• Multiple risk-enhancing factors present even without ejaculation 1

PEP is generally not indicated if:

• No ejaculation occurred AND no oral lesions/bleeding present 1
• Source partner is virally suppressed on antiretroviral therapy (reduces transmission risk by ~96%) 4
• Exposure occurred >72 hours ago (PEP effectiveness declines sharply) 1

PEP Regimen

• 28-day course of combination antiretroviral therapy using HAART regimens 6, 1
• Preferred regimens include efavirenz with lamivudine or emtricitabine plus zidovudine or tenofovir, or lopinavir/ritonavir-based combinations 6

Prevention Strategies for Ongoing Risk

• Pre-exposure prophylaxis (PrEP) should be offered to individuals with repeated high-risk oral exposures to HIV-positive partners 1
• Latex condoms during oral sex reduce exposure to seminal fluids 1
• Regular STI screening every 3–6 months for sexually active persons, as co-existing STIs amplify transmission risk 1
• Viral suppression in HIV-positive partners through antiretroviral therapy reduces transmission risk by approximately 96% across all exposure types 1, 4

Common Pitfalls to Avoid

• Do not dismiss oral sex as "zero risk"—documented cases of HIV transmission through oral sex alone have occurred, confirming biological plausibility 1
• Do not delay PEP initiation while awaiting source partner testing; start immediately if indicated and discontinue if source tests negative 6
• Do not overlook oral health assessment—bleeding gums from routine tooth brushing or flossing can create entry points 1
• Do not assume low risk means no testing needed—baseline and follow-up HIV testing at 6 weeks, 3 months, and 6 months post-exposure remains essential 6