Short answer
Anal sex transmits the full STI range with the highest per-act HIV efficiency of any sex type. Chlamydia, gonorrhea (frequently silent rectally), syphilis, herpes, HPV (warts and cancer risk), plus intestinal infections in some networks.
The same act needing the most protection also gets tested the least. Closing both gaps (condoms plus ample lubricant plus PrEP plus rectal screening) is the entire message of this guide.
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See Tests & Prices →Risk profile. Why this route tops the ladder
- HIV: highest per-act transmission risk, especially receptive. The rectal lining is thin, tears microscopically during intercourse, and offers efficient bloodstream entry.
- Chlamydia and gonorrhea: frequent silent rectal infections (carriers without symptoms sustaining transmission for months).
- Syphilis, herpes, HPV: contact-driven transmission with anal warts and (for high-risk groups) anal cancer risk under screening guidance.
- Intestinal infections (shigella, LGV-associated proctitis in some MSM networks. Non-STI harms through the identical route).
Anatomy explains the ranking; behavior (barriers, lubricant, screening) overcomes it.
The protection stack. Every layer doing its job
- External condoms every time (or internal condoms with technique adjustments. One barrier per act, never both).
- Generous water- or silicone-based lubricant (friction causes the microtears admitting virus. The rectum does not self-lubricate, so adequacy is non-negotiable; reapply during extended acts).
- HIV PrEP for ongoing risk (daily, event-driven where eligible, or injectable. Matched to life patterns).
- HPV vaccination (anal cancer prevention upstream).
- Rectal STI screening on schedule (detection closing what barriers miss).
Lubricant technique detail at Using Lubricants with Condoms; rectal sampling detail at Rectal STI Testing: How It Works.
Testing after anal exposure. Request by name
- Rectal NAAT swabs plus standard blood panels (HIV, syphilis, hepatitis by risk). Genital urine tests alone miss rectal infections completely.
- Disclose anal exposures explicitly so sampling covers them (clinicians cannot swab sites they are not told about. State plainly, heard routinely).
- Self-collected rectal swabs are an option in many clinics (private, instructed, equally accurate. Ask explicitly).
Throat swabs join where oral-anal contact occurred; genital sampling completes the multi-site set.
When to seek care
For rectal pain, discharge, or bleeding; after condomless anal exposure (PEP evaluation when HIV risk applies); and for routine rectal screening with ongoing exposure.