Circumcision and HIV: Why the Foreskin Matters, and What the 60–70% Figure Really Means

最終更新日： 2026年8月15日

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Worry about HIV after unprotected sex is one of the most distressing things men bring to my clinic. Everyone knows condoms protect against HIV. Fewer people know that circumcision has a protective effect too — and fewer still know exactly what that protection covers and what it does not.

If you are reading this because a possible exposure happened in the last few days, start here rather than with the rest of the article. Post-exposure prophylaxis (PEP) is a course of antiretroviral medication that can substantially reduce the chance of infection, but it has to be started as soon as possible and within 72 hours of the exposure — the earlier the better. Go to an emergency department or an infectious diseases service now; at Bangkok Hospital, HIV testing, PEP and PrEP are handled by Infectious Diseases rather than by the urology clinic. Nothing on this page is useful after an exposure has already happened: circumcision is a long-term measure and does nothing retrospectively.

Circumcision has clear medical value in its own right — for phimosis, where the foreskin cannot be retracted, and for recurrent bacterial infection of the foreskin. What surprises most patients is the HIV finding on top of that.

Several high-quality studies report a 60–70% reduction in HIV transmission in circumcised compared with uncircumcised men. That result is what pushed researchers to work out why — and the answer is that the foreskin itself is a major route of entry.

Read that figure carefully, though. It comes from trials of female-to-male transmission during vaginal sex. It does not describe protection for the female partner, and the evidence does not support the same protection for men who have sex with men, where the transmission route is different. It is a reduction in risk, not a shield — and it makes no difference at all to transmission through blood or needles.

Three reasons the foreskin is the weak point

1. HIV’s target cells are concentrated there. The primary target for HIV is the Langerhans cell, a type of white blood cell that is particularly dense in the inner foreskin. Circumcision removes that tissue — and with it, the highest concentration of cells the virus is looking for.
2. The skin barrier there is thinner. The inner foreskin has fewer keratinised protective layers than the rest of the penile skin, making it far more permeable to the virus. It is also prone to micro-abrasions and small tears during sex, and each of those is a direct entry point.
3. The local bacteria make things worse. The normal flora living under the foreskin produce pro-inflammatory substances that draw immune cells to the area — bringing HIV and its target cells into easier contact and amplifying the risk further.

Taken together, these explain why the foreskin punches so far above its weight in HIV transmission, and why removing it changes the odds so much.

None of this replaces a condom. Circumcision reduces risk substantially; a condom used consistently reduces it far more, and covers the situations circumcision does not. The sensible position is to treat circumcision as one layer among several — alongside condoms, regular STI screening and knowing your partner’s status — rather than as a reason to relax about any of them. If you want to weigh it up for yourself, that is a conversation to have with a urologist, and the surgical techniques are compared here.

It is also worth saying plainly that circumcision is an operation, not a vaccine. It carries the usual surgical risks of bleeding, infection and an imperfect cosmetic result, and there is a healing period of several weeks during which sex should be avoided — and during which the wound itself may make transmission easier rather than harder. Anyone choosing it for protective reasons should weigh those against a measure that only shifts the odds.

医学的、予防的、または個人的な理由で成人割礼を検討されている場合は、ソアラウィー・ウィーラソポン医師がバンコク病院本社で専門医の診察を行っています。. 診療をご予約. サミティウェート・シーラチャ病院のご予約は、泌尿器科（電話番号：）までお問い合わせください。 088-022-1445.

Bangkok Hospital also runs a Telemedicine service for patients who cannot attend in person, including international patients — arrange it in advance by email to the Urology department at bhquro@bdms.co.th. Samitivej Sriracha is in-person only. A recent possible HIV exposure is not a telemedicine matter: that needs same-day assessment in person.

割礼とHIV予防に関するよくある質問

免責事項 This content is written and reviewed by Dr. Soarawee Weerasopone, a board-certified urologist at Bangkok Hospital Headquarters. It is intended for educational purposes only and does not constitute medical advice. Circumcision reduces but does not eliminate the risk of HIV transmission and is not a substitute for condoms or other preventive measures. A possible HIV exposure within the last 72 hours is time-critical and needs immediate in-person assessment by an emergency or infectious diseases service. No medical advice, diagnosis or prescription is provided through personal messaging channels. Always consult a qualified healthcare professional before starting any medical treatment.