Circumcision is the removal of the foreskin from the penis. It changes HIV risk in some situations and not others, so it helps to be precise about who it protects.

What the trials found

Randomized trials found that men who were circumcised were much less likely to get HIV through vaginal sex than men who weren’t, roughly halving their risk or better. The WHO lists being circumcised as one of the ways men can lower their risk of HIV. The calculator lowers a circumcised man’s estimate by 50% when he is the insertive partner.

For a man having vaginal sex with a woman who has HIV and isn’t on treatment, the estimated risk per act is 0.04% (about 1 in 2,500) if he isn’t circumcised and 0.02% (about 1 in 5,000) if he is.

With a partner whose status you don’t know, the numbers are lower, but the effect is the same. In South Africa, for example, the estimate for one act is 0.0023% (about 1 in 44,000) uncircumcised and 0.0011% (about 1 in 89,000) circumcised.

What circumcision doesn’t do

  • It isn’t full protection. A circumcised man can still get HIV. Condoms, PrEP (pre-exposure prophylaxis) and a partner’s effective treatment add much more protection.
  • It doesn’t protect the partners of men with HIV. A trial in which men who already had HIV were circumcised found it didn’t reduce HIV transmission to their female partners.
  • It doesn’t directly protect the receptive partner. If you’re the receptive partner, what matters is whether your partner has HIV, not whether he’s circumcised.
  • It doesn’t replace PEP. After a recent exposure, being circumcised is not a reason to skip PEP (post-exposure prophylaxis).

Men who have sex with men

For gay, bisexual and other men who have sex with men, the evidence is less clear. A Cochrane review found that circumcision may protect men who mainly take the insertive role in anal sex. But its overall role in preventing HIV among men who have sex with men is still uncertain. There isn’t enough evidence to recommend it for HIV prevention in this group.

The receptive partner in anal sex faces by far the highest risk, and circumcision doesn’t change that. PrEP, condoms and a partner’s undetectable viral load are the tools that work here. See HIV risk for gay and bisexual men.

Does a circumcised partner lower your risk?

Sometimes, in a different way. In countries where HIV spreads mainly through sex between men and women, circumcised men are less likely to have HIV in the first place, because circumcision protected them. The calculator treats a circumcised male partner of unknown status as about 50% less likely to have HIV than an uncircumcised man, adjusted for how common circumcision is in each country. This adjustment isn’t applied to men who have sex with men.

For a woman in South Africa having vaginal sex once with a man of unknown status, the estimate is 0.0029% (about 1 in 34,000) if he isn’t circumcised and 0.0015% (about 1 in 68,000) if he is.

This only changes the chance that he has HIV. If a circumcised man does have HIV, his circumcision doesn’t make him less likely to pass it on.

What to do now

Had sex without a condom in the last 72 hours with someone who has HIV or whose status you don’t know? Being circumcised doesn’t replace PEP. Ask about PEP now: it must start within 72 hours, ideally within 24. See how to get PEP.

  • Get tested after a possible exposure, at the right time. See HIV test accuracy by week.
  • Use condoms with new partners or partners whose status you don’t know. They lower risk by about 80%.
  • Consider PrEP if you’re often exposed. It protects you whether or not you’re circumcised. Read about PrEP and PEP.
  • Thinking about circumcision for HIV prevention? Talk it through with a doctor. It’s one layer of protection for men who have vaginal sex, not a replacement for the others.