For some, circumcision is a religious or cultural act. For others, it's a health decision. Yet even among medical experts, not everyone agrees on whether removing the foreskin of a male person has any real clinical benefits.

A small new study involving 11 children in the United States has found evidence that removing the skin that covers the tip of the penis can change the abundance and composition of bacterial and fungal communities that naturally live there.

But what would that actually mean in practice?

Some of the bacterial communities that shrank following circumcision have been linked to inflammation and sexually transmitted infections (STIs) in other research. That tentatively implies circumcision may reduce a person's susceptibility to STIs by limiting inflammation in penile tissues and viral targets on the skin.

The microbiome is a new frontier in scientific research, and while we're getting a better idea of how microbes that occupy our bodies can impact our health, the penile microbiome is not nearly as well-studied as, say, the gut, or even the vaginal microbiome.

To date, there is limited data and a lack of controlled studies on circumcision from which to draw any conclusions. Especially when you consider past studies with null results, which tend to get overlooked.

So let's dig in to the literature.

The theory that circumcision protects against STIs has been in circulation since at least the 1800s, when a scientist by the name of Jonathan Hutchinson posited circumcised Jewish people in London were more protected against syphilis than uncircumcised communities.

Other scientists of the time, however, argued Hutchinson was jumping to conclusions. Correlation, they warned, does not equal causation. There could be other confounding factors influencing this statistical link.

Today, that very same debate is still in full swing, and both sides think they are being more scientific and evidence-based than the other.

Dozens of observational studies and a few randomized clinical trials over the years have found evidence that suggests circumcision can protect individuals from some STIs, at least to some extent.

Meta-analyses based on global data, for instance, have found circumcision is linked to a reduction in bacterial infections, like syphilis, or viral infections, like genital herpes, or herpes simplex virus type 2.

In 2020, two studies found evidence that circumcised adults have a different penile microbiome to those who are uncircumcised, and this was shown to somewhat protect the former group from spreading bacterial vaginosis or contracting human immunodeficiency virus ( HIV/ AIDS).

The results around HIV are particularly contentious.

Based on observational data collected in South Africa, researchers have argued circumcision could be more effective for HIV transmission among heterosexuals "equivalent to what a vaccine of high efficacy would have achieved" (if one existed).

Such conclusions are based on results from three large, randomized controlled trials conducted in Africa among adult males that showed circumcision might lower the risk of contracting HIV by 50 to 60 percent.

While that sounds incredible (and, some counter, clearly overstated), other studies challenge notions of a relationship between HIV infection and circumcision. In October of 2022, a study again examined the statistics behind male circumcision and HIV prevalence among six African nations, but no link was found.

"The study questions the current strategy of large scale Voluntary Medical Male Circumcision (VMMC) campaigns to control the HIV epidemic. These campaigns also raise a number of ethical issues," the authors of that study argue.

In Africa, circumcision is extremely common and widespread. While cases are largely for cultural reasons, there has also been a push to introduce the practice as a way to stem the spread of HIV.

In the year 2000, scientists proposed that circumcision protected against inflammation and HIV infection by changing the penile microbiome.

The recent study on 11 children is the first of its kind to show microbiome changes can follow circumcision. As intriguing as the results are, the small sample size and the fact it doesn't prove a causal effect are reason enough to remain somewhat skeptical.

Of course, it might be true that removing the foreskin changes a penis's microbiome. But how those changes impact infection is still unclear. Some changes might be good for health. Others might harm it.

In Denmark, for instance, a population-based study that spanned three decades found no evidence that circumcision in infancy or childhood protected against HIV or other STIs. In fact, in this particular study, circumcision was actually linked to higher STI rates overall, especially for genital warts and syphilis.

Many of the studies on circumcision to date have been conducted among heterosexual adult males in developing nations. Whether those results translate to other parts of the world or to gay or queer individuals remains unclear. There are numerous factors that influence human health and many more that control bacterial and viral spread.

Nevertheless, in 2007, the US American Academy of Pediatrics reviewed the literature on circumcision and argued the "current evidence indicates that the health benefits of newborn male circumcision outweigh the risks."

In comparison, officials at the US Centers for Disease Control and Prevention acknowledge that circumcision may partially protect from HIV, but at the same time, they argue there is not rigorous evidence to suggest male circumcision can reduce HIV transmission among the gay and queer community.

Without more robust clinical studies on circumcision, the penis' microbiome, and sexually transmitted infections, the evidence will remain deeply conflicting for parents and experts alike.

The study was published in European Urology Focus.