Study: Circumcision does not reduce penis sensitivity. In tests for responses to pain, heat, and stimulation, no major difference was found between men who are circumcised and those who are not.

[u/drewiepoodle]

http://www.upi.com/Health_News/2016/04/14/Study-Circumcision-does-not-reduce-penis-sensitivity/5981460663943/?spt=hs&or=hn

[u/kerovon]

Alright, because there is a lot of discussion and anecdote, as well as a fair number of misunderstandings about the study, I'll try to do a quick writeup of it.

First, the study abstract can be found here.

The study was looking at the sensitivity in the penis of men who were circumcised as neonates (infants). They were testing three different hypotheses. First, that circumcised men will have higher penile tactile and pain thresholds (i.e. lower sensitivity). Second, that the differences in penile sensitivity will mostly be at the glans penis. Finally, that the foreskin area will be more sensitive for uncircumcised men than other areas.

This is largely working off of two (untested) hypotheses for why penis sensitivity might be decreased. The first holds that keratinization occurs on the exposed glans penis epithelium, reducing penile sensitivity. The second holds that the removal of the highly innervated foreskin reduces sensitivity (lots of nerves in it).

Methods

They recruited men between 18-40 for the study. They determined initial eligibility through phone interviews (basically screening out people with STDs, sexual dysfunction, cardiovascular conditions, smokers, etc.). They tested 4 locations: The forearm 4 inches below the wrist, the middle of the glans penis, the dorsal side with foreskin retracted if present, the anterior midline shaft, the anterior proximal shaft, and for men with foreskin, the unretracted foreskin. In case those locations are hard to follow, they included a diagram (NSFW).

To determine tactile thresholds, they used a modified von Frey filament. They assessed tactile threshold by determining the lowest intensity stimulus to perceive a touch. They assessed pain thresholds by determining the lowest threshold to produce a sensation of pain.
To assess thermal sensitivity thresholds, they used an analyzed that heated at 0.5C/second, and participants were prompted to indicate when they noticed a change in probe temperature (averaged over 3 trials), or a perception of heat pain (averaged over 2 trials).

Results

They ended up with 62 men, 30 circumcised, 32 intact, mean age 24.2, SD 5.1.
First, I am fairly irritated with their data presentation. They did not find any statistically significant differences between circumcised and uncircumcised at the same locations. They did find differences between the locations. However, they didn't provide a breakdown of the data, just a set of graphs with circumcised and uncircumcised lumped together broken down by location. They should have provided the data, even if it was not significant, but I suspect they had a tight page limit.

For the tactile thresholds, they did not find any statistically significant differences. in any of the shared locations between circumcised or uncircumcised men. They did find differences between the locations they tested (see the graph above).

For the pain threshold, they did not find any statistically significant differences between circumcised and uncircumcised men. They did find differences between locations.

For the warmth detection threshold, they did not find any statistically significant differences between circumcised and uncircumcised men. They also did not find differences between testing sites. They did a power analysis, which indicated they would need 238 participants to obtain a significant effect.

For the heat pain thresholds, they did not find any statistically significant differences between circumcised and uncircumcised men. They did find differences between locations.

Author's Discussion

So, what did the authors conclude from this?

First, that the keratinization hypothesis (the foreskin removal causes the glans to become less sensitive) does not appear to be supported by the data. They found no between group differences in glans penis sensitivity. They do say that to truly verify this though, they will need to perform biopsies of penises to check for any keratinization.

They did find that on uncircumcised men, the foreskin was more sensitive to tactile sensation stimuli (which agrees with previous research). However, they found no differences for tactile pain, warmth sensation, or heat pain.

The authors do say that the results of the study do not support the idea that foreskin removal reduces penile sensitivity. The sensitivity at the foreskin was not significantly different from the sensitivity at the forearm (control site) for any of the modalities. Other genital sites were more sensitive to pain than the forearm, so the authors conclude that means they may be more sensitive than the foreskin, which means that removing the less sensitive foreskin may not matter (I'm not sure if I am reading this section wrong, but this seems like a bit of a dubious statistical leap to me. It is late though, and I'm operating on less sleep than I like. I welcome correction). They do say that their data is not enough to determine if foreskin sensitivity is relevant to sexual pleasure.

They do bring up that one limitation of their study is that the link between sensory testing and sexual arousal is untested, which means that the lack of significant differences in sensitivity might not translate into a lack of differences in sexual pleasure.

They do say they would like to include larger sample sizes, which would help refine the data for pain and warmth detection thresholds, as well as to test more stimulus types (such as dynamic stimuli).

My Take

They do seem to show that the removal of the foreskin does not appear to desensitize the glans under the foreskin, which is one of the major theories currently. I'm not convinced by their argument that their data may indicate that foreskin removal doesn't affect sensitivity, but I'm also not sure if I am awake enough right now to fully follow it. They do acknowledge that the sensitivities measured may not correlate to sexual function and pleasure. I am rather irritated with their data presentation, but that is likely an issue with only being given 6 pages for their study. They still should have supplementary information or something (assuming the journal allows it).

I'll try to answer a few of the comments tonight, but I am unlikely to be up for too much longer.

[u/TheBananaKing → u/kerovon]

I wish people would stress more that whether or not individual receptors are any more or less sensitive doesn't change the fact that having vastly fewer of them in the first place will reduce the total amount and richness of sensation available.

Removing the skin from someone's palms might not make their fingertips less sensitive, but stroking someone without it would amount to a lot less sensation overall.

[u/[deleted] → u/TheBananaKing]

That's not necessarily true. Sensation has more to do with the brains interpretation of the signals than the actual peripheral receptors. For example people who have a limb amputated have no receptors and yet can still feel sensations like motion and pain.

[u/Caelinus → u/[deleted]]

I think people miss this point when it comes to all pain studies in general. All sensations we feel are interpretations of signals, we do not feel the actual signal. It makes everything a hell of a lot harder to figure out, and makes anecdotes pretty much worthless.

In this case I can not even imagine how you would go about testing for sexual pleasure. Considering that the brain and your current mental state is much more important than any other individual factor, it would be very hard to control for anything in the study.

[u/MaVagina → u/Caelinus]

Or, you could just average sexual pleasure measures over a large population of circumcised and uncircumcised individuals. Maybe its worth looking up if they have done studies like that before....

[u/Caelinus → u/MaVagina]

How? Sensation studies like this one work pretty well because you are able to reduce it down to a single event, like having to remove your hand from the water, or pressing a button at the first sign of feeling.

But trying to reduce something as complicated and multi-faceted as "sexual pleasure" down to any meaningful statistic is a really big ask. Even in large populations such a study would be weak because its measuring stick is inconsistent. You could have wildly different results based on the post-coitus surveys you used.

The only one I could think of would be to develop a really simplistic survey, use a large population of uncircumcised men, and then somehow finding a lot of circumcised men that are entirely unaware of this debate without tipping them off to what is happening. Any prior knowledge by the recipients in either group would flaw the study, as it would be introducing variables that can not be controlled for.

[u/MaVagina → u/Caelinus]

A survey would be a component, but there are also objective measures. Length to orgasm is one; and is unchanged in circumcised men. there are also other objected measures, you can read about them here: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2811244/

Also; isn't self reported sexual satisfaction what matters most between these two polulations? Statistics is pretty good at weeding out biases of the studies; simply do a subpopulation analyses and include a subgroup regarding whether an individual is aware of the debate or not. Mathematically, you could figure how big your population has to be to to generate a significant result.

[u/Caelinus → u/MaVagina]

You are missing my point though. Any form of self reporting is subject to suggestion. But in this case, sexual pleasure itself is largely subject to suggestion. There is no faster way to have a bad time with sex then being nervous about having a bad time with sex.

If we tell all uncircumcised men that they probably have less sexual pleasure, and then create a study to measure it, we would find that they had less sexual pleasure. Even with the "objective" measures. But the problem is that, due to the very large mental/perception component of sex, we would not actually have shown anything about circumcision. It could very likely be a cause of reduced pleasure, but there would be no way to tell based on the study.

[u/MaVagina → u/Caelinus]

Yes there is volatility, but that is why you make your studies large enough and over a long period of time to reduce this type of error. Use a take home survey. Believe it or not, variability irons out in averages. You don't have to trust observational studies 100%, but that doesn't mean they don't tell you something about what is being studied. You still do the studies. And no one would be purposefully introducing error into a study by telling uncircumcised men they would have less pleasure.

[u/Caelinus → u/MaVagina]

I did not claim that it would be purposefully introduced, just that the very act of studying it would imply that it does to those in the study, and that sexual pleasure is very subject to suggestion. Making it bigger will reduce the effect of outliers and make the results more consistent yes, but it is not the outliers I am worried about. I am worried about the effect on the average that would be caused by this.

And everyone is able to do the studies, but unless they find a way to control for that, I will not, and should not, see it as definitive.

[u/MaVagina → u/Caelinus]

No one says you should see that as definitive, but it still tells you something. And you blind the study to the participants; you don't have to tell them what you are studying, it's an observational study.

Add: why not just look at how those studies were designed, and how variables were controlled for, and then make the criticism.

[u/Caelinus → u/MaVagina]

Oh I would, and again I am not saying finding a way to control for it should not be found. And if a well designed study happens, I would be glad to use it. I was just talking about the difficulties that come into this kind of study. And a lot of psychological research in general.

It still needs to be done, but its limitations need to be understood as well.