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HealthStudy: 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. (upi.com)

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[–]kerovonGrad Student|Biomedical Engineering|Regenerative Medicine 883ポイント884ポイント  (131子コメント)

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.

[–]homequestion 59ポイント60ポイント  (3子コメント)

And there was no average difference in sensitivity between B and C?

Edit: Actually, I was assuming they tested B and then C (with the foreskin pulled back). Did they not do this?

[–]ThrobAway [スコア非表示]  (0子コメント)

And this is ignoring the most critical part of the issue, which is that there is an enormous difference in the sensitivity of the foreskin. That is, the problem is cutting off the nerves at all, not necessarily how that affects the remainder of the organ - the foreskin contains a large fraction of the sensory neurons in the penis.

[–]wearethat 4ポイント5ポイント  (2子コメント)

screening out people with STDs, sexual dysfunction, cardiovascular condtions, smokers, etc.

Layman question: What % of the population does this kind of criteria include/exclude?

[–]andrewslug [スコア非表示]  (0子コメント)

Hard to say exactly, but at least 30% based on smoking and std rates.

[–]WordSalad11 [スコア非表示]  (0子コメント)

The study should have a consort diagram that spells out exactly how many people were screened and how many were enrolled.

[–]turtley_different [スコア非表示]  (3子コメント)

Thanks. Great summary and definitely needed.

I just want to flag that the results plot does, by visual inspection of plot C, suggest that there is a statistically lower heat detection threshold for the foreskin vs. elsewhere. The authors don't say there is, but it is pretty blatant if those error bars are 1-sigma. The plot is wrong or the text is IMHO.

[–]kerovonGrad Student|Biomedical Engineering|Regenerative Medicine [スコア非表示]  (1子コメント)

They do say that a power analysis indicated that they need a larger sample size (238) for the warmth detection to identify a significant effect within the penis sites. So I do more or less believe that they didn't come up with a significant difference, and it actually says pretty good things about their statistical honesty that they talked about their study being underpowered for that stimuli.

[–]its_switz [スコア非表示]  (0子コメント)

they need a larger sample size (238)

Well that's just shy of 4 times their actual sample size, so yes, that result is far from significant.

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    [–]Discarnated 12ポイント13ポイント  (29子コメント)

    Why weed out smokers?

    [–]trumpetspieler 180ポイント181ポイント  (5子コメント)

    Usually are at risk for poor circulation.

    [–]Mr_Dugan 85ポイント86ポイント  (16子コメント)

    Smoking damages blood vessels. Excluding smokers eliminates a potential confounder

    [–]iObeyTheHivemind 1ポイント2ポイント  (12子コメント)

    Is that the nicotine or the smoking itself?

    [–]Mr_Dugan 9ポイント10ポイント  (3子コメント)

    Sorry, but I don't know. When inhaling cigarettes you get a lot of extra junk with the nicotine. I highly doubt there is enough evidence to say how much just nicotine contributes to atherosclerosis versus the other chemical components in cigarette smoke.

    [–]sfurbo 4ポイント5ポイント  (0子コメント)

    Ncotine by itself can cause some damage (http://www.medicaldaily.com/its-not-smoke-its-nicotine-e-cigarettes-may-damage-arteries-265498). It does not seem to be known if the damage from only nicotine is enough to have a clinically significant effect.

    [–]Augustus_Trollus_III 3ポイント4ポイント  (0子コメント)

    Nicotine is a vasoconstrictor

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        [–]JuanDeLasNieves_ [スコア非表示]  (0子コメント)

        Aside from what people mentioned regarding circulation issues, you want your subjects to be comparable. So either you have all smokers or none at all and since smoking can introduce a new variable in this scenario, it's best to have all non-smokers.

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          [–]Aezay 20ポイント21ポイント  (4子コメント)

          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.

          Perhaps they should have included testing of the frenulum as well, as that is sort of the male equivalent of the clitoris in terms of sensitivity.

          [–]CJGibson 47ポイント48ポイント  (22子コメント)

          What are the chances that people with sensitive penises self-select out of a study to test penis sensitivity? Do they do anything to account for that possibility?

          [–]MotorcycleCK 78ポイント79ポイント  (12子コメント)

          But how would they know that their penis is more sensitive than most others?

          [–]TheSystem_IsDown [スコア非表示]  (1子コメント)

          Out of 32, and with a college-age average, I'm pretty sure it's completely random who self-selected for this test, including those with sensitive glans.

          [–]Trickster_2212 1ポイント2ポイント  (2子コメント)

          How would that make a difference?

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            [–]CaptchaInTheRye [スコア非表示]  (12子コメント)

            Since this is the top comment, I would like to add on to your (very informative) post, and say that even if the study did find that circumcision does not reduce penis sensitivity at all, that is only one very small reason to be against circumcision of babies.

            The #1 reason, above all else by far, is that the penis belongs to the baby, the decision is his to make, he's not old enough to decide, and it's irreversible.

            All the other stuff is just refutation or support of details in each side's case. The above is why it's really wrong.

            [–]Go0s3 [スコア非表示]  (0子コメント)

            Question. Does the scientific community accept results determined from subsets lower than 1000?

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              [–]EntropyNZ 358ポイント359ポイント  (24子コメント)

              I've just had a read through the full article for this, and there's a few massive, glaring holes in their methodology.

              Firstly, the testing sites used. There's the obvious elephant in the room in the 'how do you compare sensation when one of the groups lacks the area that you're testing on". The answer is that they didn't (and obviously couldn't). The testing site on the foreskin was only done on uncircumcised men.

              However, this testing site was also ON THE OUTSIDE OF THE FORESKIN. There was no testing site done on inside of the foreskin (the mucus membrane), which is the sensitive aspect of the foreskin. The outside is just skin (normal epithelial tissue); it's an extension of the skin on of the rest of the penis. That's the same as claiming that cauterizing the inside of someone's nose doesn't alter sensation when you've only tested sites on the outside of the nose. You literally missed the part that you were actually supposed to test.

              The other issue is the testing used to determine sensitivity. For tactile sensation, they used a pressure-thresh-hold test (testing minimum level of pressure able to be perceived) and similar methods for the pain thresh-hold test (which is when the sensation becomes painful, not how much pain they can tolerate). Both of those are fine, but there's others that are just as easy and probably more useful in determining tactile sensitivity. For instance, where's the two point discrimination testing (minimum distance at which you can differentiate two points of pressure from a single point)? That's a much better test of overall sensitivity.

              Temperature testing was OK (point heat increasing at .5 deg C per sec, patient indicates when they are able to notice a change in heat, as well as heat tolerance, which is pretty self explanatory).

              The overall finding were that the foreskin was found to be more sensitive in tactile threshold testing than the rest of the penis, but that their findings showed no other significant differences. They note several times that this is contrary to previous studies.

              For anyone interested, sample size was a total of 62 men (age 18 to 37 years, mean 24.1, SD 5.1), which is pretty standard for this kind of study.

              On the flip side, interesting findings from the study were they they didn't find any significant difference between glans sensitivity between groups, which would be expected from a physiological perspective, as the glans SHOULD keratanise without a foreskin (like every other mucocutaneous tissue in the body does in response to exposing it directly to air and contact to other non-mucocutaneous surfaces for any prolonged period), and SHOULD have a higher threshold for sensory stimulus as a result. Again, this finding is contrary to previous studies, which have found the expected changes to the glans with circumcision.

              Someone needs to do a histology study that looks at epithelial tissue from the glans of circumcised and uncircumcised men to determine the level of keratinisation present. The study above stated that one of their hypothesis was:

              "2) Differences in penile sensitivity between the groups will be most pronounced at the glans penis, where keratinization is hypothesized to take place"

              Now I'm sure that's just poorly worded, because it's well understood that the glans is heavily keratinised in comparison to the other tissues of the penis, and that they meant to say '... the increased/further keratinization...", and that's something that's fairly easy to determine, although it does involve lopping small bits of glans off, which I'm sure you'd struggle to find participants for.

              [–]Orckilla [スコア非表示]  (7子コメント)

              They pulled the foreskin back.

              Edit:they tested a fifth spot on men with foreskin, as a study point. Obviously they cannot compare that to a guy without one.

              [–]DoubleDot7 [スコア非表示]  (0子コメント)

              There was no testing site on inside of the foreskin

              Honest question from someone without any experience with foreskins: Is that really a big issue? If it's on the inside, how much of contact would it really make with other surfaces?

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                [–]DinkyWinkyDoo 92ポイント93ポイント  (55子コメント)

                Anecdotes aside, isn't the argument usually that circumcision removes sensitivity of the foreskin (which makes sense, as foreskin is removed in circumcision)? The study seems a moot point.

                Is it surprising that cutting off one aspect of an organ does not impact on the rest of the organ's sensitivity? We do not associate surgeries or scratches elsewhere on the body to decreased sensitivity either, for example, regardless of location, unless there is severe nerve damage.

                What am I missing here?

                [–]bumpfirestock 24ポイント25ポイント  (5子コメント)

                Correct me if I'm wrong, but anectdotally the hand is a major example of reduced sensitivity due to "wear and tear". The commentor at the top of this post mentioned keratinization, I assume that means some sort of mild scarring or a buildup of a skin later with fewer nerves. The major hypothesis I've heard regarding circumcision is that when the head rubs the inside of someone's boxers, the same thing happens that happens to a farmer's hands when he used a shovel all week - decreased sensitivity. This is way out of my educational expertise (perhaps obviously so), so just speculation. But this study basically states there is no statistical reduction in sensitivity due to not having a foreskin.

                [–]DinkyWinkyDoo [スコア非表示]  (3子コメント)

                Yeah. If we believe the study, then it might be different between the hand and genitals because of a "genetic preconception" if you will- evolution has us have hardening soles of the feet and numbed hands, but we maintain a sensitivity in various spots regardless of torture

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                  [–]greyjackal [スコア非表示]  (2子コメント)

                  circumcision removes sensitivity of the foreskin

                  I thought it was of the glans?

                  [–]DinkyWinkyDoo [スコア非表示]  (1子コメント)

                  Well that's certainly what a lot of people argue, but you surely don't disagree that circumcision removes sensitivity of the foreskin! And that's my point.

                  [–]HoldMyWater 37ポイント38ポイント  (7子コメント)

                  Is it surprising that cutting off one aspect of an organ does not impact on the rest of the organ's sensitivity?

                  Um, yes? Especially given the fact that the foreskin's function is as a protective layer on top of the head of the penis? It's the difference between the head rubbing on the fabric of your underwear 24/7 vs not.

                  In that sense, I think this study is interesting. It doesn't change my opinion on the matter of whether it should be allowed (on babies), but it's still interesting.

                  [–]DinkyWinkyDoo 5ポイント6ポイント  (5子コメント)

                  I'm not at expert in the field of this particular genital and I certainly won't claim to be, and I'm not ruling in either favour when I write my comment above accordingly. I understand your reasoning from a LOGICAL perspective, but from a statistical perspective with hard facts I can totally believe that sensitivity does not meaningfully change. "It's a sensitive area regardless" sort of thing.

                  I wonder, could anyone in this thread provide information on what happens to the inner membrane of the nose if it is exposed? Does it become desensitised, or does it stay sensitive regardless, in the same way that this study announces for a different area?

                  [–]HoldMyWater 2ポイント3ポイント  (1子コメント)

                  but from a statistical perspective with hard facts I can totally believe that sensitivity does not meaningfully change.

                  You asked if the result was surprising... not what the results were. Given the results now, it's no longer surprising. Yes, I agree...

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                      [–]marcm6246 7ポイント8ポイント  (5子コメント)

                      The biggest reasoning behind it was that there's several special nerve endings in the foreskin that are absent in just regular skin. It was presumed that removing these nerve endings = removing specific sensations that would lead to sexual pleasure.

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                        [–]thedstrat 123ポイント124ポイント  (32子コメント)

                        The article directly contradicts the title; there were differences in tactile feeling. "In men with foreskin, it was more sensitive to tactile stimulation than other parts of their penises".

                        [–]Null_Mutant_Tortoise 63ポイント64ポイント  (9子コメント)

                        We found that while the foreskin was more sensitive to fine touch, it was not more sensitive to the other stimuli we used, and those stimuli are likely more important in sexual pleasure.

                        Not directly contradicting what you said, but it's an important clarification.

                        [–]Blackdutchie 19ポイント20ポイント  (8子コメント)

                        Do they have any sources for their claim that Heat, heat pain, and pain are more important in sexual pleasure than fine touch?

                        I'd accept if they made a case for (and measured) frictional sensitivity, but this does not seem to be the case from what I can access.

                        [–]Null_Mutant_Tortoise 9ポイント10ポイント  (3子コメント)

                        I'm just saying that that's what they believe. And they probably know much more about penis stimulation than I do. Whether there is hard evidence, I don't know.

                        [–]tripletstate [スコア非表示]  (0子コメント)

                        Since when is heat and pain part of sex? Well, not part of my sex.

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                          [–]kerovonGrad Student|Biomedical Engineering|Regenerative Medicine 140ポイント141ポイント  (20子コメント)

                          That is finding that the foreskin of uncircumcized men was more sensitive than the rest of their penis. It is not contradicting the title.

                          [–]Blackdutchie 54ポイント55ポイント  (15子コメント)

                          Direct Quote from abstract:

                          Penile sensitivity did not differ across circumcision status for any stimulus type or penile site. The foreskin of intact men was more sensitive to tactile stimulation than the other penile sites, but this finding did not extend to any other stimuli (where foreskin sensitivity was comparable to the other sites tested).

                          Emphasis mine.

                          So in tactile stimulation, the foreskin is the most sensitive part of the penis (when it occurs)

                          The foreskin is generally considered part of the penis.

                          Therefore, TOTAL sensitivity of the penis is higher in men with foreskin than men without, HOWEVER, there is no measurable difference in the other parts of the penis.

                          [–]mugdays 63ポイント64ポイント  (14子コメント)

                          Therefore, TOTAL sensitivity of the penis is higher in men with foreskin than men without, HOWEVER, there is no measurable difference in the other parts of the penis.

                          Isn't that really obvious? Men with foreskin have more foreskin sensitivity than men without foreskin.

                          [–]Krakkin 26ポイント27ポイント  (4子コメント)

                          You would think so.

                          [–]Conisewer 20ポイント21ポイント  (3子コメント)

                          You would think so, however that point seems to be ignored in many parts of this thread. No one wants to believe that they are missing out on a significant amount of tactile stimulation on the very best place to be tactiley stimulated.

                          [–]BraveLittleCatapultBS|Biomedical Engineering and Design [スコア非表示]  (0子コメント)

                          This subject is A) subjective and anecdotal at its core B) beaten to death on this site. No one with a foreskin knows how much relative stimulation he is recieving compared to someone who is circumcised and vice versa. I would argue that objectively measuring sensitivity is damned near impossible due to the more systemic features of the nervous system, such as variant receptor density. We are all "tuned" so differently when it comes to tactile sensation and nociception. A slap on the wrist may feel like a slap on the wrist to you, but a punch on the wrist to someone else. I know these studies use threshold values to represent sensitivity, but think about that. Does that really encompass tactile sensation?

                          [–]CRAZYSCIENTIST 4ポイント5ポイント  (0子コメント)

                          They have more foreskin sensitivity (obviously) AND the foreskin is the most sensitive part of their penis.

                          [–]my-inbox-is-open 2ポイント3ポイント  (0子コメント)

                          The point being made is that the foreskin of men who are intact is more sensitive (when using tactile stimulation) than any other area of the circumcised penis

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                            [–]Salindurthas 44ポイント45ポイント  (2子コメント)

                            Doesn't it?

                            • The foreskin was more sensitive than the rest of the penis.

                            • The non-foerskin parts of the penis were equally sensitive in both groups (rather, no difference was found) correct?

                            • So clearly the uncircumcised penises were more sensitivity, since they had a region of higher sensitivity (and the rest being supposedly equal).

                            Or did I misunderstand something?

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                              [–]turtley_different 14ポイント15ポイント  (2子コメント)

                              The title for this reddit post is, at best, missing important data from the study; at worst it is actively obfuscating the findings of the study. I think that is irresponsible for a front-page post.

                              As per /u/kerovon 's ongoing post, the results plot shows the foreskin has (a statistically significantly) lower threshold sensation for touch and heat**.

                              Of course, whether tactile and heat sensitivity correspond to sexual pleasure in any meaningful sense is a different question and not one that the study addresses (but seems to be pretty heavy subtext for the reddit interest).

                              ** the text below the diagram doesn't state this for heat, but foreskin heat sensitivity is multiple sigma removed from other sites. I would say the result is in fact stronger than the tactile one -- looks like a rather fundamental error in the paper. I welcome correction if I'm wrong.

                              [–]Gravybone 10ポイント11ポイント  (4子コメント)

                              When we think about the way the human nervous system (and that of most vertebrates) interfaces with the brain this makes a lot of sense:

                              Tactile sensations are mapped to the brain in a way that's referred to as a cortical homunculus. Certain sections of the surface area of the cerebral cortex corresponds to various parts of the body, and their surface area is directly proportional to amount of sensation in a given area.

                              Therefore, though I am not an expert on the specifics of this subject by any means so I could be off base here, the amount of sensation in the penis should be directly tied to an amount of surface area in the brain, and not an amount of nerve endings in the penis. Even a small amount of nerve endings can be mapped to a large region of the brain, and when nerve endings are lost, areas of the brain are remapped to existing nerve endings. Brain damage and stroke can lead to changes in the cortical homonculus, but physical damage to the nervous system does not, except to free up brain surface area which will likely be remapped to nearby nerves.

                              Edit: words

                              [–]MaVagina [スコア非表示]  (0子コメント)

                              Their next study needs to compare the differences in penile sensitivity in circumcised and uncircumcised males, vs the circumcised and uncircumcised males' emotional sensitivity regarding the shape of their penises.

                              [–]hirsutesuit 10ポイント11ポイント  (1子コメント)

                              The foreskin of intact men was more sensitive to tactile stimulation than the other penile sites.

                              Is tactile stimulation not the type of stimulation that anyone concerned about circumcision would care about?

                              [–]BewBewKittyFuck [スコア非表示]  (13子コメント)

                              I love how everyone is finding fault with this study simply because they don't agree with the findings.

                              Go collect your own empirical evidence and then get back to us.

                              [–]Legendhidde [スコア非表示]  (10子コメント)

                              Funny how you dismiss scientific criticism because you don't agree with the stance it takes, while providing no arguments to counter them. Nope, just whining is enough.

                              [–]HaberdasherA [スコア非表示]  (2子コメント)

                              This isn't legitimate peer reviewed criticism though, this is just a bunch of random people on reddit getting emotional because they don't like circumcision.

                              [–]Neglectful_Stranger [スコア非表示]  (3子コメント)

                              Look at the amount of deleted posts in this thread and try to tell me that people aren't arguing against it with something other than anecdotal evidence.

                              [–]orge [スコア非表示]  (0子コメント)

                              Science is about objectivity, lets try not to get emotional.

                              [–]gokucanbeatsuperman [スコア非表示]  (0子コメント)

                              That's exactly what a lot of people are doing. They have no problem claiming studies to be the absolute truth but as soon as they disagree with it because it doesnt fit with their world view they just as easily dismiss it.

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                                  [–]hirsutesuit 1ポイント2ポイント  (1子コメント)

                                  They did these tests at 3-4 penile sites and found no difference in sensitivity. As the full text is behind a paywall can anyone tell me if they address the removal of the foreskin and how it would influence the "quantity" of sensation? It seems evident that removing a portion of sensitive tissue would make the total less sensitive.

                                  [–]allacctsarethrowaway 3ポイント4ポイント  (0子コメント)

                                  It would also seem evident that amputating a painful extremity would make that extremity hurt less, but this is not always the case.

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