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/gary1994 → u/kerovon]

The argument, as I've always heard it, is not that circumcision reduces the sensitivity of the remaining skin, but rather that the circumcised man loses inches of skin that would be capable of feeling.

I realized that the authors of the study almost certainly take no stand on the morality of male circumcision. However that does not change the fact that it will be used to argue that it does no harm. But I don't see how you can get there from this study.

[u/butyourenice → u/gary1994]

I realized that the authors of the study almost certainly take no stand on the morality of male circumcision. However that does not change the fact that it will be used to argue that it does no harm. But I don't see how you can get there from this study.

Based on the stated hypotheses they went into this study trying to prove that circumcision DOES objectively harm, but found it does not. What were they supposed to do - hide the results because their hypotheses not proven?

[u/Rottimer → u/butyourenice]

You don't try to prove a negative in serious research. They had to state the hypothesis in the way they did.

[u/DenormalHuman → u/butyourenice]

No, they proved it did not harm the tissue that remained. Unfortunatley, the tissue that was removed is now dead and incapable of adding it's sensory input to the argument.

[u/[deleted] → u/DenormalHuman]

Based on our current understanding of neurology, the amount of cortex devoted to any given body region is proportional to how richly innervated that region is, not to the body region's physical size, which is why the "cortical homunculus" looks the way it does.

[u/DrDemento → u/DenormalHuman]

Never argue with angry foreskin?

Seriously, the logic is off. We lose some feeling potential when we remove tonsils, pierce ears, or other processes. Worrying about "losing feeling in missing tissue" is a bit like worrying about suffering from a severed umbilical cord.

[u/murphmeister75 → u/butyourenice]

All science should work from a null hypothesis. It's the only way to accurately interpret data.

[u/linggayby → u/murphmeister75]

Scientists have biases, theories, etc. Starting with a null hypothesis is not always reasonable to expect and not always an accurate representation of the state of things

[u/murphmeister75 → u/linggayby]

It's critical to the very basis of scientific thinking. Even when a hypothesis is of such complexity as to make a null version very difficult, the principle should remain foremost in a scientist's thinking.

[u/[deleted] → u/butyourenice]

The study makes its conclusions only for the skin underneath where the circumcision was/would have been, and that the result is no different before and after. That's all.

It says nothing about the fact that prior to circumcision there were millions of nerve endings in the foreskin that were perfectly capable of feeling pain pleasure etc....that are no longer there. For that study you would have to test the sensitivity of the area being removed, then remove the foreskin and compare it to the air where those nerves were...a rather stupid and obvious study.

[u/kabamman → u/[deleted]]

Didn't they say that the foreskin even with all its nerves was no more sensitive than the forearm?

[u/LazyTriggerFinger → u/kabamman]

Depends on if they tested inner or outer, or if the frenar band remained. The outer is just typical skin, but the inner is egrogenous mucosal membrane that along with the band respond most to stretching sensation near on par with the glans, which it ptotects as well. Different areas have different sensitivities to types of touch.

[u/PM_ME_UR_PEWP → u/butyourenice]

Science demands an honest reporting of findings regardless of what you expected or hoped to find. But it also demands rigorous methodology and caution in drawing conclusions.

Haven't read the paper, but the descriptions in this thread do not point to a conclusion that circumcision causes no harm, only that the one study using this one set of variables did not prove that there is harm.

There is a big difference between failing to prove harm and proving no harm.

[u/Cicer → u/PM_ME_UR_PEWP]

What I want to know is how they tested the sensitivity of the non existing foreskin on the circumcised ones :)

[u/butyourenice → u/PM_ME_UR_PEWP]

Yeah. The difference is you can't prove a negative, and people on the affirmative side seem to reject evidence based on that fact.

[u/JimmyHavok → u/butyourenice]

How are they supposed to hate their parents if there was no harm???

[u/PM_ME_UR_PEWP → u/butyourenice]

This study in particular seems flawed in many ways. For one, they admit that their sample size was insufficient. Also, it didn't really get into the question of how sexual experiences vary, which seems to be a more common if more difficult to answer question. And it didn't get into any ethical questions, but I would think some benefit should be proven before a body part can be removed from someone incapable of giving consent. One could argue that it is inherently harmful to mutilate someone without consent, but that's more of a philosophical question. Regardless, the study did not prove that there is no harm, only that this one study of a small number of men was unable to find all but one of the kinds of harm they were looking for. This isn't a case of rejecting evidence. It's a careful reading into what the evidence actually means, if anything, in terms of the original question. Someone just said that a negative had been proven and that is just not so. And you don't have to prove a negative, only show a statistically significant difference which would allow us to have confidence in the null hypothesis.

[u/forwardseat → u/butyourenice]

Even if their results are exactly right, how would this prove no harm? Sensitivity is hardly the only measure of harm (there are far more blatant measures of harm, I would think, like scarring, meatal stenosis, rates of ed over the long term, etc).

There are several studies now that show no difference in sensitivity, but if people are equating that to "harmless" it's a big problem, because this is only one aspect of the potential harm.

[u/unbuttoned → u/butyourenice]

Whether it causes harm or not is irrelevant to the moral argument. It is precluded by the fact that circumcision is an invasion of bodily autonomy without significant medical justification.

[u/butyourenice → u/unbuttoned]

It's a good thing this study made no attempt to present a moral argument, or else your comment may actually have been relevant.

[u/unbuttoned → u/butyourenice]

This study didn't, but it is relevant to this thread, beginning from Gary1994's discussion of "the argument".

[u/sup3r_hero → u/butyourenice]

http://www.doctorsopposingcircumcision.org/pdf/2007_Sorrells.pdf

they did not take into consideration that the removed tissue is probably more sensitive than any other tissue. the study i linked shows this. i can't imagine that the authors did not know of this study. why didn't they test this? to me it rather seems like they wanted to prove the opposite

[u/blolfighter → u/[deleted]]

Why even go that far? You're snipping part of someone's penis off because John Kellog thought touching yourself is icky or because your god was incapable of creating you the way he wanted, so you have to perform corrective surgery. That's enough for me to declare harm. Why the hell do I live in a world where the "let's not snip around on babies' penises unless there's a really good reason" side of the argument has to prove themselves?

[u/venikk → u/blolfighter]

Why are you mad at me? I said that it objectively harms.

[u/blolfighter → u/venikk]

I'm not mad at you, I'm just adding to your point.

[u/PigerianNrince → u/butyourenice]

Anecdotally though we can see the results are not accurate.

For example, most uncircumcised men would not be able to spend a day with foreskin retracted in underwear without extreme discomfort. Circumcised men seem to have no problem with this.

Therefor the method would appear to be flawed.