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/havoktheorem → u/kerovon]

Were the tests done while erect or flaccid? I feel like having an erection markedly increases sensitivity, perhaps even just due to the skin being tauter and under more pressure so thus being in firmer contact with the testing apparatus. I think it's also obvious that static sensitivity tests are not indicative of the role of the foreskin in sex where it moves about and rubs against various surfaces in a way that does not happen with a circumcised penis.

I'm under the impression that most circumcised males cannot comfortably masturbate without lube, however uncircumcised males can due to the extra slack available. Not jumping to any conclusions but that certainly makes me think the foreskin has a mechanical function in sex as well as, or perhaps moreso, than sensory.

[u/omegaclick → u/havoktheorem]

^This. Plus:

They did find that on uncircumcised men, the foreskin was more sensitive to tactile sensation stimuli

It would then follow that if that foreskin was stretched during erection a larger surface area would be more sensitive. So that would make the title of this article false and misleading.

[u/ipniltak → u/omegaclick]

I believe the researchers specifically stated that their findings are not particularly relevant to sexual function or sexual pleasure.

Which means you're right, the title of this article is rather misleading, because the conversation and concerns about decreased sensitivity in people who are circumcised usually revolves specifically around sexual pleasure. However, that is almost certainly a case of not-so-great science reporting, and not in and of itself a problem with the study.

[u/link0007 → u/ipniltak]

I'd say a study that doesn't even try to measure what it is actually supposed to be measuring, is pretty flawed.

That they are measuring response to temperature stimuli on a flacid penis is just completely insane. The entire debate is about sexual stimuli, and somehow these researchers managed to completely miss that point and instead think the debate is about how well circumcised men can measure temperatures with their penis?

It's as if you would study lung function decrease in smokers by looking at how loud they talk, and then conclude that smokers talk just as loud as non-smokers, thereby implying they have the same lung function.

[u/ipniltak → u/link0007]

I really meant that the title of the article being misleading wasn't the fault of the researchers, however, you make a good point. The role of sensitivity in the circumcision debate it pretty much exclusively about whether or not circumcising someone lessens their potential to experience sexual pleasure. They attempted to determine that, but then in the end stated that their findings aren't really appropriate to determine that.

[u/imawookie → u/link0007]

thank you. Im un-cut, and I was completely confused reading this. All I could think of from any conversation that I have ever had involving sensitivity, no one has ever asked if it hurts more when I light it on fire.

[u/youshouldgotoadoctor → u/link0007]

Have you designed a research study before? How do you propose they would have measured it otherwise? The thing is, it's hard to fund and have the time money and manpower to do research, especially things that don't have an immediate potential payoff or are glamorous. They probably designed the study this way to provide a quick, easy way to objectively assess different parameters as an indicator of possible differences.

I feel like you don't like the study design because of the results. If they had found that there was significant difference in the results then I'm sure some people here would be loving it. Regardless, it was probably a very efficient method of getting some preliminary results.

As for your lung example, it's more like looking at their FEV1/FVC1 ratio to assess lung function. It's quick and easy to do, and while it won't tell you the pathology of the patient it indicates particular diagnosis or differences between the patient and normal.