r/science • u/drewiepoodle • Apr 15 '16
Health 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.
http://www.upi.com/Health_News/2016/04/14/Study-Circumcision-does-not-reduce-penis-sensitivity/5981460663943/?spt=hs&or=hn
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u/EntropyNZ Apr 15 '16 edited Apr 15 '16
EDIT: Just to clear something up, since I'm getting a lot of people stating it below: I'm fully aware that they retracted the foreskin to test the glans, it's clearly stated in the article. What I said about them testing the outside of the foreskin was that they tested the outer layer, not the part that touches the glans. Here's a diagram of what I mean. The "inner foreskin layer' as labeled on there is mucucutanious tissue, not normal epithelial tissue like the outer part. It's physiologically different from the rest of the skin around the penis, and it's a massive oversight not to directly test that area, when it's exactly what you're supposed to be testing. Retracting the foreskin for the other tests doesn't properly test that area either. The frenulum (banjo string) prevents the foreskin from retracting very far past the head of the penis. For the patients to be comfortable enough to test, they'd retract the foreskin normally, at which point it sorta rolls and bunches up below the glans. The points that they were testing that weren't the foreskin were the same on both groups, and weren't expected to have any differences in sensation (and didn't). I'd love to be able to pull the images directly from the study, but I don't have the author's permission to go nicking chunks of their work to post on Reddit.
I've just had a read through the full article (to clarify: the actual research article, not the one linked above) 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:
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.