The present study shows that uncircumcised men experience mild to very strong sexual pleasure from the foreskin when stimulated by themselves or partners. They reported that stimulation of their foreskin also generates a moderate to strong orgasm intensity, and very few reported discomfort or numbness of the preputium.

Masters and Johnson 21 compared sensitivity of the ventral and dorsal surfaces of the penis. They found no difference in penile or glans sensitivity between circumcised and uncircumcised men. However, the sensitivity of the preputium was not evaluated. The tendency of Masters and Johnson to support the practice of circumcision and to ignore the sensory function of the preputium may have biased their results. Sorrels et al. 23 included sensitivity of the foreskin in their assessment and found a clear link between tactile penile sensitivity and sexual pleasure. They stressed the importance of the preputium as the most erogenous part of the male sexual anatomy.

Bleustein et al. 27 evaluated glans sensitivity using the Erectile Function Domain of the self‐report questionnaire, International Index of Erectile Function (IIEF), as well as somatosensory testing to compare 62 uncircumcised and 63 neonatally circumcised men. Quantitative somatosensory testing (including vibration, pressure, spatial perception, and warm and cold thermal thresholds) was used on the dorsal midline glans of the penis. After standardisation of the variables no significant somatosensory differences were found. However, decreased orgasm intensity was reported in the circumcised group at the dorsal side of the glans. The somatosensory tests were done on the dorsal midline of the glans with the foreskin retracted in uncircumcised men. By this method the sexual sensitivity of the foreskin and the ridged band were ignored. Disregard of possibly confounding variables and the lack of randomisation to treatment may have biased the results.

The decreased erotic sensitivity after removal of the foreskin is self‐evident. However, the decrease in glans erotic sensitivity is more difficult to understand. It is thought that after circumcision the mucosa of the glans is constantly exposed to friction and irritation. This constant stress provides long‐term keratinisation of the mucosa, making it thicker and dryer. Furthermore, sensitive nerve endings get covered by the thicker mucosal layer and become less sensitive 24 . This concept of keratinisation of the glans is still controversial. In a small population study by Szabo et al. 25 , no increased keratinisation of the glans was found in circumcised men. Another reason for differential sensory changes after circumcision might be a ‘pruning effect’, with arborisation or new branching of nerves that have been severed causing a shift in the dermatome 26 . It may also be that covering of the glans with foreskin prevents direct sensory stimulation in the flaccid state; direct stimulation in the erect, uncovered state then becomes more novel, and thus more sensitive.

The circumcised men indicated lower orgasm intensity at the dorsal and lateral sides of the glans and needed a stronger effort to obtain orgasm than those who were uncircumcised. In addition, a significantly larger percentage of circumcised men reported numbness and unusual sensations at the glans. The most plausible explanation for all the differences listed here is the absence of the foreskin. The removal of the highly innervated foreskin might diminish strong somatosensory sensation, particularly located in the ridge band.

Circumcised men (Group B) showed a significantly lower level of sexual pleasure sensation of the glans. Compared with the strong significant group differences at the dorsal site of the glans, the difference at the ventral side was smaller. This can probably be explained by the presence of the frenulum, which is preserved with circumcision. Sorrels et al. 23 confirmed the high‐density nerve content of the frenulum, when they conducted a Semmes‐Weinstein monofilament test comparing circumcised and uncircumcised men. A significant lower mean was found for the glans vibration threshold in the circumcised men. In both groups the most sensitive area was the frenulum.

The present study showed a marked increase in the percentage of circumcised men who reported pain sensations at the penile shaft. Such pain can be due to traction of the penile shaft skin, or of the area of the circumcision scar, during erection, masturbation and intercourse, and would probably correlate with the extent of the circumcision 28 - 30 . Besides protecting the glans, the foreskin facilitates penetration and sexual stimulation during intercourse and masturbation. Circumcision eliminates this ‘gliding’ mechanism, thereby causing discomfort and pain during self‐stimulation or penetration. Depending on the extent of skin removed, the skin of the penile shaft becomes tenser and loses its flexibility. A significantly higher percentage of circumcised men in the present study reported discomfort or pain and numbness at the dorsal, lateral and ventral sides of the penile shaft. Although the data do not allow further subdivision based on the extent of skin removed, it appears plausible to assume that the circumcision technique can influence penile sensitivity: the more skin is removed, the higher is the risk of discomfort and numbness. Circumcised men reported higher orgasm intensity related to stimulation of the ventral side of the penile shaft. This observation might endorse the importance of the dense nerve content of the frenulum and preputium.

Overall Penile Sensitivity

The present results contrast with the findings of the study by Krieger et al. 16, in which circumcised men reported increased overall sensitivity and increased ease of reaching orgasm. The latter study was prospective; it randomised men 1 : 1 to either immediate circumcision or to circumcision delayed by 2 years (control group). Both groups were evaluated at 1, 3, 6, 12, 18, and 24 months after baseline (circumcision in the case of the target group) with a questionnaire consisting of six questions on sexual function and sexual pleasure. Overall penile sensitivity was assessed by means of only a single variable. By contrast, the respondents in the present study rated the sensitivity of different areas of the penis as illustrated in detailed graphs, which may have enhanced the reporting accuracy. In addition, one needs to consider that a 2‐year follow‐up period may be too short to detect possible long‐term desensitisation of the glans nerves.

In the present study, orgasm was assessed by two different variables, ‘orgasm intensity’ and ‘effort to reach orgasm’. Circumcised and uncircumcised men did not differ in the rating of ‘effort needed to reach orgasm’. Krieger et al. 16 assessed orgasm by means of one single variable, ‘ease of reaching orgasm’, which yielded a significant difference compared with before they were circumcised, 64.0% of circumcised men reported their penis was ‘much more sensitive’, and 54.5% rated their ease of reaching orgasm as ‘much more’ at month 24. In a similar randomised clinical trial involving 2210 immediately circumcised men and 2246 men circumcised after a delay of 24 months, Kigozi et al. 31 found that men reported increased penile erotic sensitivity shortly after circumcision, but the authors did not assess long‐term effects. Different, conflicting results of circumcision were also reported by studies using the Brief Male Sexual Function Inventory (BMSFI), possibly due to the limitations of the BMSFI 32-34. The five domains of the BMSFI (sexual drive, erections, ejaculation, problem assessment and overall satisfaction) may be too unspecific for the assessment of somatosensory differences between circumcised and uncircumcised men. The more specific items of a questionnaire like the SAGASF‐M are more likely to capture inter‐individual variations in penile sensitivity.

Compared with previous studies where no effects between childhood and adult circumcision were found, in the present study, men circumcised after puberty reported less sexual pleasure at the dorsal side of the glans penis and more discomfort and pain at the penile shaft 13. The large sample size and detailed assessment of the present study may have accentuated this result. The loss of sexual pleasure could be explained by the desensitisation of the dorsal glans penis nerves. In men circumcised before puberty, the subsequent pubertal growth process possibly compensates post‐circumcision shortages of the penile skin.

In addition to the above mentioned differences in assessment technique (including the number of variables assessed) and in study design (prospective vs retrospective), there are also differences in the study populations. Krieger et al. 16 conducted their study in Kenya, while the present study took place in Belgium. Cultural differences, particularly in views on sexuality, may influence the interpretation of questions. The fact that circumcision is traditional in most Kenyan populations is likely to create a major cultural bias. Circumcision is considered a rite of passage in Kenya and distinguishes man from boy. This probably biases how men perceive sexuality.

The present study describes a decrease in erotic sensitivity with increasing age in both circumcised and uncircumcised men. Taylor et al. 35 confirms the present finding of a reduction in penile sexual pleasure with increasing age. This is attributed to the fact that in older men the ridged band becomes smoother. Activation of the bulbocavernosus and bulbospongiosus reflex by stretching of the ridged band of the foreskin has been described and could improve sexual pleasure. Since in older men this structure is smoother, there is less possibility of the structure to stretch and activate this reflex. In the present study the same ageing effect was also seen in circumcised males. A general decline in somatosensory nerve activity with ageing has been described and could be responsible for this observation 36. In the present study, the same ageing effect was also seen in circumcised males.

A major strength of the present study is its large sample size. However, the sample is not representative of the general male population, but biased towards highly educated men. We do not yet know whether the findings would persist in a sample of men with a lower education level, who may find a lengthy written self‐report questionnaire more challenging. Yet, we would expect that the ample use of illustrations in the SAGASF‐M would greatly support accuracy of reporting also by men of lower educational level and avoid problems such as those noted by Risser et al. 37. Many participants in their self‐evaluation survey could not identify correctly whether or not they were circumcised.

In future research, adding questions about frequencies and type of sexual practices, as well as the time needed to reach orgasm, may further refine our understanding of the effects of circumcision. Self‐report by way of the SAGASF‐M along with somatosensory testing of the same subjects would possibly constitute an ideal set of complementary tools for assessing penile erotic sensitivity. Future longitudinal pre‐ and post‐circumcision designs may further strengthen the results of the present study. Such a combination of methods is planned for a future investigation.

The findings from the present study underline the important role played by the foreskin for penile sensitivity and functioning and for men's overall sexual satisfaction. Adult men, as well as parents considering circumcision of their sons, should always be informed of the role of the foreskin in male sexuality, before their decision for surgery. The present findings should also be taken into consideration in the evaluation of the recently introduced practice of circumcision for the prevention of sexually transmitted infections, e.g. HIV and penile cancer 38.