The foreskin is the double-layered fold of smooth muscle tissue, blood vessels, neurons, skin, and mucous membrane part of the penis that covers and protects the glans penis and the urinary meatus.
Purpura et al. (2018) describe the foreskin as follows:
Few parts of the human anatomy can compare to the incredibly multifaceted nature of the human foreskin. At times dismissed as “just skin,” the adult foreskin is, in fact, a highly vascularized and densely innervated bilayer tissue, with a surface area of up to 90 cm, and potentially larger. On average, the foreskin accounts for 51% of the total length of the penile shaft skin and serves a multitude of functions. The tissue is highly dynamic and biomechanically functions like a roller bearing; during intercourse, the foreskin “unfolds” and glides as abrasive friction is reduced and lubricating fluids are retained. The sensitive foreskin is considered to be the primary erogenous zone of the male penis and is divided into four subsections: inner mucosa, ridged band, frenulum, and outer foreskin; each section contributes to a vast spectrum of sensory pleasure through the gliding action of the foreskin, which mechanically stretches and stimulates the densely packed corpuscular receptors. Specialized immunological properties should be noted by the presence of Langerhans cells and other lytic materials, which defend against common microbes, and there is robust evidence supporting HIV protection. The glans and inner mucosa are physically protected against external irritation and contaminants while maintaining a healthy, moist surface. The foreskin is also immensely vascularized and acts as a conduit for essential blood vessels within the penis, such as supplying the glans via the frenular artery.
- 1 Structure
- 2 Physiological functions
- 3 The role of the foreskin in heterosexual relations
- 4 See also
- 5 External links
- 6 References
Foreskin in infancy and childhood
Baby boys are born with the foreskin fused with the glans penis by the balanopreputial lamina, a synechial membrane, which prevents retraction. In addition, the tip of the foreskin (acroposthion) is usually too narrow to allow retraction of the foreskin. The preputial cavity is closed by the synechia and cannot be infected.
Forcible attempts to retract the foreskin result in injury to the boy, so should be avoided. The first person to retract the foreskin should be the boy himself.
Thorvaldsen & Meyhoff (2005) conducted a survey of 4,000 boys in Denmark. They report that the mean age of first foreskin retraction is 10.4 years in Denmark.
Foreskin in adulthood
The foreskin (also known as the prepuce) is the double-layered fold of smooth muscle tissue, blood vessels, neurons, skin, and mucous membrane part of the penis that covers and protects the glans penis and the urinary meatus. The adult foreskin measures about 3 inches by 5 inches or 15 square inches. The two foreskin layers provide a skin reserve. When the penis becomes erect, the foreskin may wholly or partially unfold to provide the necessary skin to allow for expansion of the penis during erection.
The foreskin is the movable part of the penis. The foreskin is not attached to the underlying structure and is free to glide back and forth. The gliding action reduces the friction of intercourse and helps to prevent abrasions, while conserving vaginal lubrication and moisture.
The epithelium of the outer layer of the foreskin is true skin while the epithelium of the inner layer is mucosal membrane. There is a mucocutaneous boundary at the tip of the foreskin. The mucocutaneous junction is a specific erogenous zone.
The layer of dartos muscle is contained within the foreskin. The dartos muscle keeps the foreskin snugly against the glans. The fibers of the dartos muscle form a whorl at the tip that functions as a sphincter. The sphincter opens to allow urine to flow out, but closes to protect the penis from foreign matter, contaminants, and pathogens.
As with other neurologic structures such as the brain, the tip of the prepuce is richly supplied with blood by important vascular structures. The prepuce serves as a conduit for several important veins. The glans penis receives blood through the frenular artery.
The foreskin provides physical protection to the glans penis and inner mucosa, protecting the mucosal tissue from pathogens, pollutants, friction, injury, and drying out. The foreskin protects the glans penis and meatus of infant boys from abrasion and irritation from ammoniacal diapers. 
In the absence of the foreskin about ten to twenty percent of boys suffer urethral stricture (meatal stenosis) requiring further treatment. Frisch & Simonsen (2016) reported the incidence of meatal stenosis to be 3.7 times higher in circumcised boys.
Fleiss et al. (1998) have listed numerous immunological functions of the foreskin that help to protect the human body against infection. The foreskin maintains the moistness of the preputial mucosa and the glans penis by transudation. The sub-preputial moisture contains cathepsin B, chymotrypsin, neutrophil elastase, cytokines, and lysozyme, which has the capacity to desttroy the cell walls of bacteria. The preputial muscles keep the tip of the foreskin closed to keep out pathogens.
The foreskin is highly vascularized. The high rate of blood flow helps to prevent infection.
Although claims have been made that the presence of the foreskin increases the risk of infection with human immune deficiency virus (HIV), that is not correct. The claims are based on the reported findings of three randomized clinical trials (RCTs) that were carried out more than a decade ago in Africa. Boyle & Hill (2011) have shown these RCTs to be have significant methodological flaws and statistical errors that render their claims invalid.
Fleiss et al. noted the presence of Langerhans cells in the prepuce. De Witte et al. (2007) have discovered that Langerhans cells produce Langerin, which is a "natural barrier to HIV infection".
The gliding action facilitates intromission.  During the thrusting of sexual congress, the gliding action reduces abrasions and irritation in the female partner and avoids problems with vaginal dryness.
Nature designed the foreskin to be an erogenous sensory organ. The foreskin has a layer of muscle called the dartos muscle sheath that provides the foreskin with elasticity, flexibility, and stretchiness, which allows full stimulation of the nerves in the ridged band that sense movement and stretching. There is a mucocutaneous region at the tip of the foreskin where outer skin changes to inner mucosa. Winklemann (1959) identified the foreskin as a specific erogenous zone (meaning an area of acute erogenous sensation). Winklemann reported rete ridges in the foreskin with nerves set close to the surface with closely set networks.
Lakshamanan & Prakash (1980) report the "prepuce covers the glans completely and snugly like a hosiered material and continues to do so through the entire span of life of the male", which they explain as being caused by the smooth muscle fibers within the prepuce. The prepuce is free to glide back and forth. When it does, it must stretch to go over the glans penis.
Taylor et al. (1996) carried out a histological study of the foreskin. (Histology is the microscopic examination of cells and tissues.) Taylor et al. found an area of rete ridges just inside the tip of the foreskin that he called the ridged band. The ridges were found to have nerve endings at the top of the ridges. They report that the ridged band area moves to the shaft of the penis when the penis becomes erect where the nerves are subject to stimulation. They stated:
The prepuce provides a large and important platform for several nerves and nerve endings. The innervation of the outer skin of the prepuce is impressive; its sensitivity to light touch and pain are similar to that of the skin of the penis as a whole.
Sorrells et al. (2007) conducted a fine-touch study of the penis of both circumcised and intact men. Sorrells et al. concluded:
In conclusion, circumcision removes the most sensitive parts of the penis and decreases the fine-touch pressure sensitivity of glans penis. The most sensitive regions in the uncircumcised penis are those parts ablated by circumcision. When compared to the most sensitive area of the circumcised penis, several locations on the uncircumcised penis (the rim of the preputial orifice, dorsal and ventral, the frenulum near the ridged band, and the frenulum at the muco-cutaneous junction) that are missing from the circumcised penis were significantly more sensitive.
Bronselaer et al. (2013) surveyed a large group of intact and circumcised men in Belgium. They reported:
Of the men in Group A [intact males], 90.6% rated the sexual pleasure provided when the foreskin was stimulated by themselves or their partners from ‘mild’ to ‘very strong’ and 61.9% the respective orgasm from ‘mild’ to ‘very strong’.
For the glans penis, men in Group B [circumcised males] reported significantly less sexual pleasure than men in Group A at the dorsal side (P ≤ 0.001), and the lateral (P ≤ 0.001) and ventral sides (P = 0.02). Orgasm was less intense in Group B at the dorsal side (P = 0.006) and at the lateral sides (P = 0.02). Group B required more effort in achieving orgasm at the lateral sides (P = 0.04). Furthermore, a larger percentage of men in this group reported numbness at the dorsal, lateral, and ventral sides (all P ≤ 0.001), as well as unusual sensations (burning, prickling, itching, or tingling) at the lateral sides (P = 0.02) and at the ventral side (P = 0.003) of the glans.
Laumann et al. (1997) report that men who lack a foreskin "engage in a somewhat more elaborated set of sexual practices than do men who are not circumcised. For each of the practices examined, lifetime experience of various forms of oral and anal sex and masturbation frequency in the past year, circumcised men engaged in these behaviors at greater rates. The difference between circumcised men was greatest for masturbation - ironically, a practice that circumcision was once thought to limit. A total of 47% of circumcised men reported masturbating at least once a month vs 34% for their uncircumcised peers." Dave et al. (2003) reported that men without foreskins "were more likely to report having had homosexual partner(s) (7.5% v 5.3%, p =0.012) and partners from abroad (19.7% v 13.1%, p...0.001)."
Cold & Taylor (1999) commented, "The increased frequency of masturbation, anal intercourse and fellatio reported by circumcised men in the USA may possibly be due to the sensory imbalance caused by circumcision. Clearly, amputation of the prepuce causes changes in sexual behaviour in human males and females.
Frisch et al. (2013) surveyed the sexual function and behavior of a large group of intact and circumcised men in Denmark. They reported that "circumcised men were more likely (38%) than uncircumcised men (28%) to report ≥10 sex partners."
The role of the foreskin in heterosexual relations
The knowledge of the important of the intact penis in heterosexual relations long has been known to the Jews who give us our earliest evidence of the value of the foreskin to the female partner.
Moses Maimonides, a Jewish rabbi and physician, stated in the 12th century:
According to the Rabbi Isaac ben Yedaiah, who lived in Southern France in the late 13th century:
She too will court the man who is uncircumcised in the flesh and lie against his breast with great passion, for he thrusts inside her a long time because of his foreskin, which is a barrier against ejaculation in intercourse. Thus she feels pleasure and reaches an orgasm first. When an uncircumcised man sleeps with her, and then resolves to return to his home, she brazenly grabs him, holding on to his genitals and says to him, "Come back, make love to me." This is because of the pleasure that she finds in intercourse with him, from the sinews of his testicles—sinew of iron—and from his ejaculation—that of a horse which he shoots like an arrow into her womb. They are united without separating, and he makes love twice and three times in one night, yet the appetite is not filled.
As previously reported, the foreskin reduces the force required for penetration of the female partner's vagina by as much as ninety percent. The gliding action of the foreskin reduces friction and abrasion, while conserving vaginal lubrication.
In a first of its kind, O'Hara & O'Hara (1999) carried out a retrospective surevy of 138 women with experience of both intact and circumcised partners. The women overwhelmingly concurred that the mechanics of coitus was different for the two groups of men. Of the women, 73% reported that circumcised men tend to thrust harder and deeper, using elongated strokes, while unaltered men by comparison tended to thrust more gently, to have shorter thrusts, and tended to be in contact with the mons pubis and clitoris more, according to 71% of the respondents. Women with intact partners had a higher rate of orgasms than women with circumcised partners. O'Hara & O'Hara concluded:
Clearly, the anatomically complete penis offers a more rewarding experience for the female partner during coitus. While this study has some obvious methodological flaws, all the differences cannot be attributed to them. It is important that these findings be confirmed by a prospective study of a randomly selected population of women with experience with both types of men. It would be useful to examine the role of the foreskin in other sexual activities. Because these findings are of interest, the negative effect of circumcision on the sexual enjoyment of the female partner needs to be part of any discussions providing 'informed consent' before circumcision.
Solinis & Yiannaki (2007) concluded; "[t]here was a decrease in couple’s sexual life after circumcision indicating that adult circumcision adversely affects sexual function in many men or/and their partners, possibly because of complications of surgery and loss of nerve endings."
Morten et al. (2013) surveyed a very large group of men and women in Denmark. They concluded:
"Circumcision was associated with frequent orgasm difficulties in Danish men and with a range of frequent sexual difficulties in women, notably orgasm difficulties, dyspareunia and a sense of incomplete sexual needs fulfilment."
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To provide informed, respectful care to males with intact genitals, and to fully understand the harms of circumcision, health professionals must have a thorough grasp of the anatomy, development, and functions of the foreskin (also known as the prepuce).
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