The outside of the foreskin is like the skin on the shaft of the penis but the inner foreskin is a mucous membrane like the inside of the eyelid or the mouth. Like the eyelid, the foreskin is free to move after it separates from the glans, usually by puberty. Smooth muscle fibres keep it close to the glans but make it highly elastic. The foreskin is attached to the glans with a frenulum which helps retract the foreskin over the glans. At the end of foreskin there is a band of tissue called the ridged band which, according to one study, is rich in nerve endings called Meissner's corpuscles. According to a study by Sorrells et al., the five most sensitive areas of the penis are on the foreskin.
In children, the foreskin covers the glans completely but in adults this need not be so. Schöberlein found that about 50% of young men had full coverage of the glans, 42% had partial coverage, and in the remaining 8%, the glans was uncovered. After adjusting for circumcision, he stated that in 4% of the young men the foreskin had spontaneously atrophied (shrunk).
At birth, the foreskin is usually still fused with the glans. As childhood progresses the foreskin and the glans gradually separate, a process that may not be complete until late puberty. Thorvaldsen and Meyhoff reported that average age of first foreskin retraction in Denmark is 10.4 years. Wright argues that forcible retraction of the foreskin should be avoided and that the child himself should be the first one to retract his own foreskin. Premature retraction may be painful, and may result in infection.
Taylor et al described the foreskin in detail, documenting a ridged band of mucosal tissue. They stated "This ridged band contains more Meissner's corpuscles than does the smooth mucosa and exhibits features of specialized sensory mucosa. In 1999, Cold and Taylor stated "The prepuce is primary, erogenous tissue necessary for normal sexual function." Boyle et al, state that "The complex innervation of the foreskin and frenulum has been well-documented, and the genitally intact male has thousands of fine touch receptors and other highly erogenous nerve endings—many of which are lost to circumcision, with an inevitable reduction in sexual sensation experienced by circumcised males. The AAP noted that the work of Taylor et al "suggests that there may be a concentration of specialized sensory cells in specific ridged areas of the foreskin.
Moses and Bailey (1998), describe the evidence of sensory function as "indirect," and state that "aside from anecdotal reports, it has not been demonstrated that this is associated with increased male sexual pleasure. The World Health Organisation states that there is little evidence for diminished sexual function, adding that studies have been inconsistent. Fink et al. reported "[a]lthough many have speculated about the effect of a foreskin on sexual function, the current state of knowledge is based on anecdote rather than scientific evidence." Masood et al. state that "[c]urrently no consensus exists about the role of the foreskin or the effect circumcision has on penile sensitivity and overall sexual satisfaction." Schoen states that "[a]necdotally, some have claimed that the foreskin is important for normal sexual activity and improves sexual sensitivity. Objective published studies over the past decade have shown no substantial difference in sexual function between circumcised and uncircumcised men.
The term 'gliding action' is used in some papers to describe the way the foreskin moves during sexual intercourse. This mechanism was described by Lakshamanan & Prakash in 1980, stating that "[t]he outer layer of the prepuce in common with the skin of the shaft of the penis glides freely in a to and fro fashion... Several opponents of circumcision have argued that the gliding movement of the foreskin is important during sexual intercourse. Warren & Bigelow claim that gliding action would help to reduce vaginal dryness and that restoration of the gliding action is an important advantage of foreskin restoration. O'Hara describes the gliding action, stating that it reduces friction during sexual intercourse, and suggesting that it adds "immeasurably to the comfort and pleasure of both parties". Taylor suggests that the gliding action, where it occurs, may stimulate the nerves of the ridged band, and speculates that the stretching of the frenulum by the rearward gliding action during penetration triggers ejaculation.
Taves used a single subject to test the actual force required to penetrate a measuring apparatus. When the foreskin was retracted a more than tenfold increase in force was needed. He argued that this confirms the belief of Morgan (1967) that the foreskin makes sexual penetration easier during sexual intercourse. Whiddon (1953) and Foley (1966) also believed that the presence of the foreskin made sexual penetration easier.
The fold of the prepuce maintains sub-preputial wetness, which mixes with exfoliated skin to form smegma. Some authors believe that smegma contains antibacterial enzymes, though their theory has been challenged. The American Academy of Pediatrics state that "No controlled scientific data are available regarding differing immune function in a penis with or without a foreskin. Inferior hygiene has been associated with balanitis, though excessive washing can cause non-specific dermatitis.
Non-retractable foreskin is not always indicative of a clinical condition. The first time the foreskin retracts (say during masturbation or sex) can be a slightly painful experience as the glans penis is not used to friction and air contact. However the problem resolves itself after a few days of acclimatization, which may include consciously retracting the foreskin and exposing it to air, water or friction.
A condition called paraphimosis may occur if a tight foreskin becomes trapped behind the glans and swells as a restrictive ring. This can cut off the blood supply, resulting in ischaemia of the glans penis.
Aposthia is a rare condition in which the foreskin is not present at birth.
Preputioplasty is a procedure to relieve a tight foreskin without resorting to circumcision.
Other practices include genital piercings involving the foreskin and slitting the foreskin.
Foreskins from circumcised babies are used to make a commercial anti-wrinkle skin cream. A six-week supply costs US$130.
Foreskin fibroblasts have been used in biomedical research.