In fact, it is a very controversial subject and according to the different anatomical studies, according to the regions of the world and the ethnic groups, the results differ greatly. On this subject, it is necessary to exclude for the statistics those who mainly practice ritual or medical circumcision without obligation. Asians, as mentioned in this thread, very often have a shorter foreskin than Europeans in general. But the aspects can be misleading outside of a study of strict medical measures, because the cultural aspect can play a role. Thus, in Japan, young boys, from the age of 7/8, are taught to keep the glans uncovered permanently; it is both cultural (politeness) and hygienic. In fact, during puberty, the foreskin tends to grow less, having been held since childhood in position behind the glans corona. Thus, many Japanese adults have a short or even very short foreskin, with an exposed glans. In Europe, where this custom does not exist, it is more common to have variations in the length of the foreskin. As also mentioned in this thread, generally all little boys before puberty have a long foreskin that extends in front of the glans, which is called the "foreskin overhang". During puberty, depending on generally genetic factors, the glans develops more or less, accompanied by a greater or lesser lengthening of the foreskin. All these combinations are found with extremely variable final results in adulthood. About 10% of adult men retain a long foreskin with an overhang. Another 10% have a long foreskin but without an overhang, with the preputial ring more or less open through which the glans and the urinary meatus can be seen. Then the vast majority, 75% of uncircumcised men, have an "average" foreskin covering the glans from 10 to 80% of its surface. So we can say that as a general rule, the foreskin does not cover the glans entirely, but with a great variety, the glans can appear slightly, on 1/4, 1/3, half of its length up to 80%. And there are still 5% of men in whom the foreskin is too short to cover the glans. Men with a short foreskin covering less than 20% of the glans tend to remain permanently uncovered and to appear in a similar aspect to a circumcised man.
Finally, there remains another variation to take into account is that of temperature. The colder it is, the more the penis retracts. And in fact, the more the foreskin covers the glans. The same penis can appear with a glans covered at 80% at room temperature (15°/20°) and be completely covered when leaving a bath in cold water. Similarly, the same penis can appear half-uncovered or even completely uncovered in very hot weather (35° and +).
Finally, one last element that can play not on the actual length of the foreskin but on its position, on the glans or behind the glans (uncovered) is the fact of having the frenulum intact or not. It is common for the frenulum to be broken during sexual life, or cut voluntarily for various reasons, medical or not. When the frenulum is no longer there to have its function of "return spring" of the foreskin, the latter has a greater tendency to remain in its position. So much so that after sexual intercourse, it will not necessarily return to the glans when the penis becomes flaccid again. This explains why men who are fans of "Bare Glans" (a movement of men who voluntarily keep the glans uncovered) have very often removed their frenulum. And this also explains certain preconceived ideas, which have given rise to popular beliefs, particularly in Western Europe; the frenulum being often subject to its tear or its complete rupture sometimes during the first or one of the first sexual intercourses, this has been assimilated to "male deflowering". Subsequently, the glans remaining more easily and more frequently uncovered, certain beliefs in less educated circles gave rise to a myth in the countryside: that according to which once deflowered (meaning once the frenulum is broken) the man having lost his virginity keeps the glans uncovered permanently. This is of course false as a general rule, but myths die hard! These popular images have sometimes influenced even certain general practitioners ... this is also supported by pornographic imagery where it is very rare to see men with the glans covered by the foreskin.
