THE CONDITIONS

The following detailed anatomical descriptions, may tire some readers, if so please turn to the central discussion.

ADHESIONS
The foreskin may stick to the glans, it may stick partially, it may also restick after being released.
This condition is normal and healthy in babies. Generally it resolves of its own accord by the age of three, however sometimes the condition continues up until puberty.
There are different degrees of adhesion. Some boys release the foreskin themselves at the beginning of puberty, others experience intense pain when they attempt to do this. (Bettelheim reports a case4 where during masturbation adhesions "had been partly painful"5. )
Note: I believe that when adhesions release at a later age (e.g. at ten years old) the foreskin develops less elasticity, and this results in a tight foreskin.

PHIMOSIS
(Greek phimos : a muzzle, nose band of a bridle).
A thin white ring of connective tissue around the end of the foreskin, about a third of an inch from the end, narrows the opening of the foreskin and restricts its elasticity. This hinders the retraction of the foreskin over the coronal ridge and behind the glans. Any difficulty when flaccid is magnified when erect.

A Matter of Degree
The ring varies in narrowness. Very extreme degrees often cause urinary complications or infections, and are discovered in childhood.

For the adolescent, the effect when erect, is similar to trying to take a T-shirt off by pulling it down. During intercourse, when the narrowness is extreme, (depending also on the degree of lubrication and openness of the vagina), the foreskin can ruffle up, to form a barrier.
If it is possible to retract the foreskin, with a partial phimosis, the passage over the coronal ridge of the glans may be painful, the abrasion may cause inflammations and as the process continues these may lead to infections. There is also the danger of a secondary condition called paraphimosis : when the foreskin is held trapped behind the glans, this is a medical emergency. There are also some mild degrees, which are unnoticeable when flaccid.

Statistics
If the statistics were only 1%, this would be too many.
Medical Studies
Medical attention is concentrated on phimosis, because with a phimosis cleaning is severely hindered, and the area between the foreskin and glans offers an ideal environment for disease and bacterial infection. In a study of "3,000 young men, mostly of an age between 18 and 22 . ." (all over 16) " . . A phimosis was found in 8.8%" 6. A second study was on schoolboys between the ages of 14 and 19. Examining if "the foreskin could be retracted only with difficulty or with pain", it was found among "229 youths that 20 had these problems. This corresponds to a frequency of 8.7%" 7.

Age Groups
In one study specifically on congenital phimosis, the operation was performed on 40 men at the following ages8.