When the penis is in a state of weakness, the foreskin should be located above the coronary sulcus, which can be easily turned up or down, but sometimes it is difficult to reset after the foreskin is turned down. The foreskin mouth just tightens the coronal groove of penis, which hinders the blood return of the distal foreskin and glans penis, resulting in swelling of these parts. This condition is called foreskin incarceration.

If the foreskin is too long, phimosis will easily cause the foreskin to be incarcerated, and the external opening is too small to be turned over, which is called phimosis. If phimosis patients forcibly turn up the foreskin, the foreskin clasp will be stuck in the crown groove of penis, forming a tight annular band, which will then hinder the blood circulation of glans penis, which will cause edema of glans penis for a long time, and in severe cases, ischemic necrosis of distal end will occur. The phimosis is suddenly incarcerated, and the penis head and foreskin are edema, and the pain is obvious.