In an uncircumcised male, the head of the penis is covered by a sheath of skin known as the foreskin. Phimosis is a condition in which the foreskin is tightly stretched around the head of the penis and cannot be pulled back freely. Phimosis can occur naturally. For example, in boys younger than age 4, it is normally hard to pull back the foreskin. However, in older boys and men, phimosis often is triggered by an infection under the foreskin (balanitis) or by other medical conditions such as diabetes.
Paraphimosis occurs when a tight foreskin is pulled back behind the head of the penis and then becomes stuck. It cannot be placed forward again to its usual position covering the tip of the penis. This can cause swelling, pain, and loss of blood flow to the tip of the penis. If the foreskin cannot be pushed back into its natural position, serious harm can occur.