Phimosis is a tightening of the foreskin that normally folds over the penis. This tightening may squeeze the penis, which may swell until it cuts off blood flow, damaging the tissue.

Phimosis usually is caused by infection and scarring, but it may be present at birth (congenital). Once the foreskin tightens, returning it to its normal position over the head of the penis may become difficult or impossible.

Correcting phimosis often requires surgery to remove the foreskin (circumcision).