text: There are many causes for penis curvature.  These include weak and poor development of the penis, wearing restrictive underwear, a penis injury or some form of damage to the penis, age, over-masturbation resulting in trauma to the penis causing scar tissue to form and thus causing the penis to gradually curve, twist, or bend.  Other results include the penis being out of shape or deformed, such as one part being thicker or thinner than another part.  A slight curve such as to only 15 degrees, however, is normal.