A very pronounced curve occurs in a condition called Peyronie's disease. Although it is not certain, it is thought to be caused by the development of hard, fibrous, inflamed tissue in the shaft of the penis, and usually starts as pain during erection, caused by stretching of inflamed penile tissue.
As the disease progresses, the pain subsides, and then fibrous tissue develops, causing the penis to curve to the left, right, or upward. The majority of cases of Peyronie's disease require medical attention and are generally curable.
Another erectile disorder, priapism, is the continual and pathological erection of the penis. It is usually caused by nonsexual factors such as spinal cord disease, leukemia or sickle cell disease, and, according to some reports, with the use of cocaine. Sometimes it happens for no known reason.
In cases of priapism, the increased blood flow that causes an erection is unable to drain from the penis in the usual way because the release mechanism has been broken down by the disease or affected by drugs or other unknown factors. It is extremely painful and may require surgery if the problem does not respond to medical treatment. Certain non-medical circumstances, such as painful stimulation of the penis, or disturbed emotional states such as fear, anger, guilt, anxiety, or shame can cause a man to lose his erection or prevent him from getting an erection in the first place. Emotional difficulties and the anticipation and worry about possibly losing an erection are common causes of a man's erectile difficulties.