Researchers were assessing prostate cancer risk. Men could reduce their risk of developing prostate cancer through regular masturbation, researchers suggest. They say cancer-causing chemicals could build up in the prostate if men do not ejaculate regularly. And they say sexual intercourse may not have the same protective effect because of the possibility of contracting a sexually transmitted infection, which could increase men's cancer risk. Australian researchers questioned over 1,000 men who had developed prostate cancer and 1,250 who had not about their sexual habits. They found those who had ejaculated the most between the ages of 20 and 50 were the least likely to develop the cancer. The protective effect was greatest while the men were in their 20s. Men who ejaculated more than five times a week were a third less likely to develop prostate cancer later in life.