What is the cause of impotence in bed?

Patient's question:

Male, 22 years old

Doctor's answer:

Erectile dysfunction (ED) is defined as the persistent inability to achieve or maintain an erection sufficient for sexual activity. ED is more accurate than the older term "impotence," as the latter carries certain derogatory connotations. ED can be classified into three degrees of severity: mild, moderate, and severe, with impotence belonging to the severe category of ED.
With the advancement of science and social progress, people's understanding of ED has deepened. For example, in the 15th century, ED was believed to be caused by demonic possession; in the 18th century, it was attributed to masturbation; in the early 19th century, it was considered purely a psychological disorder; and in the 1950s of this century, it was viewed as a behavioral disorder. It was not until the 1970s that the organic causes of ED were gradually recognized, leading to a better understanding of its physiology and pathology. Due to a lack of awareness about ED, many patients bear a heavy mental burden, affecting their normal family life and often making them more solitary and prone to irritability, which in turn impacts interpersonal relationships.
Before the 1970s of this century, ED was still believed to be related to reduced testosterone levels, natural aging, and psychological factors. However, after the 1970s, with the progress in research on the physiology and pathology of erection, people recognized that while psychological factors can indeed cause ED, for most men, ED is associated with various diseases (such as hypertension, diabetes, and cardiovascular diseases), medications, injuries, and surgeries. This is because the mechanism of erection involves the relaxation of smooth muscles in the corpora cavernosa of the penis, the dilation of penile arteries, increased blood flow, and obstruction of venous.