According to this article about porn-induced erectile dysfunction, it is important to know that human brain works to be able to understand why watching excessive amounts of porn can lead to erectile dysfunction.
Neurons are cells that receive and send messages between the body and the brain. The brain has many neurons, which are the basic working units of the nervous system.
Neurotransmitters send chemical messages between the neurons. A neurotransmitter called dopamine helps the flow of information to the front of the brain, which is linked to thought and emotion. It is also linked to reward systems.
If a person receives a hug, the brain releases dopamine, which makes the person feel good. A person's response to natural rewards such as sex are largely regulated by the dopamine pathway as well.
Porn-induced erectile dysfunction is dependent on the activation of this pathway. This neurotransmitter signaling plays a crucial role in sexual arousal and porn-induced erectile dysfunction.