One of the main hallmarks of an addiction process involves changes in dopamine receptor numbers and types on key nerve cells in the brain. To hear the message, dopamine attaches to receptors on cells. With addiction, some types of receptors decrease, while other types increase. We focus on dopamine (D2) receptor, as it decreases, causing the reward circuitry to become "numbed". This leads to cravings and repeated porn use.
This section contains both lay articles for the general public, and research articles. If you are not an expert in addiction, I suggest starting with the lay articles, they are marked with an "L"