Is either excessive masturbation or excessive porn use leading to social anxiety in some individuals?
Dopamine surges during sexual arousal and drops after climax. Do some people masturbate so frequently that their reward circuitry is unable to return to homeostasis between orgasms? Are they suffering from chronically low dopamine (or low response to dopamine)—making social anxiety more likely? It’s important to realize that masturbation frequencies in modern Western society may have little resemblance to our hunter-gatherer ancestors (see WEIRD Masturbation Habits).
If not masturbation, then heavy porn use can certainly lead to a decline in dopamine and dopamine receptors in some brains. All addictions, including behavioral addictions such as pathological gambling and Internet gaming, cause a measurable decline in dopamine signaling. If you have a porn addiction, you have what we call a numbed pleasure response or desensitization, which means low dopamine signalling. (See: Porn Then and Now: Welcome to Brain Training and Intoxicating Behaviors: 300 Vaginas = A Lot of Dopamine to understand the mechanisms.)