It wasn’t very long ago that doctors and researchers believed that in order for something to be addictive, it had to involve an outside substance that you physically put into your body, like cigarettes, alcohol, or drugs.
Pornographers promise healthy pleasure and relief from sexual tension, but what they often deliver is an addiction, tolerance, and an eventual decrease in pleasure.
—Norman Doidge, MD, The Brain That Changes Itself 
It wasn’t very long ago that doctors and researchers believed that in order for something to be addictive, it had to involve an outside substance that you physically put into your body, like cigarettes, alcohol, or drugs. 
Once we got a peek into the brain, however, our understanding of how addictions work changed.  It turns out, cigarettes, alcohol, and drugs have more in common than you might think. Sure, on the outside, some are poured into a glass while others are lit on fire and smoked. But once they’re in the body, they all do the same thing to the brain: flood it with a chemical called dopamine.  That’s what makes them addictive. And porn does the exact same thing. 
You see, your brain comes equipped with something called a “reward pathway.”  Its job is to motivate you to do things that keep you and your genes alive—things like eating or having sex to produce babies.  The way it rewards you is by releasing dopamine into your brain, because dopamine makes you feel good. 
However, just because your brain has adapted to motivate you to do something doesn’t mean it’s always good for you. For example, your brain produces higher levels of dopamine when you have chocolate cake than it does for whole-wheat bread.  Why? Because 3,000 years ago, high-calorie foods were really hard to come by, so when our ancestors found them, it was important that they eat a whole bunch while the getting was good.  These days, a bag of Oreos is only as far as the nearest supermarket. If we gorged on them every chance we got, chances are we’d get heart disease, gain weight, and develop a bunch of other health problems.
Porn is basically sexual junk food. When a person is looking at porn, their brain thinks they’re seeing a potential mating opportunity, and pumps the brain full of dopamine.  And unlike healthy sexual relationships that build up over time with an actual person, porn offers an endless stream of hyper-sexual images that flood the brain with high levels of dopamine every time the user clicks to a new image. 
Setting your brain up for an overload of feel-good chemicals might sound like a good idea at first, but just like with junk food, what feels like a good thing, in this case isn’t at all. Because porn use floods the brain with high chemical levels, the brain starts to fight back. Over time, the brain will actually cut down on its dopamine receptors—the tiny landing docs that take the dopamine in once it’s been released in your brain.  As a result, porn that once excited a person often stops having the same effect, and the user has to look at more porn, look at porn more often, or find a more hardcore version—or all three—to get aroused. 
Eventually, as the brain acclimates to the overload of dopamine, users often find that they can’t feel normal without that dopamine high.  Little things that used to make them happy, like seeing a friend or playing their favorite sport, can’t compete with the dopamine flood that comes with porn, so they’re left feeling anxious or down until they can get back to it. 
On top of that, dopamine doesn’t travel alone. When the brain is getting a hit of dopamine, it’s also getting new pathways built into it with a protein called “iFosB” (pronounced delta fos b). 
Essentially, iFosB’s job is to help you remember to do things that feel good or are important.  While dopamine is motivating your brain to do things and rewarding it for doing them, iFosB is quietly leaving trail markers in your brain, creating a pathway to help you get back there.  When this happens with healthy behaviors, it’s a very good thing. However, as little as one dose of many drugs will also cause iFosB to start building up in the brain’s neurons, and of course porn’s powerful dopamine surge causes iFosB to build up as well. 
The more a user looks at porn, the more iFosB accumulates,  essentially beating down the brain pathways leading to using, making it easier and easier for the user to turn back to that behavior, whether they want to or not.  Eventually, if enough iFosB accumulates, it can “flip a genetic switch,” causing irreversible changes in the brain that leave the user more susceptible to addiction. 
And for teens, the risks are especially high, since a teen brain’s reward pathway has a response two to four times more powerful than an adult brain—which means teen brains release even higher levels of dopamine.  Teen brains also produce higher levels of iFosB, leaving them extra vulnerable to addiction. 
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