It's a truism that Facebook is the many-headed frenemy, the great underminer. We know this because science tells us so.
The Human-Computer Institute at Carnegie Mellon has found that your "passive consumption" of your friends' feeds and your own "broadcasts to wider audiences" on Facebook correlate with feelings of loneliness and even depression.
Earlier this year, two German universities showed that "passive following" on Facebook triggers states of envy and resentment in many users, with vacation photos standing out as a prime trigger.
Yet another study, this one of 425 undergrads in Utah, carried the self-explanatory title: "'They Are Happier and Having Better Lives Than I Am': The Impact of Using Facebook on Perceptions of Others' Lives."
Even the positive effects of Facebook can be double-edged: Viewing your profile can increase your self-esteem, but it also lowers your ability to ace an arithmetic task.
All of these studies are careful to point out that it's not Facebook per se that inspires states of disconnection, jealousy and poor mathematical performance - rather, it's specific uses of Facebook.
If you primarily use Facebook to share interesting news articles with colleagues, exchange messages with new acquaintances, and play Candy Crush Saga, chances are the green-eyed monster won't ask to friend you.
But if the hours you log on Facebook are largely about creeping through other people's posts - especially their photos, and especially their vacation snaps - with an occasional pause to update your own status and slap on a grudging "like" here or there, then science confirms that you have entered into a semi-consensual sadomasochistic relationship with Facebook and need to break the cycle.
A closer look at Facebook studies also supports an untested, but tantalizing hypothesis: that, despite all the evidence, Facebook is actually not the greatest underminer at the social-media cocktail party (that you probably weren't invited to, but you saw the pictures and it looked incredible). Facebook is not the frenemy with the most heads. That title, in fact, goes to Instagram. Here's why.
Instagram distills the most crazy-making aspects of the Facebook experience.
So far, academic studies of Instagram's effects on our emotional states are scarce. But it's tempting to extrapolate those effects from the Facebook studies, because out of the many activities Facebook offers, the three things that correlate most strongly with a self-loathing screen hangover are basically the three things that Instagram is currently for: loitering around others' photos, perfunctory like-ing, and "broadcasting" to a relatively amorphous group.
"I would venture to say that photographs, likes, and comments are the aspects of the Facebook experience that are most important in driving the self-esteem effects, and that photos are maybe the biggest driver of those effects," says Catalina Toma of the Department of Communication Arts at the University of Wisconsin-Madison.
"You could say that Instagram purifies this one aspect of Facebook."
Instagram is exclusively image-driven, and images will crack your mirror.
"You get more explicit and implicit cues of people being happy, rich and successful from a photo than from a status update," says Hanna Krasnova of Humboldt University Berlin, co-author of the study on Facebook and envy.
"A photo can very powerfully provoke immediate social comparison, and that can trigger feelings of inferiority. You don't envy a news story."
Krasnova's research has led her to define what she calls an "envy spiral" peculiar to social media.
"If you see beautiful photos of your friend on Instagram," she says, "one way to compensate is to self-present with even better photos, and then your friend sees your photos and posts even better photos, and so on. Self-promotion triggers more self-promotion, and the world on social media gets further and further from reality."
Granted, an envy spiral can unspool just as easily on Facebook or Twitter. But for a truly gladiatorial battle of the selfies, Instagram is the only rightful Colosseum.
Instagram messes more with your sense of time.
"You spend so much time creating flattering, idealised images of yourself, sorting through hundreds of images for that one perfect picture, but you don't necessarily grasp that everybody else is spending a lot of time doing the same thing." Toma says.
Then, after spending lots of time carefully curating and filtering your images, you spend even more time staring at other people's carefully curated and filtered images that you assume they didn't spend much time on. And the more you do that, Toma says, "the more distorted your perception is that their lives are happier and more meaningful than yours."
Again, this happens all the time on Facebook, but because Instagram is image-based, it creates a purer reality-distortion field.
Instagram ups your chances of violating "the gray line of stalkerism."
"If you don't know someone, and Facebook is telling you that you have interests in common," says Nicole Ellison of the University of Michigan School of Information, "you can see their profile as a list of icebreakers."
But that same profile is also a potential list of icemakers. If you meet a vague acquaintance at a party and strike up a conversation about a science article he posted to his Facebook wall, that probably seems normal.
If you meet a vague acquaintance at a party and strike up a conversation about the eco-lodge he chose for his honeymoon in the Maldives, he will likely back away from you slowly.
"And then," Ellison says, "you've violated the gray line of stalkerism."
Instagram's image-driven format gives you the eco-lodge, but not the science article.
And arguably, you've violated the gray line of stalkerism simply by looking at those photos in the first place, even if you don't reveal yourself in public as the sad lurker that you are.
Each time you swipe through more images of people's meals and soirees and renovation projects and holiday sunsets, you are potentially blurring the boundary between stranger-you-haven't-met and sleazy voyeur skulking around the cabana with an iPhone.
To be sure, daily acts of stalkerism are all but part of the social contract at this point. But stalkerism heavily diluted with links to articles, one-on-one messaging, Dr Oz ads, and second cousins who still play FarmVille will always seem more palatable than the uncut version.