Teen Instagram star Essena O'Neill amassed a large following just based on photos of her life. Recently, after reaching nearly a million followers, the 19-year-old decided to tell her fans the secret behind her success: Self-doubt and addiction to her screen.

So, just like most people eventually do with a bad habit, she decided to kick it to the curb.

"Social media, especially how I used it, isn't real," she said in a video announcing her decision. "It's contrived images and edited clips ranked against each other. It's a system based on social approval, likes, validation in views, success in followers. It's perfectly orchestrated self absorbed judgement. I was consumed by it."

She has since edited the original captions on her Instagram photos, explaining the real work that went behind seemingly "candid" shots ("A 15-year-old girl that calorie restricts and excessively exercises is not goals," one edited photo reads). She also deleted her YouTube account and started a website dedicated to mindful use of social media.

O'Neill's story is certainly not the first example of the false illusions and negative feelings caused by social media, but it does highlight a growing, under-addressed health problem for young people. An extensive new survey from Common Sense Media found that teens spend nearly nine hours a day using their devices.

Technology certainly has the power to inspire positive change, but overindulgence can have dangerous consequences. Here are just a few ways excessive screen use can take a toll on teens' well-being -- and a few tips to keep in mind:

Too much tech can lead to weight gain.

Technology has a way of usurping physical activity, and it may show in teens' health. One study found that increased screen time was associated with larger waistlines in adolescents, Scientific American reported. Swapping social media scrolling with some adventures outdoors can improve every aspect of someone's health -- and it feels way better than a Facebook "like."

Excessive social media use is a sign of loneliness.

Social media has a way of prompting FOMO in real time, simply with a scroll through a newsfeed. A 2014 study found that excessive Facebook use may be a sign of loneliness. Not only that, research shows the popular social media site can make people feel sadder and less satisfied with their life.

It also leads to social comparison.

Research shows the reason why people feel so bad when they use social media is because of a subconscious process called social comparison, or stacking up their own life against someone else's. This can result in the user feeling less satisfied with their own life. A friendly, gentle reminder for anyone who thinks someone's life is better than their own: An Instagram filter often acts as a rose-colored lens. Social media is often used as a highlight reel, not an accurate portrayal of someone's reality.

Screens make multitasking super tempting.

The recent Common Sense Media survey also reveals a growing trend with multitasking, saying many young adults felt comfortable engaging with multiple tech mediums while doing their homework. Studies show multitasking can ruin a person's productivity on tasks in the long run. As tempting as those puppy videos in the background might be, it may be wiser to compartmentalize the two activities.

They may also hurt teens' grades.

Limiting excessive tech use may also boost test scores. A recent study from the London School of Economics revealed that students saw remarkable improvement in test gradesafter smartphones were banned from the classroom, CNN reported. Knowledge is power.

Overall, excessive online media can jeopardize teens' health.

Smartphones can cause the perfect storm for health implications. Research shows that adolescents' media consumption -- in addition to lack of sleep and physical activity -- puts them in jeopardy for psychiatric conditions just as much as their high-risk peers who abuse alcohol, skip school or engage in other potentially dangerous behaviors. Mindful use of technology is possible, and probably the most effective antidote when it comes to screens' negative effect on well-being (check out these suggestions for how to have a healthier smartphone relationship). Just like with most things, moderation is essential. The body and brain depend on it.