What does less screen time do for your body?

In a randomized trial (BMC Medicine 2025), three weeks with at most two hours of smartphone time per day improved stress, sleep quality, depressive symptoms and wellbeing. An experimental study (2018) linked five days off Facebook with lower cortisol.

Does less phone time lower the stress hormone cortisol?

An experimental study from 2018 found lower salivary cortisol after five days without Facebook. The study is small, so: linked with, not proven cause.

← Blog Health·5 min read·July 2026

What less screen time does to your body

Less screen time is linked in studies with less stress, better sleep and higher wellbeing, and early experimental work even shows effects on the stress hormone cortisol. Here is what the research really supports, what remains open, and why we phrase it carefully.

The strongest card: a real randomized trial

In 2025, BMC Medicine published a randomized controlled trial with 111 students: for three weeks, the intervention group used their smartphone for at most two hours a day. The result: less stress, fewer depressive symptoms, better sleep quality and higher wellbeing, with small to medium effect sizes. That is not a survey correlation but a controlled experiment, which is exactly why it is the most important study on this list.

Cortisol: the body relaxes measurably

Back in 2018, an experimental study in The Journal of Social Psychology showed: in people who gave up Facebook for five days, the stress hormone cortisol in saliva dropped. The interesting part: participants did not immediately feel better, yet their bodies responded anyway. The study is small and self-selected, so we say: linked with, not caused by.

Sleep: the best documented effect

Screen use in bed is consistently linked in meta-analyses with falling asleep later and sleeping less. In the German JIM study 2025, about 30 percent of teenagers say they are tired in the morning because they were on their phone at night. And sleep is the foundation of almost everything else: mood, focus, immune system.

Attention: two weeks are enough for a difference

In the randomized Castelo study (PNAS Nexus 2025), two weeks without mobile internet improved subjective wellbeing, mental health or objectively measured sustained attention in 90.7 percent of participants in at least one of the three areas.

What this means for you

You do not need a radical detox. The studies suggest that reliably protected windows, a quiet evening, a focused morning, a bedroom without a feed, already change something measurable. That is exactly what the ctrl key is built for: not more discipline, but less friction for the good hours. All numbers with sources live in our research library.