Why Do Adolescents Stay Up So Late?

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No one needs a scientific study to know that when children reach adolescence, they begin to stay up later at night. Any group of parents—and the adolescents themselves—will readily confirm that as fact. But the reasons for staying up late are varied, and because insufficient sleep can lead to suboptimal school performance, poor emotion control, and poor health, considerable effort has been expended trying to isolate contributing factors that could inform interventions.

Two primary areas have been proposed as influencing late sleep: biological factors and social-behavioral factors. The primary biological explanations are based on numerous studies going back over 30 years finding that when puberty begins, secretion of melatonin from the pineal gland is delayed later in the evening. Melatonin is important in inducing sleepiness, so post-pubertal adolescents may have difficulty falling asleep early enough to get the amount of sleep they need. (See my previous post for information on taking melatonin tablets to help induce sleep.) Technically, the phenomenon of later sleep has been described as circadian phase delay, meaning that the 24-hour circadian cycle of alternating periods of wakefulness and alertness followed by sleepiness and sleep has moved an hour or two later. Relatedly, there are individual differences in predisposition to morningness (“larks”) and eveningness (“owls”). Adolescent circadian phase delay is the principal foundation upon which the movement to push school start times later is based. The assumption is that most adolescents cannot fall asleep early enough to get sufficient sleep before they must get up to attend early-starting schools. Dr. Mary Carskadon coined the term “perfect storm” to describe the confluence of biological, psychological, and social factors that cause insufficient adolescent sleep (Carskadon, 2011; Crowley, et al. 2018).

Besides the bioregulatory factors, a considerable number of non-physiological factors are involved in later sleep. All parents can confirm that as children get older, they wish to stay up later, often because it is seen as marker of privilege accompanying growing up. Activities such as watching TV, interacting with others on social media platforms, and playing computer-based or online games often extend late into the evening. Social structures, particularly school-related ones including homework assignments, school athletics practices and games, and other extracurricular activities such as choir and band can cause bedtimes to be later. These factors run headlong into the social structure that has been deemed most problematic by many: early school start times.

While biological and non-biological factors can operate independently, they can also interact. Exposure to artificial light from screens can delay melatonin release, so extended exposure to screens at night can add to natural phase delay. Limiting the duration of screen exposure, establishing good sleep hygiene practice (e.g. wind-down routines; keeping the bedroom cool and dark; avoiding evening exercise, caffeine, and snacks) have become intervention targets for better sleep.

In a study published recently in the journal Pediatrics (Jaakalillio et al. 2026), a group of scientists were able to estimate relative contributions of biological and behavioral impediments to sleep by studying a sample of late adolescents over many months who had delayed sleep phase. One finding was that delayed sleep phase was stable from adolescence into early adulthood; it typically got no better or worse. They measured several behavioral factors including compulsive gaming, self-control, fatigue, ADHD symptoms, conduct problems, depression, and alcohol use, and identified two groups with an increased risk for delayed sleep phase. Compulsive gaming characterized the first group and was the strongest factor overall. A second group was defined by a wide range of the other behavioral factors, with the authors concluding that poor self-regulation may underlie them. The biological measure was circadian thermoregulation; participants had their skin temperatures measured continuously in one-minute intervals over three days and nights. Because temperature drops after falling asleep, it is a good proxy for phase delay when paired with objective measurement of sleep with actigraphs. To the surprise of the researchers, though, the temperature measures did not relate to delayed sleep phase. They concluded that based on the factors they studied, behavioral, but not biological factors were associated with delayed sleep phase.

So turning back to the original question: Why do adolescents stay up so late at night? While bioregulatory factors certainly must play some part, this and other studies have led me to conclude that behavioral factors are likely more influential. The good news is that those factors appear to be more modifiable than biological factors. For example, many school districts in the U.S. and several countries (i.e. France; Spain) have taken measures to limit smartphone use and access to social media by adolescents. Parents can regulate, and adolescents can self-regulate, screen exposure and arousing social media and games. Better sleep hygiene can be practiced.

It will take more than delaying the start of school for adolescents to get sufficient sleep. Just as in the case of efforts to improve nutrition and health, we can make some structural changes (e.g. not having soda and snack machines in schools; nutritional labels on food), but without the self-discipline required, those changes will never be enough.

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