Teenagers often shift to later bedtimes, a pattern noticed across many countries.

The longer version

Around puberty, the internal clock tends to drift later, so sleepiness arrives later in the evening and waking early becomes harder. The shift has been measured both with questionnaires and with physiological markers such as melatonin timing. It appears in many countries and is not explained by homework or screen use alone.

Because school schedules usually stay early, the mismatch is common and is reported across many countries. The pattern is not simply disobedience or laziness; it reflects a real change in timing that partly reverses in the early twenties. Later school start times have been trialled in several places, and the results have generally shown longer sleep for students.

Where this entry sits

This collection gathers curious details about sleeping and dreaming, from nightly brain stages and body clocks to naps, yawns and unusual animal habits. It also covers how bedtime customs have changed across centuries, without offering any advice. The full list sits on the Sleep and Dreams page, where every entry is listed in order.