Why do we need sleep?

Sleep is not idleness; it is active maintenance. At least three major jobs run during it — clearing waste from the brain, consolidating memory, and repairing and growing tissue.

Metabolic waste accumulates in the brain during the day. In sleep the spaces between brain cells widen and a flow of fluid flushes that waste out — a clearing process that does not run as efficiently while you are awake.

The memory side matters just as much. What you learned during the day moves from temporary into long-term storage while you sleep. That is why studying through the night before an exam often backfires — more is covered, less is retained.

Sustained short sleep erodes attention, judgement and immune function. Teenagers need more of it than adults, because their brains and bodies are still developing.

How much sleep you need varies with age, and that is biology rather than habit. In adolescence the body clock naturally shifts later — so falling asleep late and struggling to wake early is not laziness. Keeping consistent hours and avoiding bright screens before bed both help that clock settle.