Sleep — The brain's nightly reset

During deep sleep, the brain flushes out waste proteins through its cleaning system. This cycle only runs when you are unconscious. Skip it and the waste accumulates. Sleep is not rest. It is maintenance. The brain needs it the way a machine needs a shutdown for repairs.

• Teenagers need 8 to 10 hours of sleep. Most get less than 7.
• Screens before bed delay sleep because blue light blocks the hormone that signals tiredness (melatonin).