Medicine & Health
What is The circadian rhythm?
The circadian rhythm is your body's roughly 24-hour internal clock that controls sleep, alertness, hormone release, and other functions. It is set mainly by light and dark, telling you when to feel awake during the day and sleepy at night.
See it, don’t just read it.
Watch a 2-minute lesson with voice + animation that explains the circadian rhythm.
Key things to understand
- 1A master clock in the brain (the suprachiasmatic nucleus) keeps the body on a ~24-hour cycle.
- 2Light is the strongest signal that resets it — bright morning light advances it, late-night light delays it.
- 3It governs the timing of hormones like melatonin (sleep) and cortisol (alertness).
- 4Disrupting it through jet lag, shift work, or late screens harms sleep, mood, and health.
- 5Keeping consistent light and sleep times keeps the rhythm well-aligned.
Frequently asked questions
- What controls the circadian rhythm?
- A cluster of brain cells acts as a master clock, synced mainly by light entering the eyes, which is why daylight and darkness shape your sleep timing.
- Why does jet lag happen?
- Crossing time zones puts your internal clock out of step with local light and time, so you feel sleepy or alert at the wrong hours until it resets.
- How do screens affect it?
- Blue-rich light at night signals 'daytime' to the clock, suppressing melatonin and making it harder to fall asleep.