Light is the original language your body speaks. Long before clocks, calendars, or LEDs — sunlight and darkness told the human body when to wake up, when to eat, when to move, and when to sleep. And just because we traded caves for cozy homes (thank goodness, right?) doesn’t mean your body stopped relying on those same cues.

Circadian biology is simply the science of this: how your body uses light and darkness to set its internal timing. That timing system is called your circadian rhythm — a roughly 24-hour cycle that tells different systems in your body when to turn on and when to power down. It’s not something you have to think about or manage; it runs automatically in the background, responding to the environment around you.

And that’s the problem we’re facing. Your circadian rhythm is built to respond to the environment around you, but the modern environment looks nothing like the one it evolved in. Most of us spend our days indoors under artificial light, then flood our nights with more of it — barely seeing real daylight and almost never experiencing true darkness. Our biology hasn’t changed, but the world we live in has, and that mismatch is where so much confusion begins.

People love to argue that humans have already adapted to iPhones, LEDs, and being indoors all day. Sorry to say, that’s not how evolution works. Cultural evolution happens fast; we can change technology, lighting, and environments in a matter of months. Biological evolution happens slowly, through genetic change over tens of thousands of years — not over a few generations of smartphones. Our biology is still calibrated for the same light-and-dark signals it has always used, even though our environment has radically changed.

Your circadian rhythm doesn’t shift overnight. It drifts slowly as days, weeks, and months stack up with phone screens before sunlight, long indoor days, and bright light at night. We wake up to artificial light, spend most of the day inside, and stretch the evening with screens and overhead lighting. That slow accumulation is how rhythm slips — quietly, gradually, almost invisibly.

When circadian rhythm drifts, multiple systems start losing coordination. Sleep regulation, stress response, hormone signaling, metabolism, immune function, digestion, and inflammation all rely on circadian timing. Some women are more sensitive than others, but when that timing is off for long enough, the body stops communicating clearly with itself — and chronic issues start stacking instead of resolving.

When you zoom out and look at our health in modern culture, something doesn’t add up. We’ve never had more information, more tools, or more technology aimed at health — and we’ve never been sicker. Chronic illness, burnout, metabolic dysfunction, mood disorders, autoimmune conditions… they’re everywhere. Everyone knows someone who’s dealing with something. And it’s worth pausing to ask: is this really a coincidence? Or are we finally seeing what happens when ancient biology tries to live inside a very modern world?