What the WHO Actually Said
The International Agency for Research on Cancer (IARC), the cancer research arm of the World Health Organization, classifies night shift work as "probably carcinogenic to humans." This classification has been reviewed twice, most recently in 2019, and held both times.
The reason isn't the work itself. It's the circadian disruption that comes with light exposure during hours the body expects darkness. Researchers believe this disruption, repeated night after night, drives the increased cancer risk observed in:
- Breast cancer
- Prostate cancer
- Colon and rectal cancers
Most of us aren't night shift workers. But many of us are exposing ourselves to the same type of light, at the same problematic hours, inside our own homes.
Why Light at Night Is the Problem
Your body runs on a 24-hour internal clock that is set and reset by light. Blue-wavelength light — found in screens and most modern overhead lighting — is the most potent signal your body uses to stay awake and alert. When your brain detects it in the evening, it suppresses melatonin, the hormone responsible for sleep, immune repair and cellular recovery.
Research has linked chronic circadian disruption to:
- Mood disorders
- Metabolic dysfunction
- Obesity and diabetes
- Cardiovascular disease
- The cancer risk flagged by the IARC
The common thread across all of these is melatonin suppression and a body that never fully gets to do its overnight work.
A clinical study comparing blue and red light during evening hours found that after just two hours, melatonin levels were substantially lower under blue light than red light — which allowed natural recovery.
This Is a Home Environment Issue
Night shift workers have their circadian rhythms disrupted by their schedule. For most people, the disruption happens at home in the hours after darkness falls — in the lounge, in the bedroom, in the bathroom in the middle of the night.
Research comparing common bulb types found that white LED bulbs suppress melatonin more than five times more than orange-yellow alternatives. Every evening spent under bright overhead lighting or in front of screens is nudging your body clock in the wrong direction.
The good news is this is one of the most controllable risk factors in your home environment. You don't need to sit in the dark. You just need the right kind of light.
What to Change
Small adjustments your body responds to quickly:
- Switch bedroom and lounge bulbs to warm amber lighting above 580nm
- Dim down in the evening
- Reduce screen time, or use a blue light filter when screens are unavoidable
The Calm Lighting range is designed specifically for this. Zero blue light, warm amber at 610nm peak wavelength, 1600K colour temperature, Risk Group 0 certified.