What Sleep Hygiene Actually Means
The term sleep hygiene originated in clinical sleep medicine in the 1970s, where it referred to a set of behavioural recommendations for patients with insomnia. The original list was modest: maintain consistent sleep and wake times, avoid caffeine and alcohol close to bedtime, use the bed only for sleep, and keep the sleeping environment dark, cool, and quiet. These recommendations were based on clinical experience and plausible physiological reasoning.
Over the past decade, this modest clinical concept has expanded dramatically as sleep became a wellness priority. The list of recommended practices now extends to dozens of variables, many sold in some form — sleep supplements, tracking apps, specialised mattresses, blackout curtains. The line between evidence-based recommendation and commercial interest has become difficult to locate.
What the Evidence Supports
Sleep timing consistency is the best-supported behavioural intervention in the literature. Waking at the same time every day — including weekends — is robustly associated with better sleep quality across multiple study designs. The mechanism is well understood: the circadian clock entrains to regular light-dark cues, and irregular wake times create a form of chronic social jet lag that disrupts sleep architecture. This recommendation costs nothing and has no commercial beneficiary, which may partly explain why it receives less promotional attention than more marketable alternatives.
Light exposure matters, and the evidence here is reasonably strong. Morning bright light exposure advances the circadian phase and is associated with earlier, more consistent sleep onset. Evening bright light — particularly at wavelengths in the blue-green range — delays sleep onset and suppresses melatonin production. The practical implication is that spending time outdoors in morning light and dimming indoor environments in the evening should help most people sleep earlier and more easily.
Caffeine has a longer half-life than most people appreciate: approximately five to seven hours for most adults, with significant individual variation. Consuming caffeine after early afternoon is associated with delayed sleep onset and reduced slow-wave sleep duration in controlled studies, even when subjects report feeling unaffected.
Alcohol is frequently misunderstood as a sleep aid. It does reduce sleep onset latency. But it substantially disrupts the second half of the sleep cycle, reducing REM sleep and increasing arousals. The net effect on sleep quality is negative, and the effect on next-day cognitive function is measurably adverse even when the person reports feeling fine.
What Is Plausible but Uncertain
Bedroom temperature recommendations — typically in the range of 65 to 68 degrees Fahrenheit — have some empirical support and clear physiological rationale, but optimal temperature is highly individual and the evidence base is thinner than popular presentations suggest.
Exercise is associated with better sleep quality in observational data, but the relationship between timing of exercise and sleep is less clear than popular advice implies. The claim that vigorous evening exercise disrupts sleep appears to be weaker in the research literature than it was once thought.
What Lacks Good Evidence
Blue-light blocking glasses have a plausible mechanism but inconsistent empirical support. Systematic reviews have found mixed results, with some studies showing no benefit over ordinary glasses for sleep outcomes. The evidence does not clearly justify the commercial emphasis these products receive.
Sleep tracking consumer devices consistently show poor accuracy for sleep staging relative to clinical standards. Using them to monitor and optimise sleep can, in some individuals, create anxiety about sleep metrics that itself worsens sleep — a phenomenon clinicians have termed orthosomnia.
Many supplement categories marketed under wellness branding have minimal clinical evidence and are not well regulated. Melatonin has genuine evidence for certain applications — jet lag, circadian rhythm disorders — but is frequently used at doses far exceeding what the evidence supports.
The Practical Summary
The interventions with the strongest evidence are free: wake at the same time every day, get outdoor light in the morning, reduce bright light and caffeine in the evening, and be honest about alcohol's effects. The interventions with the most commercial momentum — tracking, supplements, specialised hardware — have considerably weaker evidence. Sleep genuinely matters, and the basic behavioural recommendations are worth taking seriously. The wellness industry's version of sleep hygiene is worth approaching more carefully.