Advice about sleep concentrates on what individuals do, and several substantial determinants sit outside individual control entirely.

Noise

Traffic, aircraft and neighbour noise fragment sleep measurably, including where the sleeper does not wake.

Which has been studied extensively, with health effects attributed to night noise exposure in large populations.

Exposure correlates with housing cost, which means quieter sleep is effectively purchased.

Guideline limits for night noise exist and are exceeded for substantial populations in most countries that measure it.

Light

Street lighting, illuminated signage and light from neighbouring buildings all reach bedrooms.

Which affects circadian regulation and sleep quality.

Blackout curtains address it and are a cost, and the underlying exposure is a planning and lighting design question.

Temperature

Bedroom temperature affects sleep substantially, and controlling it depends on building quality and on affordable heating and cooling.

Which means poorly insulated housing produces both cold and overheating problems.

Overheating in bedrooms during heatwaves has measurable effects on sleep and on mortality.

Housing quality

Damp, mould, overcrowding and insecurity all affect sleep.

Which are addressable through housing policy and standards rather than through individual behaviour.

Overcrowding specifically, where people share sleeping space, makes conventional sleep advice largely inapplicable.

Shift work

Requires sleeping against the circadian rhythm.

Which produces chronic misalignment with associations across a range of health outcomes in occupational research.

Mitigation through shift scheduling, rotation direction, light management and rest provision exists and is inconsistently implemented.

Caring responsibilities

Night waking to care for a child, a relative or a person with a condition.

Which is a substantial cause of chronic sleep restriction for a large population, and no sleep hygiene advice addresses it.

Respite provision is the intervention, and availability is limited in most places.

Financial and job insecurity

Worry disrupts sleep, and financial insecurity is among the most consistently reported causes.

Which means addressing the insecurity affects sleep more than any behavioural change would.

Free debt advice services are the practical route for the financial component and are consistently underused.

What follows

Individual sleep advice is useful within the constraints a person actually faces.

Which means delivering it to someone whose sleep is disrupted by night shifts, a noisy street and a young child is not helpful and can add a sense of failure.

Recognising which constraints are structural is what makes the remaining advice usable.

Persistent sleep problems warrant medical assessment, since treatable conditions including sleep apnoea and insomnia are common and specific treatments exist.

Air quality

Indoor and outdoor air quality affects respiratory symptoms and, through them, sleep.

Which is relevant near busy roads and in homes with damp or poor ventilation.

Ventilation improves indoor air and, near a noisy road, conflicts directly with the need to keep windows closed for quiet.

Medication

Several common medications affect sleep, either directly or through side effects.

Which is worth reviewing with a doctor or pharmacist where sleep problems began around a medication change.

Timing of doses can matter, and adjusting it is sometimes sufficient.

Untreated conditions

Sleep apnoea, restless legs, chronic pain and several others disrupt sleep and have specific treatments.

Which means treating the condition, rather than the sleep, is the effective route.

Sleep apnoea in particular is substantially underdiagnosed and has effective treatment, and loud snoring with pauses is the recognised indicator.

Light exposure during the day

Daytime light exposure supports circadian regulation, and indoor workplaces provide far less than outdoor conditions.

Which is a constraint of the work rather than a choice, and time outdoors during daylight addresses it partially.

The effect is larger in winter at higher latitudes where daylight hours coincide with working hours entirely.

What individual advice can still do

Consistent timing, a wind-down period and limiting caffeine late in the day are supported and are within reach for most people.

Which is worth doing where the structural constraints permit it.

Cognitive behavioural therapy for insomnia has stronger evidence than any other approach and is recommended as first-line treatment ahead of medication.

Screens

Commonly blamed and probably less important than the content and timing of what is being done on them.

Which is reflected in research finding effects of engagement and arousal larger than effects of light emission alone.

Work email in the evening keeps people awake for reasons that have little to do with the display.

Alcohol

Reduces time to fall asleep and degrades sleep quality in the second half of the night.

Which is a consistent finding and runs directly against how it is commonly used.

The effect on sleep architecture is measurable at fairly modest intakes.

Chronotype

Individual timing preference has a substantial genetic component and is not a habit.

Which means later chronotypes face a persistent mismatch with conventional working hours.

Flexible start times address it directly where the work allows, and the effect on sleep is larger than most behavioural advice achieves.