Buy a sleep mask because you want your room dark and cannot make it dark any other way. That is a good enough reason, and it is a claim nobody has to substantiate — a mask blocks light, demonstrably, in the way a curtain does. The trouble starts when the marketing goes further, and most of it does. This page walks through what the evidence actually supports, including the inconvenient parts.
Do sleep masks improve sleep?
In hospitals, quite possibly. At home, the evidence does not currently show it. Those are two different findings and they get merged constantly, including by people who should know better.
What the hospital research shows
A 2023 network meta-analysis pooled 31 randomised trials covering 2,036 critically ill patients, comparing eleven interventions — eye masks, earplugs, music, aromatherapy, meditation, routine care and others. Eye masks ranked at the top of the ordering, with masks and earplugs together close behind.2
Read the small print, though. Only five of the thirty-one trials were rated low risk of bias. Heterogeneity between studies was 98.2%, which is close to total inconsistency. No formal grading of evidence certainty was carried out. And every outcome was a self-reported questionnaire — no polysomnography, no actigraphy — in trials where nobody could be blinded to whether they were wearing a mask. Ranking first in a network like that is a weak signal, not a strong one.
There is also the setting. An ICU has 24-hour lighting, alarms, overnight procedures, pain and often delirium. A mask there is removing a genuinely pathological stressor. Your bedroom is not an ICU, and there is no basis for transferring the size of that effect to it.
What happens outside hospital
Here is the part that most sleep-mask marketing skips. The one properly conducted study of healthy adults sleeping in their own beds — 89 people in the first experiment, 33 in a second with EEG monitoring — found no difference in self-reported sleep quality, no difference in sleep duration, and no difference in sleep architecture on objective measurement.3 Slow-wave sleep did not increase.
That study is the one usually cited to prove masks work. It found something else, which we come to next. On sleep itself, it found nothing changed — and there are no adequately powered home-based data on sleep-onset latency, total sleep time or night-time awakenings for eye masks in healthy sleepers. The evidence base is essentially hospital-only.
What about the memory and alertness study?
It exists, it is interesting, and it is contested in print. You should have all three of those facts before anyone sells you anything on the back of it.
The study had participants aged 18–35 wear an eye mask for a week, then spend a week with light unblocked, and tested them at the end of each. It reported small improvements in word learning and reaction time after the mask week.3 Note the effects were small to begin with.
A reanalysis published in the same journal then refitted the models with the random effects the original had omitted. The primary learning outcome became non-significant, with a confidence interval crossing zero; the reaction-time result survived only marginally. In practical terms the author put the effect at zero to two extra words out of eighty, or a tenth of a millisecond to twelve milliseconds.4 The original authors published a reply,5 so this is an open argument rather than a settled one.
What that adds up to: a single-lab finding, small even before reanalysis, whose primary outcome does not survive a proper model. We are not going to tell you a mask improves your memory, and the studies were run with plain masks in any case — nothing about our design has been tested for any cognitive effect, and nor has anyone else's.
Do they do anything for your body clock?
No — and the claim is close to backwards, which is worth understanding because you will see it everywhere.
Your circadian clock is set by light reaching the retina while you are awake, following a predictable pattern: light in the early morning pulls the clock earlier, light in the evening pushes it later. Morning light is the dominant signal. A mask worn after lights-out delivers no timing signal at all, and by blocking dawn light it removes one.
There is a narrow version that could hold: light does penetrate closed eyelids, and enough of it can shift melatonin timing.10 So in principle a mask could prevent an unwanted shift from light hitting closed eyes mid-sleep. But nobody has measured melatonin onset or body-temperature phase with and without an eye mask. Not one study. And the most-cited experiment on room light during sleep found melatonin unchanged.6
The distinction worth holding onto: a mask shields your eyes during the sleep window. It does not regulate, reset or stabilise anything, because regulation needs a timed light signal and a mask's entire function is the absence of one. If your body clock is the problem, get morning light. That is where the evidence is.
Bedroom light and long-term health
Before the detail: none of the research below used eye masks, and a mask would not have changed a single measurement in it. We are including it because it is the honest reason researchers care about darkness at night, not as an argument for buying anything.
Large observational studies have found associations between light exposure at night and metabolic conditions. The strongest is a UK Biobank analysis of around 13 million hours of wrist light-sensor data from 84,790 people followed for nearly eight years, which found a clean dose–response relationship with incident type 2 diabetes, independent of genetic risk.7 Smaller studies in older adults point the same way.89
Three caveats decide what you can do with that. These are associations, not demonstrated cause — no trial has shown that reducing light at night lowers anyone's diabetes risk. The measurements were ambient room light or wrist-worn sensors, which do not record what reaches your eyes. And confounding by shift work, sleep duration and body weight is live in all of them.
So it is a real and active research question about light in bedrooms. It is not a health claim about a mask, and we are not making one.
So what is a sleep mask actually for?
Now that everything unsupportable is out of the way, the honest case is short and it holds up without a single citation:
- Darkness you can carry. Blackout blinds work brilliantly and stay in one building. A mask works in a hotel with a gap in the curtains, on a night train, in a spare room, on a long-haul flight.
- Darkness that does not need permission. If you share a room with someone who reads late, or you sleep during the day after a shift, the light is not yours to switch off.
- It costs very little and nothing is at stake. Compared to new windows, a mask is a rounding error, and if it does not suit you, you have lost an evening finding out.
- Nothing to charge, pair or update. It works in a room with no plug by the bed, and there is no volume setting to get wrong.
- Summer mornings. If you wake at 4.30am from June to August, this is a solved problem and a mask is the solution.
None of that requires the research above to have gone our way. It is why we think the honest version of this page sells the product better than the version it replaces.
About the Shloof design
A description, not a claim. The mask uses a fabric-covered band that follows the contours of the head, so the seal comes from the shape rather than from pressure across the eyes — there is room for your eyelids to move, which is the usual reason people give up on masks. It wraps rather than straps, covering the ears and cushioning the head, and it is built to breathe when the room is warm without going thin when it is cold.
The sleeve takes interchangeable accessories, so one mask can be set up for light alone or for light and sound together depending on where you are sleeping. It is designed to work packed in a bag as well as on a bedside table.
If noise is the bigger half of your problem, we have written separately about how noise is measured and what actually reduces it, and about what sleep does for you and how much you need.
How to choose one
- Test it lying down, in your actual sleeping position. A mask that seals sitting up may gape when your face is against a pillow.
- Check for pressure on the eyelids. This is the single most common reason masks end up in a drawer. Your eyes move during REM; a mask that presses on them will wake you.
- Look for light leaking at the nose. The bridge of the nose is where most designs fail, and it is exactly where morning light comes in.
- Make sure it washes. You are wearing it against your face for a third of your life.
- Give it a fortnight. Most people find anything on their face odd for the first few nights. If it is still annoying after two weeks, it is the wrong mask, not the wrong idea.
General information, not medical advice. If poor sleep is persistent, speak to your GP — for insomnia, the first-line treatment in the UK is cognitive behavioural therapy, not a product.
References
- Atherton, A. (2024, January 24). New sleep mask benefit unlocked: Improved brain function. Sleep Foundation. Read more. An earlier version of this page drew on this article; it is credited here as its source.
- Huang, D., Li, Y., Ye, J., Liu, C., Shen, D., & Lv, Y. (2023). Different nursing interventions on sleep quality among critically ill patients: A systematic review and network meta-analysis. Medicine, 102(52), e36298. Read more.
- Greco, V., Bergamo, D., Cuoccio, P., Konkoly, K. R., Muñoz Lombardo, K., & Lewis, P. A. (2023). Wearing an eye mask during overnight sleep improves episodic learning and alertness. Sleep, 46(3), zsac305. Read more.
- Rhodes, S. (2023). No clear or consistent evidence that wearing an eye mask leads to meaningful improvement in learning and alertness: A reanalysis of Greco et al. (2023). Sleep, 46(8), zsad105. Read more.
- Lewis, P. A., et al. (2023). Response to Rhodes. Sleep, 46(8), zsad148. Read more.
- Mason, I. C., Grimaldi, D., Reid, K. J., Warlick, C. D., Malkani, R. G., Abbott, S. M., & Zee, P. C. (2022). Light exposure during sleep impairs cardiometabolic function. Proceedings of the National Academy of Sciences, 119(12), e2113290119. Read more.
- Windred, D. P., Burns, A. C., Rutter, M. K., et al. (2024). Personal light exposure patterns and incidence of type 2 diabetes. The Lancet Regional Health – Europe, 42, 100943. Read more.
- Kim, M., Vu, T.-H., Maas, M. B., et al. (2023). Light at night in older age is associated with obesity, diabetes, and hypertension. Sleep, 46(3), zsac130. Read more.
- Obayashi, K., Yamagami, Y., Kurumatani, N., & Saeki, K. (2020). Bedroom lighting environment and incident diabetes mellitus: A longitudinal study of the HEIJO-KYO cohort. Sleep Medicine, 65, 1–3. Read more.
- Figueiro, M. G., & Rea, M. S. (2012). Preliminary evidence that light through the eyelids can suppress melatonin and phase shift dim light melatonin onset. BMC Research Notes, 5, 221. Read more.