According to g9sleeptight.com (and many other websites), sleeping with the head under the blanket

  • increases the risk of suffocation
  • can trigger sleep apnea
  • can cause brain damage stating "some studies indicate that up to 23% of individuals that sleep with their head below the sheets develop dementia"

Are these negative health impact of sleeping with the head under the blanket valid?

In particular, they claim "some studies" show that 23% of the people that sleep with the head under the blanket develop dementia (a statistic which means nothing without knowing what the percentage is in the people who sleep with the head out of the blanket). Did they make this number up or does it really come from empirical observation?

  • 1
    I was not sure if I had to limit my question to the claim about dementia alone. If you think, I should, please let me know and I will narrow the scope of my question down.
    – Remi.b
    Nov 28, 2017 at 5:34
  • 2
    As a general claim that "sleeping with the head under blankets causes health problems" I don't see the question being too broad, especially as three specific claims are provided, one of which is numerical and can be evaluated or looked up.
    – Nij
    Nov 28, 2017 at 10:20
  • 1
    I think the dementia question is quite different to the suffocation/apnea question. BTW prevalence of dementia depends on the age group you are talking about. General level is much lower for aged 60+, but much higher for aged 85+.
    – Oddthinking
    Nov 28, 2017 at 14:49
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    I take that back. Sleep apnea is linked to dementia, so perhaps they will be answered together.
    – Oddthinking
    Nov 28, 2017 at 14:52
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    @DanielRHicks If you just mean there is a potential confounding variable in the relationship between covering its head and dementia in eventual studies we could find, then I could agree. However, your comment might sound a little judgmental suggesting that there is necessarily a root problem to treat. Personally, I got interested in the question 1) because I often cover my head when I sleep outside while travelling (for the heat and absence of light) and 2) because when my wife and I invite the dog to sleep in our bed (happens about twice a week), he typically goes under the blanket.
    – Remi.b
    Nov 28, 2017 at 23:29

1 Answer 1


Assuming that sleeping with head under blanket increases CO2 levels, you can find plenty of studies on the more immediate effects of the latter, e.g.,

It has been shown that when bedroom air quality was improved in these experiments:

  • Subjects reported that the bedroom air was fresher.
  • Sleep quality improved.
  • Responses on the Groningen Sleep Quality scale improved.
  • Subjects felt better next day, less sleepy, and more able to concentrate.
  • Subjects' performance of a test of logical thinking improved.

As for sleep apnea, the longer-term associations between that and brain function have been studies (because it occurs naturally)

people with sleep apnea tended to develop memory problems and other signs of mild cognitive impairment (MCI)

As to directly answer your question, I think I know where the 23% came from:

What percentage of dementia overall could be attributed to head covering while sleeping? Considering those 60 years of age and older, comparing those who do not practice head covering and were at a middle or late stage of dementia (assuming these to have suffered dementia due to causes other than head covering) to those that practice any level of head covering and who were at a middle or late stage of dementia (causes other than head covering plus head covering), 23% were attributed solely to head covering. If we consider that this percentage could also be attributed to all levels or stages of dementia, we can assume that 23% of all cases of dementia are due to head covering while sleeping.

It's a self-published (thus not peer-reviewed) survey conducted by an elementary school teacher.

There's not much in the way of direct studies of the effects of blankets on even breathing, let alone longer-term effects... I found one pretty old (1972) and small-scale experimental study, probably conducted at a US army facility given the author's affiliation, which was published in JAMA (as very, very short note):

Methods.— The effect on the inspired oxygen and carbon dioxide concentrations was studied in five healthy men, 25 to 30 years old. Each volunteer rested quietly though not sleeping, in the left lateral decubitus position on a sheet-covered mattress. The head was covered for ten minutes by one sheet and one standard AUS blanket weighing 3 to 4 lb and then by one sheet and two blankets for an additional ten minutes. All coverings were tucked under the mattress except the headward edge which was laid flat on the top surface. Samples of air from under the covers were obtained at one, five, and ten minutes from a catheter placed adjacent to the mouth of the subject. The subject held his breath at the end of inspiration during the sampling interval. The barometric pressures varied between 757 and 759 mm Hg during the study.

Results.— Before covering the head, the oxygen concentration was 20.7% to 20.9%, and the carbon dioxide concentration was 0.4% to 0.5%. Upon covering the head with one or two blankets, the mean oxygen percentage rapidly decreased to 18% to 19% and the mean carbon dioxide rose to 1% to 2% within one minute and thereafter remained stable. Hypoxia as low as 16.5% oxygen, and hypercapnia as high as 4.1% carbon dioxide was obtained beneath the covering of two blankets.

To ascertain the frequency of this habit, 100 healthy individuals, 41 women and 59 men with a mean age of 32 years were asked whether they cover their heads before falling asleep. The survey revealed that 11 of them, two women and nine men, with a mean age of 29 years, covered their heads with one or more blankets before going to sleep. Most of them (7 of 11) covered their heads every night or every other night.

The author went on say that the changes were insignificant in healthy individuals, but relevant in those with "borderline compensated oxygen delivery system such as congestive heart failure" and that "hypercapnia may be harmful in that carbon dioxide may induce cardiac arrhythmias or depress myocardial contractility in predisposed individuals."

Also, I looked for studies on whether hypercapnia can cause sleep apnea, but I wasn't able to find that. What I did find was that some but not all people with obstructive sleep apnea also exhibit daytime hypercapnia.


In sleep apnea patients, the chronic hypercapnia develops adaptive mechanisms to diminish the hypoxic negative effects.[citation] Plausible explanations to this effect are hyperventilation, increases in the ventilation–perfusion relationship, improvements in tissue oxygen delivery changing the hemoglobin oxygen affinity, increases in CBF due to vasodilation, and so forth. Brain oxygenation can improve when hypercapnia and hypoxemia are combined; nevertheless, this is a controversial topic.[citations]

And regarding ASSB (accidental suffcation and strangulation in bed), it's generally considered a risk factor for infants, but dimishes drasticly after 6 months of life.

So I think that discounting the self-published survey, most of the inferences in the original question here can be chalked up to jumping to conclusions from seemingly plausible mechanisms, but not supported by available evidence.

  • The sleeping condition where I find myself covering my head (though not my face or at least not nose + mouth) is winter camping (my sleeping bag is meant to be used with its "hood"). It is associated with lots of fresh air ;-) Nov 29, 2017 at 16:49

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