The habit of pulling a blanket completely over the head is a common practice, often driven by the desire for darkness, noise reduction, and a sense of cozy security. This action creates a small, private microclimate that shields the sleeper from external stimuli. While offering comfort, this practice introduces specific physiological changes that raise questions about its impact on restorative sleep. Understanding the shifts in the air environment and the body’s response helps determine if this sleeping style is ultimately harmful.
Changes in Air Composition Under the Covers
Enclosing the head beneath a blanket immediately alters the air composition surrounding the face. With every breath, the body consumes oxygen and exhales carbon dioxide, leading to rebreathing. This process causes the concentration of carbon dioxide (CO2) to rise and the percentage of oxygen (O2) to decrease within the enclosed area.
In a normal room, oxygen is about 20.9% and carbon dioxide is roughly 0.4%. Studies show that covering the head can cause oxygen concentration to drop to 16.5%, while CO2 levels can spike to 1-4.1% within minutes. This rise in CO2 creates mild hypercapnia, which the brain detects. The brain responds by increasing the breathing rate to clear the excess gas. This compensatory mechanism can lead to fragmented sleep or cause the sleeper to wake up feeling groggy or with a mild headache.
Impact on Thermoregulation and Sleep Quality
Using a blanket to cover the head interferes with the body’s natural thermoregulation process during sleep. The head is a highly vascular area and serves as a major site for heat dissipation, allowing the body to reduce its core temperature. This core temperature drop is an important signal that helps initiate and maintain sleep.
Covering the head traps the heat and moisture released through breathing and skin evaporation, creating a warm, humid microclimate. This artificial insulation prevents the normal heat loss required for restorative sleep, potentially leading to hyperthermia. A rise in core body temperature negatively impacts sleep architecture, often increasing wakefulness and reducing time spent in deep (slow-wave) and Rapid Eye Movement (REM) sleep. Trapped moisture can also cause increased sweating near the face, which may lead to skin irritation or discomfort, further disrupting sleep.
Differentiating Risk by Age and Blanket Type
The risk associated with this habit is not uniform and depends on the individual’s characteristics and the materials used. For healthy adults, protective reflexes, such as the urge to adjust position or move the blanket, typically prevent serious harm from slight CO2 buildup. However, individuals with existing respiratory conditions, such as asthma or Chronic Obstructive Pulmonary Disease (COPD), or cardiovascular issues like congestive heart failure, are more susceptible to the negative effects of minor O2 depletion and CO2 accumulation.
The danger is more acute for vulnerable populations, particularly infants and young children. Infants lack the motor skills and muscle strength to move a blanket from their face if breathing is compromised. They also cannot regulate their body temperature as efficiently as adults, making overheating a substantial risk factor. This combination of rebreathing risk and hyperthermia is a concern related to Sudden Infant Death Syndrome (SIDS). Medical guidelines strongly advise against any head covering or loose bedding in a crib. The breathability of the blanket material also plays a role, as a heavy, dense synthetic comforter restricts air exchange more severely than a thin, loosely woven cotton sheet.
Safer Alternatives for Light and Noise Control
For those who cover their heads primarily to achieve a dark and quiet sleeping environment, several alternatives offer comfort without the associated physiological risks. To manage light, a contoured sleep mask blocks visual stimuli while leaving the face exposed for unrestricted airflow. Installing blackout curtains also creates a pitch-black room environment that supports the natural production of melatonin.
To address noise, earplugs or specialized sleep headphones can muffle external sounds. Using a white noise machine or app provides a consistent, masking sound that helps prevent sudden environmental noises from causing arousals. Implementing these changes allows the sleeper to enjoy darkness and quiet while ensuring optimal air quality and thermoregulation.