You can technically breathe under a blanket, but the environment rapidly shifts from breathable to dangerous. This situation involves simple physics regarding gas movement through fabric, quickly compounded by human physiology. While a temporary pocket of air exists, the continuous process of respiration fundamentally changes the composition of that air. Understanding the relationship between fabric permeability and the body’s need for fresh oxygen clarifies why this seemingly harmless habit can become hazardous.
The Physics of Air Exchange Through Fabric
No common fabric is truly airtight, which allows for initial breathing under a blanket. Textiles are composed of woven or compressed fibers, creating microscopic gaps between the threads that allow gases to pass through them. This process is known as diffusion, where gas molecules move from an area of higher concentration to an area of lower concentration.
Loosely woven materials, such as thin cotton sheets, have a high air permeability and permit a relatively quick exchange of gases with the surrounding room air. Denser or thicker blankets, like heavy wool or multiple layered comforters, possess greater vapor resistance, significantly slowing this gas exchange. While some diffusion occurs through the fabric itself, most fresh air initially enters the space through the blanket’s edges as the person moves.
The Physiological Danger of Oxygen Depletion
The danger arises from the mismatch between the rate of gas exchange and the body’s metabolic demand. Every breath you take consumes oxygen (\(\text{O}_2\)) and releases carbon dioxide (\(\text{CO}_2\)), rapidly depleting the available oxygen within the small, confined air volume under the blanket. The expelled air is trapped, leading to a process called rebreathing, where the same air is inhaled repeatedly.
This rebreathing causes an increase in the concentration of carbon dioxide (a state known as hypercapnia) and a corresponding drop in oxygen (hypoxia). For example, studies using infant models under bedding have recorded inspired \(\text{CO}_2\) levels reaching as high as 8.3%, which is significantly higher than the typical atmospheric level of less than 0.1%. High carbon dioxide levels are the body’s primary trigger for the urge to breathe, leading to faster, panicked respirations that only accelerate the buildup of \(\text{CO}_2\) and the depletion of \(\text{O}_2\).
A healthy adult will typically respond to this discomfort by instinctively moving or throwing off the blanket, which instantly breaks the seal and restores the air composition. However, if the blanket is dense and tightly sealed, or if the person is impaired by illness or deep sleep, the physiological response may be insufficient to avert the danger. The confined air pocket becomes a miniature atmosphere that the body’s constant metabolism quickly renders toxic.
Why Infants and Small Children Face Greater Risk
The physics and physiology of breathing under a blanket become significantly more hazardous when applied to infants and very small children. Their smaller lung capacity means the confined air volume under a blanket is proportionally smaller relative to their respiratory needs, accelerating the rate of oxygen depletion and carbon dioxide buildup. Infants also exhibit a higher metabolic rate relative to their body size, requiring them to consume oxygen and produce \(\text{CO}_2\) at a faster pace than an adult.
The most profound risk factor is the infant’s lack of motor control and muscle strength. Babies under one year old often cannot easily maneuver their head or use their limbs to push a blanket away if it covers their face, which greatly increases the risk of accidental suffocation. This inability to self-rescue is why soft bedding and loose blankets are strongly associated with accidental suffocation and strangulation in bed (ASSB). In fact, over 85% of all ASSB deaths occur between birth and six months of age, when mobility is most limited. Even a lightweight fabric can pose a serious threat if it is pressed against an infant’s nose and mouth, resulting in the rebreathing of expired air.