The belief that sleeping without a shirt can cause illness is common, often stemming from feeling unwell after cold exposure. This suggests that being cold directly triggers respiratory illnesses like the common cold or the flu. However, biology reveals that temperature alone is not the mechanism of infection. Understanding how viruses and the body’s natural defenses interact offers a clear scientific perspective on this concern.
Illness Requires a Pathogen
Illness, particularly an upper respiratory infection, is not caused by cold air or a lack of clothing. These infectious diseases require the presence of a specific pathogen, such as a virus or bacteria. The common cold is typically caused by hundreds of different viruses, including rhinoviruses and seasonal coronaviruses. The flu is specifically caused by the influenza virus.
These pathogens spread when tiny, virus-laden droplets are expelled into the air by an infected person through talking, coughing, or sneezing. Infection occurs when these airborne droplets are inhaled or when a person touches a contaminated surface and transfers the virus to their nose or mouth. Contracting an illness depends entirely on exposure to these infectious agents, not on the ambient temperature of the bedroom.
The Body’s Response to Cold During Sleep
While cold air cannot transmit a virus, exposure to a significantly cold environment while sleeping can affect the body’s physiological defenses against an already-present pathogen. The body must dedicate resources to thermoregulation, the process of maintaining its core temperature. This process becomes more demanding when the skin, especially the torso, is exposed to cold air without the insulation of a shirt or bedding.
To conserve heat, the body initiates peripheral vasoconstriction, where blood vessels near the skin’s surface narrow. This reflex response occurs in the mucosa of the nasal and upper airways, not just the extremities. This constriction reduces the flow of warm blood to the respiratory tract, locally cooling the nasal passage.
This cooling can temporarily impair the local immune response, which functions as the first line of defense in the nose. Research indicates that even a small drop in nasal tissue temperature can significantly reduce the release and efficacy of anti-viral extracellular vesicles. These vesicles are protective particles that neutralize viruses and protect uninfected cells. A reduction in this defense allows viral replication to proceed more efficiently, potentially converting an asymptomatic infection into a symptomatic cold.
Ideal Conditions for Restorative Sleep
The best way to support immune function during sleep is by maintaining a comfortable thermal environment that promotes restorative rest. The body naturally lowers its core temperature when falling asleep, and a cooler room facilitates this necessary drop. Most sleep experts suggest an optimal ambient temperature range for adults is between 60 and 67 degrees Fahrenheit (15.5 and 19.5 degrees Celsius).
Sleeping in a room that is too cold forces the body to expend energy to generate heat, leading to discomfort and fragmented sleep. Disrupted sleep interferes with the body’s ability to allocate energy and resources to immune system functions. Conversely, a room that is too warm can lead to night sweats and awakenings, preventing the deepest, most restorative stages of sleep.
Choosing to sleep without a shirt can be part of optimal thermal regulation if the room temperature is managed appropriately and sufficient bedding is available. The key is to avoid sustained cold exposure that forces the body into constant thermoregulatory stress. Maintaining a temperature within the recommended range helps ensure the body’s resources are directed toward rest and immune surveillance, regardless of clothing choice.