Many people assume that cold temperatures effectively eliminate viruses. However, cold generally does not “kill” viruses in the same way heat can destroy them. The reality is more nuanced. This article clarifies the actual effects of cold on viruses, explaining how they manage to persist and what this means for public health.
How Cold Temperatures Affect Viruses
Cold temperatures typically inactivate or preserve viruses rather than destroying them. Freezing or refrigeration significantly slows viral activity, but it does not inherently break down their fundamental structure. Storing viruses at extremely low temperatures, such as -80°C, is a common laboratory practice for long-term preservation. This highlights that cold largely maintains viral integrity.
The distinction between “killing” and “inactivating” is important when discussing viruses. Instead, inactivation refers to rendering a virus unable to replicate or infect a host cell. Unlike living organisms, viruses do not have metabolic processes that cold temperatures could halt. While extreme cold can sometimes cause damage, many viruses are remarkably resilient.
Mechanisms of Viral Survival in Cold
Viruses are not considered living organisms, which is a key factor in their ability to survive cold. They do not carry out metabolic processes or reproduce independently; instead, they hijack the machinery of host cells to make copies of themselves. This lack of biological activity means cold temperatures do not directly affect a virus’s life functions.
A virus’s simple structure further contributes to its resilience in cold environments. Viruses consist primarily of genetic material (DNA or RNA) encased within a protective protein shell called a capsid. Some viruses also have an outer lipid envelope. This robust casing shields the genetic material from environmental stressors, including low temperatures.
For instance, the influenza virus has a lipid membrane that can solidify into a gel at temperatures near or below freezing, which helps protect the virus as it transmits. Noroviruses are particularly resistant, capable of surviving freezing temperatures and remaining infectious on surfaces for days or even weeks.
Real-World Impact of Viral Persistence in Cold Environments
The persistence of viruses in cold conditions has tangible implications for public health. The seasonal patterns of illnesses like influenza are partly explained by the fact that the virus survives longer in colder, drier air. This enhanced stability, combined with people spending more time indoors, contributes to increased spread during winter months. Additionally, cold temperatures can weaken the immune response in the nasal cavity, making individuals more susceptible to infection.
Understanding viral survival in cold is also important for food safety. Norovirus can contaminate food and surfaces, and refrigeration or freezing does not eliminate it. It can survive from freezing temperatures up to 145 degrees Fahrenheit, persisting on hands for hours and on solid surfaces for days. This emphasizes the necessity of proper food handling and hygiene practices, including thorough cooking and diligent handwashing, even for refrigerated or frozen items, to prevent the transmission of these resilient pathogens.