The question of whether cold temperatures destroy SARS-CoV-2, the virus that causes COVID-19, is common, especially since respiratory illnesses spike in winter. The assumption that cold kills germs is largely incorrect for this specific pathogen. Far from being destroyed, the virus is highly stable in cool and cold conditions. The cold acts as a preservative, significantly extending the time infectious particles remain viable on surfaces and in the air.
Virus Viability: How Temperature Affects Survival
SARS-CoV-2 is an enveloped virus, meaning its genetic material is encased in a protective layer of lipids acquired from the host cell. This lipid envelope is the virus’s main structural vulnerability, easily dissolved by soap, alcohol, and high heat. When the surrounding temperature is elevated, the envelope components become less stable, causing the virus to degrade quickly and inactivating it.
At non-freezing cold temperatures, such as those found in a refrigerator (around 39°F or 4°C), the lipid envelope remains rigid and intact. Laboratory studies show the virus can survive for over two weeks at refrigeration temperatures. In contrast, at warmer temperatures, such as 104°F (40°C), viability decreases dramatically, often becoming non-infectious in hours. This stability at lower, above-freezing temperatures is why cold weather helps the virus persist on surfaces like plastic and stainless steel.
Understanding Freezing: Preservation Versus Destruction
A common misconception is that freezing, like temperatures found during deep winter or inside a freezer, will automatically kill a virus. In reality, freezing temperatures are used in laboratory settings to deliberately preserve viruses, including SARS-CoV-2, for future study. This process, known as cryopreservation, maintains the virus’s structure and infectivity indefinitely.
To render a virus non-infectious, scientists use inactivation, typically involving high heat or chemical treatment. For example, the virus can be fully inactivated by being held at 149°F (65°C) for 15 minutes. By contrast, samples stored at temperatures like -4°F (-20°C) or even ultra-low temperatures like -112°F (-80°C) maintain a stable, infectious titer for weeks or months. This demonstrates that freezing is a form of preservation, not destruction.
Cold Weather’s Impact on Transmission Rates
While cold helps the virus survive on surfaces, cold weather also dramatically influences person-to-person transmission rates through environmental and behavioral changes. A significant factor is the drop in humidity that accompanies colder air, especially indoors when heating systems are running. Lower relative humidity, often below the recommended 40% to 60% range, causes respiratory droplets to shrink rapidly.
These smaller, drier droplets remain suspended in the air longer, forming aerosols that travel further and penetrate deeper into the lungs. Dry winter air also impairs the respiratory system’s natural defenses, such as the mucous lining and cilia, making the host more susceptible to infection. The combination of increased viral persistence and weakened host defenses contributes to the seasonal spike in respiratory illnesses.
Behavioral changes also play a major part, as people spend more time indoors in poorly ventilated spaces during cold weather. Increased indoor congregation raises the density of infectious aerosols, leading to a higher exposure risk. Thus, cold weather drives up transmission rates by creating optimal conditions for viral survival and enhancing the probability of human exposure.