Many people wonder whether cold temperatures effectively eliminate germs or simply render them inactive. The general understanding is that cold primarily inhibits microbial growth rather than outright killing most germs. This distinction is important for understanding food safety, illness transmission, and effective sanitation practices.
How Cold Affects Germs
Cold temperatures slow the metabolic processes of microorganisms like bacteria, viruses, and fungi. Each microbe has an optimal temperature range for growth, and activity decreases below this range. Refrigeration, around 4°C (40°F), slows the growth and reproduction of most bacteria, putting them into a dormant state. Freezing, at -18°C (0°F) or lower, halts microbial growth by forming ice crystals. While some microbes are damaged or killed by ice crystals, many survive freezing and reactivate upon thawing.
Cold Storage and Food Safety
Cold’s effect on germs is applied in food preservation. Refrigeration and freezing are important for preventing food spoilage and inhibiting pathogenic bacteria that cause foodborne illnesses. Refrigerators should be kept at 4°C (40°F) or below, and freezers at -18°C (0°F) or lower, to keep food out of the “danger zone” where bacteria multiply rapidly.
Cold storage does not sterilize food or kill all existing bacteria. Some bacteria, like Listeria monocytogenes, can even grow at refrigerator temperatures, emphasizing the need for proper cooking and hygiene. Thawing frozen foods safely—in the refrigerator, under cold running water, or in the microwave—is also necessary to prevent bacterial growth before cooking.
Cold Weather and Illness
A common misconception is that cold weather directly causes illnesses like the common cold or flu. Viruses cause these illnesses, not cold exposure itself. However, cold weather can indirectly influence the transmission and severity of viral infections.
People spend more time indoors in close proximity during colder months, increasing virus spread. Dry air associated with cold weather can dehydrate respiratory mucous membranes, making them more susceptible to viral infection. Cooler temperatures can also weaken the immune response in the nasal cavity, making it harder to fight off viruses.
Methods for Killing Germs
Since cold primarily inhibits rather than kills germs, other methods are necessary for effective sanitation and disinfection. Heat is an effective germ killer, as it denatures proteins and destroys the cellular structures of microorganisms. Cooking foods to specific internal temperatures, above 60-75°C (140-165°F) depending on the food type, is important for killing harmful bacteria and viruses. Boiling water at 100°C (212°F) for at least one minute also effectively eliminates most harmful bacteria, viruses, and parasites.
Chemical disinfectants, such as bleach, alcohol-based sanitizers (at least 70% alcohol), and hydrogen peroxide, work by damaging microbial cell walls or interfering with their metabolism. Regular cleaning with soap and water mechanically removes germs and dirt from surfaces, reducing their numbers and preventing infection spread.