Perishable food, including pizza, should not be left out at room temperature for more than two hours. This time limit is based on food safety guidelines designed to prevent the rapid growth of bacteria that cause foodborne illness. The combination of cheese, meat, and sauce in a typical pizza creates an environment where microorganisms thrive quickly once the temperature drops below serving heat.
The Food Safety “Danger Zone”
The scientific principle behind the time limit is the “Danger Zone,” the temperature range where bacteria multiply most rapidly. Food safety agencies define this zone as temperatures between 40°F and 140°F (4°C and 60°C). Within this range, bacteria can double their population in as little as 20 minutes.
Pizza is considered a time and temperature control for safety (TCS) food because it contains dairy and often meat, which support bacterial growth. Once a hot pizza cools, it quickly enters the Danger Zone, becoming an ideal breeding ground for pathogens. The longer the pizza remains in this range, the higher the concentration of harmful bacteria becomes, increasing the risk of sickness.
The Critical Two-Hour Rule
The two-hour rule is the maximum safe time for any perishable food to be exposed to the Danger Zone before it must be refrigerated or discarded. This guideline minimizes the risk of foodborne illness for consumers. After two hours, the bacterial count is high enough to pose a significant health risk, even if the pizza is subsequently reheated.
An exception applies when the ambient temperature is particularly high. If the temperature is 90°F (32°C) or warmer, the safe time drops to just one hour. This reduction is necessary because the warmer environment accelerates bacterial growth, reaching unsafe levels faster. The danger is often invisible, as food can look and smell fine while containing high levels of harmful bacteria or their toxins.
How to Safely Store Leftover Pizza
To safely preserve leftover pizza, move it into cold storage promptly, ideally within the two-hour window. Transfer the slices from the cardboard box, which offers no insulation, into an airtight container or wrap them tightly. This helps prevent the pizza from drying out and protects it from absorbing odors or cross-contamination in the refrigerator.
Properly stored pizza remains safe to eat in the refrigerator for about three to four days, provided the temperature is maintained at or below 40°F (4°C). For longer storage, freezing is an option, maintaining quality for one to two months. To freeze slices, separate them with parchment paper and wrap the stack securely to prevent freezer burn.
When reheating safely stored pizza, ensure it reaches an internal temperature of 165°F (74°C) to eliminate any bacteria that may have grown during refrigeration. This temperature requirement is the safety standard. Reheating does not make pizza safe if it was left out past the two-hour limit, as some bacterial toxins are heat-resistant.