The popular five-second rule holds that food dropped on the floor may still be safe to eat if it is picked up within a few seconds. Research over the past two decades shows that time plays a role in how much bacteria transfers, but other factors such as moisture, surface type, and the level of contamination matter far more than the number of seconds on the floor.

Five Second Rule

Paul Dawson, a professor of food science at Clemson University, helped renew interest in the five-second rule by publishing a summary of research on the topic. His Clemson lab previously conducted a 2007 peer-reviewed study testing how bacteria transfer from different surfaces to food. Tile, carpet, and wood were inoculated with Salmonella, and bread and bologna were placed on the surfaces for 5, 30, and 60 seconds. Tests were also repeated after allowing bacteria to remain on the surfaces for up to 24 hours.

Those tests found that time was far less important than the amount of bacteria present. Carpet transferred only about 1 percent of bacteria, while tile and wood transferred as much as 70 percent. Dawson concluded that overall bacterial load mattered most, and that it generally decreased as surfaces dried out over time.

Other Early Tests

Dawson’s work was not the first attempt to investigate the five-second rule. In 2003, a high school student conducted tests by inoculating floor tiles and placing food on them for varying lengths of time. That study found that bacteria could transfer within five seconds, though the amount of bacteria transferred was not specified.

A 2014 study conducted in the UK also found that moist foods picked up more bacteria than dry foods. The study reported that carpet transferred the least bacteria and that the type of bacteria present on the floor was a major factor in determining risk.

The rule was also tested on the television series Mythbusters. Their test used moist pastrami and dry crackers for contact times of 2 and 6 seconds. All foods picked up bacteria regardless of time, with moist foods showing the greatest transfer. The show concluded that time alone was not a reliable measure of safety.

The 2016 Rutgers Study

In 2016, researchers at Rutgers University conducted one of the most detailed studies on the topic. They tested four types of food (watermelon, bread, bread with butter, and gummy candy) on stainless steel, tile, wood, and carpet at contact times ranging from less than one second to 300 seconds. The study found that bacteria could transfer almost instantly, even in under one second.

The researchers noted that time did affect bacterial transfer, but its impact was smaller than most people assume. Moist foods such as watermelon picked up the most bacteria, while foods with lower moisture content picked up less. Carpet again transferred the least, and tile and stainless steel transferred the most. Wood produced inconsistent results due to its porous nature.

Overall, the Rutgers team concluded that moisture level, surface type, and the level and type of bacteria present were far more important than the number of seconds food remained on the floor.

Bottom Line

Studies over the past twenty years show that bacteria can transfer to food the moment it touches the floor. Time does have some influence, but moisture, surface material, and the amount of bacteria present are the dominant factors. Clean, dry surfaces generally pose lower risk, while moist foods dropped on contaminated hard surfaces are most likely to pick up bacteria quickly. The five-second rule is not supported by scientific evidence, although real-world risk varies widely depending on conditions.

Revised and updated on November 24, 2025 from the original which appeared in 2015.