A common superstition, the five-second rule states that food dropped on the ground will not be contaminated with bacteria

Bacteria

Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

 if it is picked up within five seconds of being dropped. Some may earnestly believe this assertion, whereas other people employ the rule as a polite social fiction to prevent their having to forgo eating something that dropped.

There are many variations on the rule. Sometimes the time limit is modified. In some variations, the person picking up the food arbitrarily extends the time limit based on the actual amount of time required to retrieve the food. In Russia

Russia

Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...

 there exists a similar rule: "Promptly picked up is not considered fallen".

Research

The five-second rule has received some scholarly attention, and has been studied as both a public health recommendation and as a sociological effect.

In 2002, intern Jillian Clarke of the University of Illinois at Urbana–Champaign found in a survey that 56% of the men and 70% of the women surveyed were familiar with the five-second rule. She also determined that a variety of foods were significantly contaminated by even brief exposure to a tile inoculated with E. coli

Escherichia coli

Escherichia coli is a Gram-negative, rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms . Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in humans, and are occasionally responsible for product recalls...

. On the other hand, Clarke found no significant evidence of contamination on public flooring. Clarke received the 2004 Ig Nobel Prize

Ig Nobel Prize

The Ig Nobel Prizes are an American parody of the Nobel Prizes and are given each year in early October for ten unusual or trivial achievements in scientific research. The stated aim of the prizes is to "first make people laugh, and then make them think"...

 in public health for this work.

A more thorough study in 2006 using salmonella

Salmonella

Salmonella is a genus of rod-shaped, Gram-negative, non-spore-forming, predominantly motile enterobacteria with diameters around 0.7 to 1.5 µm, lengths from 2 to 5 µm, and flagella which grade in all directions . They are chemoorganotrophs, obtaining their energy from oxidation and reduction...

 on wood, tiles, and nylon carpet found that the bacteria were still thriving after twenty-eight days of exposure under dry conditions. Tested after eight hours' exposure, the bacteria could still contaminate bread and bologna in under five seconds, but a minute-long contact increased contamination about tenfold (with tile and carpet surfaces only).
The five-second rule was also featured in an episode of the Discovery Channel series MythBusters

MythBusters

MythBusters is a science entertainment TV program created and produced by Beyond Television Productions for the Discovery Channel. The series is screened by numerous international broadcasters, including Discovery Channel Australia, Discovery Channel Latin America, Discovery Channel Canada, Quest...

. There was no significant difference in the number of bacteria collected from 2 seconds exposure as there was from 6 seconds exposure. The moisture, surface geometry and the location the food item was dropped on did, however, affect the number of bacteria.

Ted Allen put the rule to the test in an episode of Food Detectives

Food Detectives

Food Detectives a food science show hosted by Ted Allen that airs in North America on Food Network. Ted Allen, backed by research conducted by Popular Science magazine, investigates various food-related beliefs, such as the validity of the five-second rule or the effectiveness of ginger as a means...

, and found that bacteria will cling to food immediately. High traffic areas will lead to even more bacteria on the food.

A team from Clemson University

Clemson University

Clemson University is an American public, coeducational, land-grant, sea-grant, research university located in Clemson, South Carolina, United States....

 conducted a study measuring the bacteria levels on classic 5 second rule locations such as outdoor soil, the sidewalk, kitchen counters and kitchen floors.

In popular culture

One of the main ideas of the live-action/animated film

Live-action/animated film

A live-action/animated film is a motion picture that features a combination of real actors or elements: live-action and animated elements, typically interacting.-History:...

 Osmosis Jones

Osmosis Jones

Osmosis Jones is a 2001 live-action/animated comedy film directed by Tom Sito and Piet Kroon for the animated segments and the Farrelly brothers for the live-action segments...

is the "ten-second rule", where "Frank Detorre", the character played by Bill Murray

Bill Murray

William James "Bill" Murray is an American actor and comedian. He first gained national exposure on Saturday Night Live in which he earned an Emmy Award and later went on to star in a number of critically and commercially successful comedic films, including Caddyshack , Ghostbusters , and...

, is infected by eating filthy food that has fallen to the floor of a chimp's cage at the zoo.

In Season 5 Episode 5 of Grey's Anatomy

Grey's Anatomy

Grey's Anatomy is an American medical drama television series created by Shonda Rhimes. The series premiered on March 27, 2005 on ABC; since then, seven seasons have aired. The series follows the lives of interns, residents and their mentors in the fictional Seattle Grace Mercy West Hospital in...

, Meredith drops a kidney on the floor during a transplant procedure. Chief Resident Dr. Bailey promptly shouts "Five second rule!", the kidney is safely donated afterward.

Craig Ferguson

Craig Ferguson

Craig Ferguson is a Scottish American television host, stand-up comedian, writer, actor, director, author, and producer. He is the host of The Late Late Show with Craig Ferguson, an Emmy Award-nominated, Peabody Award-winning late-night talk show that airs on CBS...

 used the "five second rule" on The Late Late Show with Craig Ferguson

The Late Late Show with Craig Ferguson

The Late Late Show with Craig Ferguson is a Peabody Award-winning American late-night talk show hosted by Scottish American comedian Craig Ferguson. Ferguson, the third regular host of the Late Late Show franchise, follows Late Show with David Letterman in the CBS late-night lineup...

during "Rather Late Night with Prince Charles" comedy sketch, when he accidentally dropped his teeth on the floor.