Whether double dipping is a disgusting habit, or a serious food safety and health threat, intrigued a team of researchers at Clemson University. A group of undergraduates decided to design a series of experiments to find out just what happens when someone double-dips.
Researchers set up experiments to see how much bacteria makes it from a person's mouth to a dip. The team started by comparing bitten crackers versus unbitten crackers. They measured how much bacteria could transfer from the cracker to a cup of water.
The results of the experiment showed close to 1,000 more bacteria per milliliter of water when crackers were bitten before dipping, when compared to water where unbitten crackers were dipped.
A second experiment involved researchers testing unbitten and bitten crackers in water solutions with pH levels typical of food dips. The pH levels consisted of 4, 5, and 6, which are all near the more acidic end of the pH scale.
Immediately after the bitten and unbitten crackers were dipped, the researchers tested for bacteria, and two hours later, they measured the solutions. Over time, bacterial numbers were lower in the more acidic solutions.
The next step was to test for bacteria in three kinds of dips, including cheese, chocolate, and salsa dips. Again, the team of researchers tested bacterial growth in the dips after already-bitten crackers were dipped, and after dipping with unbitten crackers.
They also tested the dips two hours after dipping to see how bacterial populations were growing. The results showed no evidence of bacteria in the absence of double dipping. However, after a dip was double-dipped, the salsa took on about five times more bacteria. These recent experiments are proof that double dipping can transfer bacteria from a person's mouth to a dip.
Hundreds to thousands of different types of viruses and bacteria live in a person's oral cavity – though most of them are harmless. On the other hand, some types of bacteria cause serious illness and can be deadly. Pneumonic plague, Legionnaires' disease, influenza virus, tuberculosis, and severe acute respiratory syndrome, or SARS, are known to spread through saliva -- with coughing and sneezing spraying close to 1,000 and 3,600 bacterial cells per minute.
These tiny germ-containing droplets from a cough or a sneeze can settle on surfaces, like desks, chairs, handrails, doorknobs, and especially shopping carts. Germs can be spread when a person touches a contaminated surface and then touches their nose, mouth, or eyes.
The Centers for Disease Control and Prevention strongly recommends people should cover their nose and mouth when sneezing and coughing to prevent spreading "serious respiratory illnesses like influenza, respiratory syncytial virus (RSV), whooping cough, and severe acute respiratory syndrome (SARS)."
Concern over spreading of bacteria from person to person, as a result of double dipping, is an important public health issue to consider. Additionally, germs can spread from person to person even though an invidicual is not ill.
According to Scientific American, a historical example of spreading diseases, while not showing any symptoms of an illness, is household cook Mary Mallon, or Typhoid Mary. Mary spread typhoid to a number of families in 19th-century New England while she was preparing food.
It's unclear whether Typhoid Mary tasted the food as she prepared it -- to all intents and purposes, double dipping. And Typhoid Mary may be considered an extreme example. Nevertheless, people who practice the habit of double dipping may be carrying flu or cold germs and passing them into a party dip.
If a double dipper is detected, it's best to stay away from their favored snack. In addition, everyone should take into consideration not double dipping when sick, or preferable avoid it all together.