Efficiency of Hand Washing in Hot and Cold Water

Abstract

The purpose of this experiment was to determine which water temperature was most successful in the removal of pathogenic growth from handwashing. The experiment consisted of three participants which include: Taylor Pumo, Rebekah George, and Lexi Vendl. There were two procedures involved in this experiment. The first procedure was washing the left hand with bar soap in warm water. The second procedure was washing the right hand, with the same bar of soap, but with cold water instead. The hands were both washed for a duration of twenty seconds each. Every person has a preferred temperature they like to wash their hands in. However, this experiment showed which temperature was most effective in inhibiting bacterial growth. The results showed that washing hands in warm water vs cold water were very similar. The Petri plates for both hands were very close in the number of bacteria that had grown. The main reason for these results is due to rigorous handwashing. Intense scrubbing while washing hands can actually remove the body's natural flora. However, the results concluded that the most effective hand washing temperature was when the hands were washed in warm water.

Introduction

The significance of handwashing is constantly being drilled into a child’s head throughout their whole childhood. However, most people don’t truly realize its importance of it. Handwashing plays an essential role in decreasing the transmission of microorganisms, including pathogenic microorganisms, which result from contact, like handshaking. One of the first people to truly realize the importance of handwashing was, Ignaz Semmelweis. Ignaz discovered that puerperal fever resulted from the lack of handwashing. He realized that the medical students would come from performing autopsies and then straight to help deliver a newborn child. After realizing this, he made it mandatory for staff to wash their hands with a substance called chlorine. This resulted in a decreased spread of bacteria and a drop in the mortality rate. Furthermore, a few years after Semmelweis tried advocating the importance of hand washing, a nurse in Italy named, Florence Nightingale, tried to do the same thing. During this time, most people believed that infections were transmitted by odors in the air called miasmas (GHP). Nightingale introduced the technique of handwashing into the war hospitals she worked in. The results ended up showing a decline in the spread of infections. Although handwashing was still being used, it took over a century for people to truly realize its importance of it. People started to realize this when a foodborne outbreak started to become abundant. These food outbreaks started to occur during the 1980s. The public started to spark fear from these outbreaks that were happening. The United States Centers for Disease Control and Prevention realized that proper handwashing would be the only way to stop these pathogenic microorganisms. Since the public was so concerned about these outbreaks, The United States Centers for Disease Control and Prevention released the first national guideline for hand hygiene (GHP).

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The purpose of this experiment was to figure out the optimal hand washing temperature that would inhibit the most growth of pathogenic microorganisms. Most people were raised to believe that washing your hands with hot water would be the most effective. However, there has been a lot of controversies on which temperature works the best. The main purpose of hand washing is to get rid of transient microorganisms and to inhibit bacterial growth from growing on the skin (Gardner, 2019)​.​An article called “Impact of hand hygiene knowledge on hand hygiene compliance”, states that, “ 32.9% of the students did not perform hygienic hand washing properly”(Novak, 2019). These results showed that almost have of the experiment's population admitted to not having proper hand washing skills. Hand washing with hot water is believed to kill more bacteria rather than if you had washed your hands with cold water. The Food and Drug Administration (FDA) believes that washing hands in hot water and soap is the most effective way of removing pathogens. The FDA conducted a study to see which temperature was most optimal. Their results showed that temperature had no effect on the removal of bacteria (Sandoiu, 2017). On the contrary, a study published by the​Journal of Food Protection​had a different opinion. The data concluded from their experiment showed that washing hands in cold water worked at inhibiting the growth of bacteria just as well as hot water did (MacMillan).

The initial hypothesis before completing the experiment was that the warm water would inhibit the most growth of pathogenic bacteria. However, many experiments and analyses over the years have shown that all the optimal temperature for inhibiting the most growth was when hands were washed in warm water. The experiment conducted will visually show which temperature inhibited the most growth due to how much growth is on each individual petri dish. The hands were washed with Irish Spring bar soap for twenty seconds each to insure that the results would be more accurate. According to the Centers for Disease Control and Prevention, the optimal way for a person to wash their hands is to apply soap and lather all parts of the hands. The correct amount of time a person should lather for is around twenty seconds. This specific amount of time insures to get rid of most of the bacteria residing on the hands. A potential setback for this experiment that could potentially affect the data would be to much removal of the body’s resident flora. Resident flora is the body's natural microorganisms that reside on the skin and are not harmful. If the scrubbing is to harsh and removes a lot of the resident flora, it could result in more bacterial growth rather than less. This experiment is definitely a reminder on the importance of great hand hygiene.

Materials and Methods

Figure 1​: Irish Springs Original deodorant bar soap

The Imperative materials for this assignment included the lab manual, six blood agar Petri plates, a sharpie marker, Irish spring original deodorant bar soap (Figures 1), three participants, three pairs of latex gloves, a sink that has warm and cold water, paper towels, a timer, and an incubator set at 37 degrees Celsius. The experiment took place at Florida Gulf Coast University in Whitaker Hall, room 268, on Wednesday, September 18th, 2019, and the results were collected on Monday, September 23rd, 2019, in the same location. Before starting the experiment, make sure to check that the incubator is set to 37 degrees celsius for accurate results. The first major step in starting this experiment is to discuss and develop a research plan to find out which specific method is going to be used. There should only be one variable changed in this experiment to get accurate results. The participants had to decide which variables they were gonna use to find their results. The experimenters decided on using the Irish Springs bar soap has the handwashing material. Furthermore, the group decided that the left hand would be washed in warm water and the right hand would be washed in cold water. The participants then took about paper and pencil and recorded what was discussed and everything else that had taken place in the experiment. Each member was assigned two blood-infused agar Petri plates. The participants were in charge of labeling their own petri dish. The first petri dish was for the left hand. A line was drawn down the middle to separate both sides. The left side was indicated before treatment and the right side was indicated after treatment. This petri dish symbolized that the member's left hand was washed with warm water. The second Petris dish was labeled the same way. However, this petri dish symbolized the right hand. The right hand was to be washed in cold water. After differentiating which plate was which, each member put their initials and row numbers to ensure they knew which plates were theirs. The next step was to figure out the placement of the hands on the blood-infused petri dish. The members decided on using three fingers to collect data. The three fingers included the index phalange, middle phalange, and ring phalange. The members picked these specific fingers because it would be the easiest to place on the petri dish without touching the opposing side. The experiments then took the lid off the Petri dishes and pressed down the three fingers on the before-treatment side. The fingers were pressed onto the petri dish for 5 seconds. This was timed with a timer. This ensured that the before-treatment side of the right and left hand would have similar results.

Finally, after all the setup steps are done and recorded it was time for the next part of the experiment. This part of the experiment was the handwashing section. The participants discussed what techniques were going to be used to actually wash their hands. After discussing, the members agreed on washing each hand for twenty seconds each. The seconds would be timed with a timer to insure accuracy. The group also decided on doing the left hand first. A latex glove was placed over the right hand to ensure that it wouldn't get splashed with soap and water and inhibit the chance of any bacteria from leaving the hand. The members walked over to the sink, turned on the water, and let it run for a minute to ensure that the water would get warm. After the water was at optimal temperature, each experimenter wet the ungloved hand with the running water and started lathering the hand with the Irish Spring bar soap. This was trimmed for twenty seconds each. After the twenty seconds were up, each experimenter grabbed two paper towels to dry their hands. Next, they went back to their left-handed Petri dishes, opened them with the covered hand, and placed their three fingers on the after side. Finally, they closed the lid of the petri dish and disposed of the right-handed glove.

Similarly, the experimenters put a glove on the left hand and began the steps for the right hand. The right hand represented cold water. The members turned off the hot water using their gloved hands and changed the temperature to cold. They waited approximately one minute to ensure that the temperature was cold enough and began the same procedures as the left hand. After each member washed their hand for twenty seconds they dried their hand with two paper towels and pressed their fingers into the after side of the petri dish labeled right hand. After placing the fingers for three seconds, they closed the lid and recorded the steps they took.

When the experimenters finally completed all the steps, they carried their Petri dishes to the front of the classroom. They placed the dishes onto racks which would be sent to be incubated at 37 degrees Celsius. The Petri dishes will be incubated for five days to ensure accurate results. After the five days had passed, the members collected the dishes corresponding to them and inspected their results. As they observed their results, they counted and recorded the amount of bacterial growth on each plate. They then discussed all the possible factors that could have affected their results and wrote them down. The members then took pictures of their results on each petri dish for their lab report. Lastly, the Petri dishes were safely discarded into the hazardous bin in the back of the classroom.

Results

Figure 1​: Experimenter one’s left hand before ​Figure 2​: results from experimenter & after washing. one’s right hand before and after.

The plates above show the before and after growth of bacteria from experimenter one.

The left-handed petri dish shows that there was a slight increase in bacterial growth on the after side compared to before treatment. Figure one had 10 colonies before treatment and only around 27 colonies after bacteria. Most of these colonies probably represent resident flora. However, Figure 2 shows a considerably larger increase in bacterial growth compared to before treatment. As depicted in figure 2, their were approximately 31 colonies before treatment. After washing the hand, there were around 70 colonies of growth that were produced.

Figure 3: ​Illustrates Experimenter two’s Figure 4: Illustrates Experimenter two’s left-handed results. right-handed results.

The figures above both illustrate the before and after treatment in the result of hand washing. Figure 3 had only 11 colonies grow from the before-treatment side of the petri dish. In addition, the after-treatment side definitely had a greater increase in bacterial growth than the experimenter one. The left-handed side ended up with around 80 colonies after treatment. However, the right-handed petri dish, which was washed with cold water, initially had 20 colonies of growth before treatment and ended up with around 120 after treatment.

Figure 5​: Represents Experimenter three’s Figure 6​: Represents Experimenter three’s results of the left hand washed with warm water. results of the right hand were washed with cold water. As you can see, Figure 6 had significantly more growth in after treatment rather than figure five, which was washed in warm water. Figure five had approximately 22 colonies before treatment and only a slight increase of 40 after treatment. In comparison to Figure six which resulted in 24 colonies of growth before treatment and ended up with around 50 colonies of growth after treatment.

Graph 1: The amount of bacterial colony growth from each hand before and after treatment.

The bar graph depicted above represents the results from each participant. Each participant is labeled with a specific color. The results are categorized by a specific hand and if it was before treatment or after. The bar graph shows that the right hand after had the highest overall number in bacterial growth. The right had was washed with cold water. The left hand had the lowest average number in both bacterial growths before treatment and after treatment. These numbers help support that washing hands in warm water inhibited the most amount of growth.

Discussion

Once the experiment was fully conducted and the results were analyzed and recorded, it was clear to see which temperature inhibited the most bacterial growth. After carefully analyzing all of the results, it is believed that the optimal temperature of inhibiting the growth of bacteria would be when hands are washed with warm water. The hypothesis that was articulated during the start of the experiment was that washing hands in warmer water will have a greater impact in the inhibition of bacterial growth. The participants carefully reviewed the results and came to a conclusive decision that there were significantly lower colony numbers from the hand that was washed in warm water compared to the hand that was washed with cold water ( Graph 1). Although the numbers for the before treatment were higher than expected, our hypothesis is still supported by the data collected.

The members discussed possible factors that could have potentially affected the results of the experiment. For example, like mentioned earlier, the human body houses natural bacteria all over the skin. This bacteria is called resident flora. This resident flora can potentially help protect us from harmful pathogenic bacteria. The group concluded that harshly scrubbing the hands while washing them could potentially remove resident flora from the skin, leaving the hands vulnerable to harmful bacteria. This could have been a factor in having a higher amount of bacterial growth in our results. Furthermore, bacteria is lying on everyday objects that people use. Another factor that could have affected the accuracy of the results is if there was any bacteria on the paper towels used to dry the hands after being washed. The paper towels were placed in a rack, which makes them susceptible to any microorganisms floating around. To conclude, the members of the group used their best effort in order to minimize the factors that would affect the accuracy of the results.

Overall, the experiment was very eye-opening to how much bacteria we have on our skin before washing our hands and even after. Many people don’t realize the importance of good hand hygiene. The practice of healthy hand hygiene is crucial in the process of inhibiting and decreasing the spread of pathogenic bacteria. If the topic of proper hand hygiene was talked about more, people realized how much bacteria lives on the human body, and how it can grow even if someone washed their hands, then more people would start developing better hand washing skills.

References

1. Cdc.gov. (2019). When​ and How to Wash Your Hands | Handwashing | CDC​.[online] Available at: https://www.cdc.gov/handwashing/when-how-handwashing.html [Accessed 12 Oct. 2019].
2. Gardner, D. (2019). How​ To Perform Surgical Hand Scrubs​.[online] Infection Control Today. Available at: https://www.infectioncontroltoday.com/hand-hygiene/how-perform-surgical-hand-scrubs [Accessed 13 Oct. 2019].
3. MacMillan, A. (n.d.). Why You Should Wash Your Hands in Cold Water. Retrieved from https://time.com/4800412/wash-hands-cold-water/.
4. Novak, M. (2019). [online] Ljkzedo.ba. Available at: http://ljkzedo.ba/mgpdf/mg32/11_Novak_1051_A.pdf [Accessed 12 Oct. 2019].
5. Sandoiu, A. (2017, May 31). Handwashing with cold water just as good as hot water for killing bacteria. Retrieved from https://www​.medicalnewstoday.com/articles/317712.php.​