Does storage temperature affect hand sanitizer’s effectiveness?

Our hypothesis is that hand sanitizer becomes less effective when it is stored at cold temperatures, used in small volumes, or contaminated.​ We will test by rubbing our dirty hands on Petri dishes and left it for two weeks. Then we will count the colonies of bacteria.

• Purell instant hand-sanitizer was developed in 1988.​

• Statistics Canada reported a 792% increase in the sales of hand sanitizer during the COVID-19 pandemic.​

• Nearly half of adults had not used hand sanitizer before pandemic, but used it multiple times (8+) per day by 2020.​

• Since then, 55 % of Canadian maintains the same sanitization frequency.​

• It kills 99.99 % of bacteria include several multidrug-resistant pathogens and coronaviruses.​

• It reduces spread of diarrhea and respiratory illness.

• ​There are reports on lack of knowledge and misuse of hand sanitizers.​

• Many kept hand sanitizer handy in cars, but few studies examined the storage temperature effects. ​

• Several studies recommended a single application of hand sanitizer of volumes ranging from 1.1 to 3 mL, whereas the FDA recommends 2.4 mL. ​

• Purell bottle pumps dispense 2.5mL, but other bottles pumps 0.75 to 1.5mL. ​

Manipulated variables: temperature, volume, contaminants

Responding variables: number of bacterial colonies on petri dish

​Controlled Variables​: Brand and alcohol % of sanitizer​, contact time (20 seconds rubbing)​, agar type​, incubation time and temperature​, same person’s hand​

Control: Hands with NO hand sanitizer applied​ ​ ​

step one, get agar and petri dish. then pour the agar on the petri dish. then put hand sandizer in different tempature. then we lable the petri dish the made our hands dirty.hf

• When analyzed using median colony counts, hand sanitizer had 91% reduction rate when in room temperature. (Graph 1). ​

• Increasing hand sanitizer volume significantly improved bacterial reduction, with 100% reduction rate observed at 2 mL application (Graph 2).​

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• Organic contamination with dirt significantly lowered its effectiveness with 0% reduction while lotion on hands only slightly affected with 95% reduction (Graph 3). ​

• The back of a Purell hand sanitizer​ has vague directions stating:

• Apply enough product to the palm of one hand to thoroughly cover all surfaces, then briskly rub hands together for roughly 20 seconds until completely dry.

• Store below 43°C

• A survey showed 67% of Canadians leave hand sanitizer in the car, exposing the hand sanitizer in extreme temperatures. ​ ​

• Research showed that consumers may associate small packaging with limited supply, which could subconsciously encourage them to use smaller dabs.​ ​

• Proper storage, usage and handling is needed for maximize antimicrobial effect. ​

• Specific directions on labels will be useful for consumers and manufacturers. ​

• Hand sanitizer reached maximum effectiveness at room temperature.​

• From 0.5 mL to 2 mL of hand sanitizer demonstrated anti-microbial activity, with 2 mL the most effective. ​

• Dirt visible on-hands altered hand sanitizer effectiveness more than lotion.

• Don't store hand sanitizer long-term in a car​

• A small dab (0.5 mL) has some antimicrobial effect​

• For maximum effectiveness, use one full pump (\~2.5 mL)​

• If hands are dirty or have lotion on them, rinse with water before using sanitizer​

• After recess, children should wash hands before eating rather than rely only on sanitizer​

Sources of errors

• Small sample sizes​

• Uneven bacteria distribution ​

• Cross contamination​

• Counting Errors (merging of colonies)​

• Cracked Agar​

• Frierson A, Hurley RA, Kimmel RM, et al. The role of package design typicality on a hand sanitizer purchase. Packag Technol Sci. 2022; 35(10): 737-751. doi:10.1002/pts.2676​

• GOJO Industries. (2022). The PURELL story: Our 10‑year overnight success. https://www.gojo.com/en-CA/INT-Newsroom/Media-News/2022/The-PURELL-Story-Our-10-Year-Overnight-Success​

• LinkedIn. (n.d.). The evolution of the hand sanitizer market: From niche necessity to mass adoption [Graph]. https://www.linkedin.com/pulse/evolution-hand-sanitizer-market-from-niche-necessity-gvr-fmcg-aayvf#:~:text=The%20Future%20of%20the%20Hand,products%20that%20once%20seemed%20optional.​

• Lopez, T.K., Jones, K., Roseberry-Lincoln, A. et al. Adult and children’s use of hand sanitizer during a pandemic – an observational study. J Expo Sci Environ Epidemiol 33, 1004–1012 (2023). https://doi.org/10.1038/s41370-022-00479-Molom-Ochir, Sanchir & Davis, Kimberly. (2022). Effects of Temperature on Hand Sanitizer Efficiency. Journal of Emerging Investigators. 10.59720/21-120.​

• Pickering, A. J., Davis, J., & Boehm, A. B. (2011). Efficacy of alcohol‑based hand sanitizer on hands soiled with dirt and cooking oil. Journal of Water and Health, 9(3), 429–433.​

• Saha, T., Khadka, P., & Das, S. C. (2021). Alcohol‑based hand sanitizer—composition, proper use and precautions. Germs, 11(3), 408–417. https://doi.org/10.18683/germs.2021.1278​

Acknowledgement

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We would like to thank Ms. Caitlin Beams for her guidance. We would also like to thank our parents for their support.​

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River Valley School​

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Conversations with Pariya Edalet, Anita Kwong, Susan Sidorsky and Meredith Salisbury. ​

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