Soap vs. Sanitizer- Teacher’s Notes 2010
Background:
According to the Center for Disease Control (CDC), the hands are one of the most
frequent transmission routes for many types of infections as they come into direct
contact with known portals of entry for pathogens (i.e. mouth, nose, conjunctiva of the
eyes). Therefore, practicing proper hand hygiene is the easiest way to help reduce
infections. Proper hand hygiene involves scrubbing your hands with soap and water for
at least 20 seconds. However, when water is not available, hand sanitizer can be an
effective alternative (but not a replacement) for cleansing your hands.
Hand sanitizer works because of the high concentration of alcohol (>60%).
Alcohol kills most bacteria and viruses by disrupting the cell or particle coating.
However, hand sanitizer does not work effectively if it is not applied properly- at least a
dime-sized amount rubbed all over your hands for no less than 30 seconds. A person
who uses hand sanitizer is likely to show slower redevelopment of bacteria. The use of
hand sanitizer in school is also relatable to a drop in illness rates and better records.
The manufacturers of the products test the products on inanimate surfaces hence
they are able to derive the claims of 99.9% of bacteria killed. If the products were fully
tested on hands, there would no doubt be different results. Since there is inherent
complexity in the human hand, testing hands would definitely be more difficult. Using
surfaces with controlled variables is an easier way to obtain some type of consistency in
the results. But as we are all aware, everyday life is not as consistent.
Unlike the active ingredients in some instant hand sanitizers and anti-bacterial
soaps, laboratory testing has never shown alcohol-based hand sanitizers to lead to
bacterial resistance. No mechanism for resistance to alcohol has been described in
bacteria. Many sources indicate that for organisms to become resistant, low levels of the
chemical must remain on the hands for the organisms to adapt. The alcohol in alcoholbased hand sanitizers does not remain on the hands for long. Once your hands are
rubbed dry after application, the alcohol has evaporated completely.
CA Science Standards Addressed:
7.1.a. Cell Biology: Students know cells function similarly in all living organisms.
7.2.a. Genetics: Students know the differences between the life cycles and reproduction
methods of sexual and asexual organisms.
7.7.a. Investigation and Experimentation: Select and use appropriate tools and
technology (including calculators, computers, balances, spring scales, microscopes,
and binoculars) to perform tests, collect data, and display data.
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Minority Science Programs – School of Biological Sciences – University of California, Irvine
Soap vs. Sanitizer- Teacher’s Notes 2010
7.7.c. Investigation and Experimentation: Communicate the logical connection
among hypotheses, science concepts, tests conducted, data collected, and
conclusions drawn from the scientific evidence.
Materials:
Per group of 6 students:
 6 Petri dishes (Fisher, 08-757-13), with Luria-Bertani agar (Fisher, DF0445-17-4)
o Pre-poured plates available from VWR (100216-614)
 12 sterile swabs (Fisher, 14-959-91)
 12 vials of sterile water (Fisher, BP24701)
 Soap (Softsoap liquid)
 Antibacterial hand sanitizer (Purell)
 Gloves
 Tape, marker pen
 Plate grid
Preparation Notes:
Petri dishes with growth media should be prepared by the manufacturer’s
instructions (this requires an autoclave unless using pre-poured dishes). Use a
permanent marker to divide the bottom of each dish in half. Prepared plates may be
kept in the refrigerator for a few weeks before use. Always store Petri dishes upsidedown to reduce condensation. Aliquot the sterile water into sterile microcentrifuge
tubes. Test for bacterial contamination by plating a sample of water on a Petri dish.
The sampled Petri dishes may be incubated from 24-72 hours to achieve
appropriate growth for analysis. If the plates cannot be immediately analyzed, they can
be stored sealed in the refrigerator for a few days. All waste (used plates, gloves, swabs)
should be disposed of in biohazardous waste bags and autoclaved. Work surfaces should
be cleaned with 10% bleach and 70% alcohol after completion of the activity.
References:
Dix, K. (2002). “CDC’s endorsement of alcohol hand rubs launches new era in hand
hygiene.” Infection Control Today.
http://www.infectioncontroltoday.com/articles/400/400_2c1feat6.html
Accessed 2010/02/02.
Landau, E. (2009). “Hand sanitizer: How it protects you.” CNN Health.
http://www.cnn.com/2009/HEALTH/11/27/hand.sanitizer.basics/index.html
Accessed 2010/01/24.
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Minority Science Programs – School of Biological Sciences – University of California, Irvine
Soap vs. Sanitizer- Teacher’s Notes 2010
Reynolds, S.A., F. Levy, E.S. Walker (2006). “Hand Sanitizer Alert.” Emerging
Infectious Diseases 12(3): 527-529.
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Minority Science Programs – School of Biological Sciences – University of California, Irvine