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Which Acne Medication Can Really Zap That Zit?

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Have you ever wondered where acne comes from and how you can treat it? One major cause of acne is the colonization and infection of clogged pores with bacteria. In this science project, you'll test different acne medications and treatments to determine their effectiveness at killing bacteria.


Areas of Science
Time Required
Average (6-10 days)
Material Availability
A kit for this project is available from our partner Home Science Tools. If possible, conduct this project in a laboratory with access to a bunsen burner and incubator.
Average ($50 - $100)
Follow the general safety precautions for handling microorganisms outlined at the end of the Procedure for this science project.

Sandra Slutz, PhD, Science Buddies

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In this science fair project you will determine which over-the-counter acne medications are the most effective at stopping the proliferation of E. coli.


Have you ever had acne? Almost everyone has! Clinicians estimate that nearly 100% of the population will have acne at some time during their lives, usually as adolescents. Acne forms in pilosebaceous units, which are compromised of a hair; a follicle, or shaft in the skin through which the hair grows; and a sebaceous gland. The sebaceous gland produces an oily substance, sebum, which protects the skin and hair, making them waterproof and preventing them from drying out. Dead keratinocytes, or skin cells, and excess sebum can clog the pilosebaceous unit. The clogged follicles are ideal environments for the bacteria that normally live benignly on the skin's surface, to proliferate. This proliferation causes local inflammation and the visual signs are referred to as acne.

Diagram of a hair follicle and sebaceous gland

Diagram showing glands under the skin near a hair follicle. Sebaceous glands are found on either side of a hair follicle and produce sebum which travels up the shaft of the hair towards the surface of the skin.

Figure 1. This diagram shows the components of a normal pilosebaceous unit, including the follicle and sebaceous gland. (NIAMS, 2006.)

One way to treat acne is to stop the proliferation of the bacteria. In this science fair project, you will test a variety of over-the-counter acne medications to determine which is the most effective at preventing bacterial proliferation. Although Propionibacterium acnes (P. acnes ) is the bacteria which most frequently contributes to acne, in this science fair project you'll be using the bacterium Escherichia coli (E. coli). E. coli is safer and easier to work with. You'll use the Kirby-Bauer disk-diffusion method to measure the effectiveness of each acne medication. With this technique, bacteria is uniformly spread across an agar plate, then sterile disks, each coated with a compound (in this case, medication) to be tested, are placed on the surface of the agar. The compounds diffuse out from the disk into the agar. The concentration of the compound is highest right next to the disk and gradually reduces as you move out in concentric circles from the disk. If a compound is effective against the bacteria at a certain concentration, no colonies will grow in the area of the plate where that compound is equal to or higher than the effective concentration. The areas without bacterial growth are called zones of inhibition and are characterized by a clear circle around the disk in an otherwise contiguous lawn of bacteria. The larger the zone of inhibition is, as measured by the diameter of the clear circle, the more effective the compound.

Bacteria in an agar plate avoids growing around circular inhibition zones created by small pieces of filter paper
Figure 2. The zones of inhibition are the clear circles surrounding the disks in the bacterial lawn. The size of each zone is measured with a ruler, and the data is recorded in a lab notebook. (D.M. Rollins and S.W. Joseph, 2000.)

Terms and Concepts



Here are some resources about acne to get your background research started.

  • American Academy of Dermatology. (n.d.). Acne. Retrieved April 20, 2018.
  • National Institute of Arthritis and Musculoskeletal and Skin Diseases. (2006, January). Questions and Answers About Acne. Retrieved April 9, 2008.

This animation from the CCBC Faculty Web shows the complete procedure and use of the Kirby-Bauer disk-diffusion method in a clinical setting. The bacterial growth conditions are different in this project, but the basic concept is the same. The last section covers how to interpret the results of the test, which will be particularly useful for your science fair project.

This website explains the Kirby-Bauer Disk-Diffusion method.

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Experimental Procedure

Working with Biological Agents

For health and safety reasons, science fairs regulate what kinds of biological materials can be used in science fair projects. You should check with your science fair's Scientific Review Committee before starting this experiment to make sure your science fair project complies with all local rules. Many science fairs follow Regeneron International Science and Engineering Fair (ISEF) regulations. For more information, visit these Science Buddies pages: Project Involving Potentially Hazardous Biological Agents and Scientific Review Committee. You can also visit the webpage ISEF Rules & Guidelines directly.

This science fair project involves the use of a classroom-safe strain of E. coli. While it is not considered a biohazardous or dangerous bacterial strain, it is important to always properly clean and dispose of bacteria and supplies that come in contact with it. See the Bacterial Safety Guidelines for more details on how to handle bacterial cleanup and waste.

Preparing Plates for Acne Medication Effectiveness Test

  1. Label your nutrient agar plates.
    1. Petri dishes should always be labeled in permanent marker and on the bottom of the plate. Labeling the lid is not sufficient as the lid is removable and might accidentally get swapped with another plate.
    2. Three of the plates are controls to make sure your bacterial lawns grow well and evenly. Label these plates: Control #1, Control #2, and Control #3.
    3. The other plates are your actual acne medication trial plates. Divide each plate into four equally sized quadrants with the permanent marker. See Figure 3 for an example.
      • Label one quadrant on each plate Water. This will be your negative control.
      • The other three quadrants should be labeled with the names of three different acne medications you are testing.
      • Each acne medication will be tested three times, but it should be tested on three different plates so that the maximum amount of experimental error is accounted for in your observations. Do not put all three replicates of an acne medication on the same plate.

      So, for every three acne medications you will label three plates where the quadrants read:

      1. Water, Acne medication 1A, Acne medication 2A, Acne medication 3A
      2. Water, Acne medication 1B, Acne medication 2B, Acne medication 3B
      3. Water, Acne medication 1C, Acne medication 2C, Acne medication 3C
An agar plate is labeled and divided into quadrants of water, medication, 2A and 3A
Figure 3. This photo shows how your agar plates should be divided into quadrants and labeled.
  1. Boil a small amount of water in a pot for 5 minutes. After boiling, put a lid on the pot and let it cool to room temperature. This is your sterile water.
  2. To make your bacterial lawns, you will need to work in a sterile environment. Work next to a lighted Bunsen burner, but be careful around the flame! If you have long hair, tie it back. Do not wear flowing sleeves, and avoid reaching across the flame. If a Bunsen burner is not available, work next to a lit candle.
    1. Take out your E. coli culture and follow the instructions in the kit to reconstitute the dried bacteria. Wait 5 minutes after reconstituting, then mix the gently shake to mix the bacterial suspension one more time.
    2. Put 2 drops E. coli culture on the surface of an agar plate. Try to put the culture in the center of the plate.
    3. Use a sterile cotton swab to spread the bacteria around the entire surface of the agar plate. Put the lid on the plate as soon as you are done.
    4. Repeat for the rest of the agar plates using a fresh cotton swab every two to three plates.
  3. After you have spread all your agar plates, wait 5 minutes for the surface of the plates to dry. Remember, keep those plates covered!
  4. Now you are ready to apply the negative control (sterile water) and medications to the agar plates.
    1. Do not add any substances to the three control plates.
    2. The remaining plates will each get a negative control—a disk dipped in sterile water—and up to three disks dipped in different acne medications.
      • Sterilize a pair of forceps or tweezers by dipping them in the isopropyl alcohol, then holding them in the Bunsen burner (or candle) flame for a few seconds. Let the metal cool for 1 minute before proceeding.
      • Using sterile forceps or tweezers, dip a sterile disk into the first acne medication you want to test. Gently remove shake or scrape off the extra medication without touching the disk.
      • Make sure that the label on the underside of the plate matches the medication you are testing. Place the disk in the middle of the appropriate quadrant on one of the agar plates. See Figure 4 for an example. Using the forceps, press down gently to ensure good contact between the agar plate and the disk.
      • Clean and re-sterilize the forceps between each use.
      • Repeat so that you have three plates for each acne medication.
      • Using the same technique, dip a disk in the sterile water. Apply one disk of sterile water to each agar plate. This will serve as a negative control. Sterile water should not create zones of inhibition; if zones do appear, you have a cross-contamination problem.
An agar plate is divided into quadrants with a small white disk at the center of each quadrant
Figure 4. The experimental plates should look similar to this once you have applied the medicated disks to the agar.

Measuring Zones of Inhibition

  1. After 48 hours of incubation (72-96 hours if you are not using a 37°C incubator), examine your plates (keep the lids on while you do this).
    1. Do you see a lawn of bacteria on the three control plates you made? If not, incubate the plates for an additional 24-48 hours until there is a decent bacterial lawn.
    2. The three control plates should show relatively uniform lawns. If you see dense bacterial growth in some areas and swatches of light or no bacterial growth in other areas, then your bacteria-spreading technique needs improvement. You will need to repeat the experiment again, paying special attention to spreading the E. coli culture across the plates to get reliable data.
    3. If the medications you chose are effective at preventing E. coli growth, you should see zones of inhibition around the medication disks. The clear zones around each disk should be circular with a relatively uniform diameter since diffusion of the substances through the agar is the same in every direction. If the zones of inhibition do not have uniform diameters, there are two possible problems:
      • The medication was not distributed evenly across the disk.
      • There was poor contact between the disk and the agar.
      • If the variability is particularly high, you might want to repeat the experiment, paying careful attention to how you apply the acne medications.
    4. There should be no zone of inhibition around your sterile water controls.
  2. Using a ruler, measure, in millimeters (mm), the diameter of the zone of inhibition around each medication disk. Do not take the lids off to do this. Instead, invert the plates and measure with the agar side closest to you. Record all your data in a data table in your lab notebook. You will have three measurements for each medication, each from a different plate.
  3. Analyze your data. Are the sizes of the zones of inhibition consistent across your replicates? Calculate the average and standard deviation for the medications you tested. Which acne medication was most effective; which was least effective?
  4. If you cross-compare the active ingredients in each medication with the results of your experiment, do you see any trends? Are there certain ingredients that seem to contribute significantly to preventing E. coli growth? If so, consider designing an additional experiment to test your new hypothesis.

Bacterial Safety

Bacteria are all around us in our daily lives and the vast majority of them are not harmful. However, for maximum safety, all bacterial cultures should always be treated as potential hazards. This means that proper handling, cleanup, and disposal are necessary. Below are a few important safety reminders.

  • Keep your nose and mouth away from tubes, pipettes, or other tools that come in contact with bacterial cultures, in order to avoid ingesting or inhaling any bacteria.
  • Make sure to wash your hands thoroughly after handling bacteria.
  • Proper Disposal of Bacterial Cultures
    • Bacterial cultures, plates, and disposables that are used to manipulate the bacteria should be soaked in a 10% bleach solution (1 part bleach to 9 parts water) for 1–2 hours.
    • Use caution when handling the bleach, as it can ruin your clothes if spilled, and any disinfectant can be harmful if splashed in your eyes.
    • After bleach treatment is completed, these items can be placed in your normal household garbage.
  • Cleaning Your Work Area
    • At the end of your experiment, use a disinfectant, such as 70% ethanol, a 10% bleach solution, or a commercial antibacterial kitchen/bath cleaning solution, to thoroughly clean any surfaces you have used.
    • Be aware of the possible hazards of disinfectants and use them carefully.
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Ask an Expert

Do you have specific questions about your science project? Our team of volunteer scientists can help. Our Experts won't do the work for you, but they will make suggestions, offer guidance, and help you troubleshoot.


  • The science fair project above does not distinguish between bacteriocidal and bacteriostatic compounds. Those that are bacteriocidal kill the bacteria, whereas those that are bacteriostatic temporarily inhibit bacterial growth. Devise an experiment to test whether the acne medications are bacteriocidal or bacteriostatic. You should only test the medications which proved effective against E. coli (i.e. those with the largest zones of inhibition).
  • Do any of the zones of inhibition have one or a few colonies within an otherwise bacterial-growth-free area? If so, think about what could be different about these colonies. Design an experiment to test your hypothesis.
  • Which antibiotics is E. coli susceptible to? Design an experiment to find out. Note: Antibiotic sensitivity disks are available from online suppliers such as Sargent-Welch and Carolina Biological.


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General citation information is provided here. Be sure to check the formatting, including capitalization, for the method you are using and update your citation, as needed.

MLA Style

Science Buddies Staff. "Which Acne Medication Can Really Zap That Zit?" Science Buddies, 17 Apr. 2023, https://www.sciencebuddies.org/science-fair-projects/project-ideas/MicroBio_p019/microbiology/acne-zits-medication. Accessed 30 Sep. 2023.

APA Style

Science Buddies Staff. (2023, April 17). Which Acne Medication Can Really Zap That Zit? Retrieved from https://www.sciencebuddies.org/science-fair-projects/project-ideas/MicroBio_p019/microbiology/acne-zits-medication

Last edit date: 2023-04-17
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