The Skinny on Moisturizers: Which Works Best to Keep Skin Moist?

Preparing the Skin Models

In this part of the science project, you will prepare your petri dishes with the skin models (JELL-O gelatin dessert). As a control, you will prepare three dishes with the gelatin dessert only (you will not add any skin moisturizers to them).

1. Assign a number to each skin moisturizer you want to test.
   1. Use the permanent marker to label the containers, as shown in Figure 3, or you can write these numbers down in your lab notebook along with the moisturizer's name.
   2. This will make it easier for you to keep track of your results.

Figure 3. Number the skin moisturizers, either by using a permanent marker to label the containers, as shown here, or by writing numbers for the names of each moisturizer in your lab notebook.

2. In your lab notebook, also assign a number to the control samples that contain only the gelatin dessert.
3. Label three petri dishes for each skin moisturizer you want to test, plus three dishes for the gelatin dessert-only controls.
   1. You will be testing each sample in triplicate because repeating your results like this helps show that they are accurate and reproducible.
   2. Use a permanent marker to label the edge of the petri dishes with the skin moisturizer and control numbers (do not label the lids). For each dish with the same number, also write a letter on that dish, such as "5a," "5b," and "5c," so that each dish is uniquely labeled. Figure 4 shows an example.

Figure 4. Use a permanent marker to label the edge of each petri dish with the skin moisturizer number and a letter so the dish is uniquely labeled. (The label "5a" is used as an example.)

4. Follow the instructions on the gelatin dessert packaging to prepare at least 50 milliliters (mL) of gelatin dessert for each petri dish. You should prepare a little extra gelatin dessert in case some is lost while transferring it to the dishes.
   1. If you want to fill 18 petri dishes with gelatin dessert, you need to prepare at least 900 mL of it (18 x 50 mL = 900 mL).
   2. A 3 ounce (oz.) package of gelatin dessert can be used to prepare 473 mL (2 cups) of gelatin dessert. So if you want 900 mL of it, you need to prepare at least two 3-oz. gelatin dessert packages (because one package will give you 473 mL, and two packages will give you 946 mL).
   3. Prepare the gelatin dessert packages together, following their instructions. You may want to ask an adult to help you use the stove.
      1. On the stove, boil 1 cup of water per package, add the gelatin dessert mixes to the boiling water, then stir continually for two minutes (while keeping the pot on the hot burner). The mixture should look clear (but probably colored) and it should barely start boiling again after the two minutes are up.
      2. Take the gelatin dessert mixture off of the hot burner and add 1 cup of cold water per package, stirring it in as it is added. Immediately go on to step 5.
5. Pour 50 mL into each petri dish.
   1. Use a cup with a pouring spout to ladle the gelatin dessert mixture out of the pot and pour it into the 50 mL graduated cylinder.
   2. Slowly pour the 50 mL of gelatin dessert into each petri dish (one at a time) to avoid splashing any gelatin dessert out of the dish.
   3. Work as quickly as you can without spilling too much gelatin dessert. This step can easily become messy, so try to work only over surfaces that are easy to clean.
   4. The 50 mL of gelatin dessert should fill each petri dish a little more than halfway, as shown in Figure 5.

Figure 5. Pouring 50 mL of gelatin dessert into a petri dish should fill it a little more than halfway.

6. When you have poured 50 mL of gelatin dessert into all the dishes, put their lids back on and carefully move them to a shelf in the refrigerator where they will not be disturbed for four hours.
   1. Move slowly and carefully to avoid spilling any gelatin dessert while you move the dishes.
   2. You can stack the dishes carefully to save space in the refrigerator.
7. After refrigerating the dishes for four hours, the gelatin dessert should be firm. Take the petri dishes out of the refrigerator and immediately go on to the next section in the Procedure, "Testing the Skin Moisturizers." You can keep the petri dishes at room temperature for the rest of the experiment.

Testing the Skin Moisturizers

In this part of the science project, you will add the skin moisturizers you want to test to the petri dishes you prepared and then investigate how the JELL-O gelatin dessert and skin moisturizers change over the next two weeks. You will investigate this by weighing all the petri dishes over time (including the controls, which will have no moisturizers added) and by measuring the change in height of the gelatin dessert in the dish. You will assume that weight and height loss is mostly due to water that has been lost (i.e., evaporated).

1. In your lab notebook, create two data tables: one like Table 1 and a second like Table 2. You will be recording your results in these data tables.

2. Remove the lid from each petri dish and set the lids aside (they are no longer needed for this project).
3. Use paper towels or rags to wipe away any gelatin dessert on the outside (such as the sides or bottom) of the dishes.
4. Weigh each petri dish and record its weight (as "JELL-O Alone Before Adding Moisturizer") in Table 1 in your lab notebook.
5. Using a ruler, measure the height (in centimeters [cm]) of the JELL-O in each dish, including the controls, as shown in Figure 6. Record this data (as "JELL-O Alone Before Adding Moisturizer") in Table 2 in your lab notebook.

Figure 6. Measure the height of the gelatin dessert in each dish.

6. Add 2 tablespoons (tbsp.) (30 mL) of the correct skin moisturizer to each petri dish.
   1. This may be easiest to do using a measuring tablespoon and pieces of plastic wrap to scoop the moisturizer out of the measuring tablespoon. (Either put the plastic wrap around your fingers to scoop out the moisturizer or you could try lining the measuring tablespoon with plastic wrap.) Use a fresh piece of plastic wrap for each moisturizer, and clean the tablespoon between moisturizers, so you do not contaminate your samples.
   2. Make sure the moisturizer covers the entire surface of the gelatin dessert in a thick layer. The layer will probably go up to around the rim of the dish, as shown in Figure 7.
   3. Smooth out the surface of the moisturizer using a plastic or butter knife. Use a new knife (or clean the one you re-use) for each dish.
   4. Do not forget to leave three petri dishes with gelatin dessert only and no moisturizer as controls.
   5. In your lab notebook, record any observations about how each moisturizer looks and feels. Are you surprised by the appearance and feel of any of them, based on what you know of their ingredients?
   6. When you have finished, record what time it is so that you will know the elapsed time since you added the moisturizers to the dishes.

Figure 7. When you add 2 tbsp. of a skin moisturizer to a petri dish, it should fill up the dish to around the rim, as shown here.

7. As soon as you have finished with step 6, weigh each petri dish again and record its weight as "0 hours" in the Table 1 in your lab notebook. Also measure the height of the gelatin dessert (not including the moisturizer) in each petri dish again and record the height as "0 hours" in Table 2. Keep the dishes on a flat surface while measuring their height so that moisturizer does not spill out.
8. If you have a camera, take a picture of each petri dish at this time.
9. Again weigh, and measure the height of the gelatin dessert in, the dishes at one, two, three, four, eight, and 16 hours after you added the skin moisturizer. Write their weights and gelatin dessert heights in the corresponding data tables in your lab notebook.
   1. If you cannot do these exact time points, write the actual time points you use (in hours) in your data tables.
10. Then continue to weigh, and measure the gelatin dessert heights of, the dishes every 24 hours (after adding the skin moisturizer) and write the dishes' weights and gelatin dessert heights in the corresponding data tables. Do this for a total of two weeks.
    1. When you check the dishes each day, also record in your lab notebook any other observations you make over time, such as if and when the moisturizer on any of the dishes starts to develop cracks.
11. After two weeks, make more detailed observations on how the skin moisturizer in each dish looks. Record your observations in your lab notebook.
    1. If you have a camera, again take a picture of each petri dish.
    2. Gently poke the moisturizer in each petri dish. Is it soft and cushiony, or is it hard? Is the moisturizer in some dishes cracked? Do some dishes look unchanged? Can you see the gelatin dessert below the moisturizer in some dishes?
    3. Use a toothpick to scrape away some of the moisturizer in each petri dish so you expose the gelatin dessert beneath it. Poke the gelatin dessert. Is it hard and firm, or is it soft? Try to arrange the petri dishes from hardest to softest gelatin dessert and record this order in your lab notebook.

Analyzing Your Results

In this part of the science project, you will analyze your results and determine which skin moisturizer worked the best and how this correlates with the moisturizer's ingredients. You will specifically determine the percentage of initial weight and JELL-O gelatin desert height of each petri dish over time and assess how the moisturizers changed in other ways.

1. In your lab notebook, create a data table like Table 3. You will calculate the percent of initial weight for each petri dish over time and record these values in this data table.

2. To calculate the percent of initial weight, first make the value at 0 hours be 100%, as shown in Table 3.
   1. This means that the initial weight of the petri dish with the gelatin dessert and skin moisturizer will be thought of as 100%.
3. Then, for all following time points for each dish, calculate their percentage of the 0 hours' weight and record these values.
   1. For example, if at 0 hours a petri dish weighed 84.5 grams and after three days it weighed 75.1 grams, you would record 88.9% for day 3 for this dish. (75.1 grams divided by 84.5 grams equals 0.889, which is 88.9%.) This means that after three days it only weighted 88.9% of what it weighted at 0 hours.
4. Next make a line graph of the data in this table. You can make a graph by hand or use a website like Create A Graph to make a graph on the computer and print it.
   1. Put the time (in days or hours) on the x-axis (the horizontal axis) and the percent of initial weight on the y-axis (the vertical axis).
   2. Make a different line for each petri dish.
      1. If you tested many different skin moisturizers, you may want to average your results from the three dishes for each skin moisturizer and graph the averages to save space on your graph.
5. Analyze your graph.
   1. Did some types of skin moisturizers consistently (between all three dishes tested) lose more weight than other types?
      1. If some dishes lost a lot of weight, did they lose about the same percentage each day, or was there a point after which they did not lose as much weight?
   2. Did some types not lose much weight at all?
   3. How do the samples compare to the controls (the gelatin dessert only dishes)?
6. In your lab notebook, create a data table like Table 3, but instead of "Percent of Initial Weight of Petri Dishes" label this one "Percent of Initial Height of the JELL-O Gelatin Dessert." Use Table 2 in your lab notebook to calculate the percent of initial height of the gelatin dessert for each dish over time and record these values in this new data table. Do this by repeating steps 2 and 3, but this time use the data from Table 2.
   1. For example, if a dish had an initial height of 1.4 cm and after three days it had a height of 1.0 cm, the percent of initial height would be 71.4% (1.0 cm divided by 1.4 cm equals 0.714, which is 71.4%).
7. Next, make a line graph of the data in this data table as you did in step 4. Put the petri dishes on the x-axis and the percent of initial height of the gelatin dessert on the y-axis.
8. Analyze your graph.
   1. Did some types of skin moisturizers consistently (between all three dishes tested) lose a greater percentage of their gelatin dessert height than other types?
      1. If some dishes lost a lot of height, did they lose about the same percentage each day, or was there a point after which they did not lose as much height?
   2. Did some types of skin moisturizer remain about the same height?
   3. How do the samples compare to the controls?
9. Now look at both of your graphs together and any other observations you made and see if you can draw some conclusions.
   1. Do your graphs agree with each other, giving similar results for each skin moisturizer over time? In other words, did a skin moisturizer that lost a lot of weight also lose a lot of height? Do the shapes of the lines on the graph for a given moisturizer look similar?
   2. Do the results from your graphs agree with your observations from step 11 in the preceding section about how soft or hard the gelatin dessert was in the different petri dishes at the end of the experiment?
   3. Based on your graphs and other observations, which skin moisturizer(s) performed the worst in your experiment? Which performed the best?
   4. Can you explain your results based on the ingredients in each skin moisturizer?
      1. Hint: You may want to re-read the Introduction in the Background tab.
      2. See if you can find correlations between how well the skin moisturizers performed and which skin moisturizer(s) lists mineral oil as the first or second ingredient, which lists glycerin as the second ingredient (after water), which lists glycerin as the fourth ingredient, which contains triethanolamine, and which contains 100% petroleum jelly. Do your results make sense to you?
      3. If your results seem surprising, see if any other ingredients in the moisturizer (especially the first three listed) might help explain your results.
   5. What do you think this tells you about which skin moisturizer would be best to use on dry skin? What about the ingredients that you would prefer having (or avoiding) in a moisturizer?
      1. To answer this, be sure to think about how the model you used in this science project is different from what it is trying to model. For example, think about how JELL-O gelatin dessert is different from dry human skin, how often people usually apply skin moisturizer to dry hands, how much they apply to their skin, etc.
      2. If a skin moisturizer performed better than others, are there reasons someone with dry skin might not want to use it anyway? For example, does it have other ingredients that a person might not want to put on their skin?