Student Work Sample #3
Investigating the Ultraviolet Blocking Potential of Various Lotions, Creams, and Oils
Problem: Which lotions, creams, and oils are most effective in blocking ultraviolet radiation?
Hypothesis: None of the lotions, creams, and oils will be effective in blocking ultraviolet radiation.
Background Information:
There are two types of ultraviolet radiation that can damage a person’s skin: UVB rays, which cause sunburns, and UVA rays, which cause wrinkling, leather, and other signs of aging produced by light. To protect skin from sunburns and from skin cancer, the best thing to use is sunblock. First developed for soldiers in WWII, sunblocks are products that protect the skin from the sun’s ultraviolet radiation. They come in a majority of different lotions, creams, and oils with a large span of SPFs. SPF, the Sunblock Protection Factor, measures the strength of the UVB protection, but does not tell anything about protection from UVA rays. Even though it has been found that sunscreen needs to be applied at least every hour and a half to two hours despite the SPF, the higher the SPF, the more protection from the sun in that time span.
Sunblocks work in two ways. Inorganic chemicals in the sunblock such as zinc oxide or titanium dioxide reflect or scatter the light so it goes away from the skin while organic chemicals (carbon based) such as avobenzone or oxybenzone absorb the ultraviolet rays in place of the skin absorbing them. Inorganic chemicals are better than organic chemicals because they block the ultraviolet rays instead of absorbing them. The majority of the people who use sunblock do not apply enough on. This means their skin will still be absorbing ultraviolet light. That paired with an organic chemical based sunblock can be more harmful than helpful, especially since the sunscreen breaks down as it absorbs the rays, making the sunblock less effective and needed to be applied more often. That is why sunscreens with inorganic chemicals are better for people to use. Many people will not use sunblocks with inorganic chemicals though, because they traditionally appear white on the skin. Visible light is either absorbed or reflected. Inorganic chemicals in sunblock produce scattered light, which will redirect from one cluster of molecules to another in. At some point the visible light will either go back the way it came (back scattering) or forwards (front scattering). When back scattering occurs, the light has all colors in the visible spectrum, making the light and the sunblock white to our eyes. That is why scientists have been focused on creating sunblocks with nanosized inorganic clusters. One of the positive things about nano sunscreens is that as the particles get smaller and smaller, less visible light is scattered. This makes the sunblock appear clearer, making it more likely for people to use it. Along with that, nano sunscreens are more effective than other sunscreens because of their high dispersion and high concentration. If a sunblock has a low concentration and a low dispersion the few clusters of chemicals will be highly ineffective since they are very close to each other which creates large gaps in the blockage of ultraviolet light. That is why a sunscreen with a high dispersion and concentration is so important. The high concentration will mean more particles to block the sun, and with a high dispersion, the particles will cover the whole area where the sunblock has been applied.
Overall sunblock is extremely important for the protection it offers to the skin. Every day your skin is exposed to UVB and UVA rays and while, very few products are available to protect you from UVA rays, it is important to at least protect the skin from UVB rays. The way to do that is through inorganic nano sunscreens. Their high concentration and dispersion paired with the fact that they reflect ultraviolet rays, makes them more effective than large cluster inorganic sunscreens and organic sunscreens.
Independent Variable: The lotions, creams, and oils are the independent variable.
Dependent Variable: The color of each disk after exposure to the UV light is the dependent variable.
Control Variables: The starting color of the disks, the type of camera used, the time under the ultraviolet light, and the time between the disks being taken out from under the light and when the photo is taken are the control variables in the experiment.
Materials List:Plastic vialsDifferent lotions, creams, and oils
Well PlateNine UV sensitive disks of same color
UV lampQ-tips (Four for each trial done)
StopwatchCamera
Advanced Digital Imaging Software
Procedure:1. Pre-prepare the various lotions, creams, and oils in different vials, making sure to label the vials A-H.
2. Gather all of the materials, including the pre-prepared vials of lotion.
3. Making sure that the lighting is good, prepare the camera to take a photo.
4. Place the nine disks in the slots in the well plate.
5. Coat each disk, except for the control, with a different test lotion using an unused end of a Q-tip. Make sure that each disk has a thin and equal layer of lotion, cream, or oil. Also make sure to take note of which slot holds which samples and control disk.
6. Then place the well plate under the UV lamp, making sure that the well plate is centered in the middle of the light. Using the stopwatch keep the well plate under the lamp for exactly one minute.
7. When the minute has ended, take the well plate out front under the UV light, bring it over to the camera, and get ready to take a photo of the well plate. While doing this use the stopwatch to time fifteen seconds since the well plate was taken out from under the UV lamp and right when fifteen seconds have passed, take the photo of the well plate.
8. Then using the photo, rank the samples from least to most effective.
9. Next do at least two more trials to collect more data, making sure to wash the well plate and the disks between each trial.
10. Finally using Advanced Digital Imaging, take a closer look at each photo and check the rankings of the samples.
11. Then still using the ADI software, find the percent red, green, and blue of the pixels, using 200 (+/-10) pixels.
Results:
Rankings
Rank(Least Effective to Most Effective) / Trial 1 / Trial 2 / Trial 3
1 / Control / Control / Control
2 / H / H / H
3 / F / F / F
4 / E / E / E
5 / A / A / A
6 / B / B / B
7 / G / G / G
8 / D / D / D
9 / C / C / C
Layout of Disks in both Pictures
- / - / - / -- / - / - / Control
H / G / F / E
D / C / B / A
Trial 1
Trial 1 Pixel Rankings
Rank / # of Pixels / Red % / Green % / Blue %Control / 196.0 / 54.51 / 31.76 / 33.33
H / 196.0 / 98.59 / 40.97 / 56.47
F / 195.0 / 1.92 / 35.86 / 56.86
E / 195.0 / 60.0 / 51.76 / 40.39
A / 196.0 / 12.16 / 37.65 / 56.08
B / 196.0 / 62.35 / 54.9 / 41.96
G / 196.0 / 64.71 / 58.4 / 43.92
D / 196.0 / 62.35 / 55.29 / 43.92
C / 196.0 / 60.0 / 54.9 / 39.61
Trial 2
Trial 2 Pixel Rankings
Rank / # Pixels / Red % / Green % / Blue %Control / 195.0 / 54.9 / 32.94 / 42.61
H / 195.0 / 54.9 / 32.94 / 41.96
F / 195.0 / 56.47 / 36.47 / 42.75
E / 195.0 / 57.25 / 41.96 / 47.97
A / 195.0 / 56.8 / 47.45 / 45.49
B / 195.0 / 57.65 / 49.8 / 47.45
G / 195.0 / 65.49 / 62.75 / 56.08
D / 195.0 / 55.29 / 52.94 / 56.73
C / 195.0 / 59.61 / 56.08 / 50.98
*Could not find photo from Trial 3 when it came time to do use the ADI software.
Discussion: Based on the experiment, the lotion, cream, or oil that was the most effective was Sample C, while Sample H was the least effective. Sample C had little color change after one minute and was the closest to being the same as it was before being put under the UV lamp. Sample H was the exact opposite. It was only a shade or two lighter than the control disk, meaning that the lotion, cream or oil was highly ineffective. Samples A-D were all extremely close to each other in color and samples H and F were very alike. What was surprising was Sample G. On the surface it looks highly effective because all that can be seen is the white lotion, oil, or cream that is the sample, but underneath Sample G was almost as dark a pink as sample F. So while Sample G looked effective, it is extremely ineffective. This could have caused an issue with the ranking since it was very unclear just how dark of a pink Sample G was underneath the white lotion, cream, or oil.
The information that was gathered from the ADI software was too varied to be of any use, especially since the photo from Trial 3 could not be found. It seems that in Trial 2 the percentages of red, green, and blue increased for the most part, but since there were anomalies within the Trail 2 image (random drops and raises) and since the Trial 1 data has extreme drops and jumps with no consistent pattern, no conclusion can be drawn from that information.
There are a few possible issues with the experiment, the first being the lighting in the photos. Since the lighting is not very good, it was hard to see the differences between colors in Samples A-D. This could mean that the ranking of those samples is wrong. To solve that we could have put the well plate with the samples under the UV light for one minute, taken the plate out and ranked them then and there. Then we could have waited for the color to have faded from the samples, put the well plate back under for one minute and then take the photo, That way not only would the photo match the results, but we would have been more accurate in the rankings of the samples. The other issue that came up was in coating the well plates. The various lotions, creams, and oils were all of different consistencies which made it hard to make sure each well plate was coated evenly. This could have been solved in a couple of different ways; possibly by soaking the disks in the samples for the same amount of time or finding samples of the same consistency.
Overall the hypothesis that “none of the lotions, creams, and oils will be effective in blocking ultraviolet radiation” was incorrect. Samples A-D were all highly effective in blocking the ultraviolet radiation which can be seen through the fact that they, for the most part, are a whitish-pink color. To continue testing this and improving on the hypothesis we could continue to do more trials with longer periods of time to see which lotion, cream, or oil is more effective over a long period of time. Sunblocks and other products that protect skin from UV light are most often used when someone knows that they will be outside for a long time. One minute, while showing which is more effective, is not realistic compared to how long people stay outside. If the time had increased from one to three to five to ten to even thirty minutes, the lab would have given us results that are more practical and useful in seeing how effective the lotions, creams, and oils were in protecting the disks from the ultraviolet rays.
Bibliography
Grifantini, Kristina. "How Does Sunscreen Work?" LiveScience. TechMedia Network, 25 June 2010. Web. 09 May 2016.
"Clear Sunscreen: How Light Interacts with Matter." NanoSense : Activities. SRI International, 1 May 2008. Web. 12 May 2016.
"Sunscreens Explained." Sunscreens Explained. The Skin Cancer Foundation, 22 May 2012. Web. 09 May 2016.