The Effect of Sunscreen SPFs on UVA and UVB Rays

By Sarah

Energy and Material Sciences

Abstract

The purpose of this investigation is to prove which sunscreen SPF (sun protection factor) works most efficiently with blocking UV rays. It was estimated that the 5 chosen SPFs (15,30,50,70 and 100) would all work very similarly, with 100 possibly being the highest. This was tested by applying 10 milligrams of sunscreen to a transparency sheet and (using a UV light) recording the UV light (sensed by UVA and UVB sensors) sensed before and after. Three trials were performed. The percent of UV light blocked by the sunscreen was then calculated. The three trials of each 5 SPFs and UVA and UVB (a total of 30 trials) were then analyzed and it was found that the hypothesis was supported.

Application

Learning about how sunscreen works and how to protect skin from the harmful rays of the sun is very important due to all of the consequences. People do not understand the risks involved in not wearing sunscreen, not wearing sunscreen properly, etc. This is all due to the statistics that 1 in 5 Americans develop skin cancer by age 70 and skin cancer is the most common cancer (Skin Cancer Foundation, n.d.). According to a study done in 2009 by Leslie K. Dennis, most people think that getting tan and producing melanin is a good thing and makes you more attractive to society when in reality all it is is skin that was damaged preparing for more damage. Another reason why it is important to learn about how sunscreen is because society does not realise that SPF does not mean the strength of the sunscreen. Therefore, they are lead to believe that which is just false.

Research

• UVA rays (320–400 nanometers [nm]) have a longer wavelength than UVB rays (280–320 nm).
• UVB rays cause sunburns and UVA rays cause damage to the structure of the skin (wrinkles) but both can lead to skin cancer.
• Skin cancer forms as a result of built up damage from UV rays.
• Sunscreen helps prevent harmful UV rays from reaching skin by absorbing the rays and slowly releasing them as heat.
• Sunscreen is made up of organic chemical compounds containing covalent bonds.
• The sunscreen SPF (Sun Protection Factor) is the amount of times longer it takes for UVB rays to penetrate through the skin and cause a sunburn compared to when there is no sunscreen applied (calculated by dividing the amount of UV radiation needed to affect the skin with sunscreen divided by the amount of UV radiation needed to affect the skin without sunscreen).
• Sunblock provides pigmented minerals such as zinc oxide to give physical shield.
• A chemical change occurs when the skin gets damaged. A type of DNA lesion occurs where it is a covalently bonded complex of two adjacent thymines on a single strand of DNA.
• Melanin is released when the DNA is damaged to help protect the skin in the future. Melanin is made in cells called melanosomes, which live in melanocytes.
• 3 types of melanin- eumelanin (a brown/ black pigment in hair and skin, protects the most against DNA damage from radiation), neuromelanin (only found in the brain) and pheomelanin (an orange to red pigment used in the hair and skin, protects the least)

Procedure

A transparency sheet was laid over the UV sensor and under the UV lamp and the “before sunscreen” value was recorded. 10 mg of the appropriate sunscreen was weighed and place on the sheet using a cotton swab. The sunscreen then dried and the “after application/absorption” value was recorded. This process was repeated for the 5 SPFs and the 2 UV types.

Conclusions/results

Based on the results of the experiment, it can be concluded that the sunscreen used in the procedure did not work very effectively or sunscreen does not do well in blocking out UVA rays. However, the data states that all of the SPFs worked pretty much the same. This means that the hypothesis is semi-supported because all of the SPFs technically worked about the same, but something was off about the UVA part. The original hypothesis was that the SPFs would all work similarly. It is clearly seen that in both sets of data the SPFs worked very similarly, but when analyzed with a 2-Way Anova test (see Figure 1), there was definitely a difference in the results with SPF 15/30 and SPF 70/100. SPF 50 could not be analyzed because the analysis was not applicable for 5 rows. All in all, typically the higher you go in SPF the more effective the sunscreen works to block UV rays.

Figure 1

Conclusions/results graphs(continued)

Graph used for 2-Way Anova Test

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Discussion

• The 5 SPFs that were tested all worked very similarly just like it was predicted
• Based on the statistical 2-way Anova test, there was a definite difference between SPF 15/30 and SPF 70/100
• It might seem like sometimes higher SPFs work just as good (if not worse) than lower ones because of a false sense of security. Consumers tend to rely on high SPFs to the point where they might not re-apply or use the recommended amount.
• Even though the UVA data was so unexpected, it did not technically disrupt the hypothesis from being supported. UVA rays have a longer wavelength than UVB rays, so maybe the sunscreen did not work as well in that case
• There was not a way to be more precise because of the models of equipment available, but because there was a difference (based on the 2-Way Anova test)

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