DIY sunscreens are becoming popular but some of the ingredients have not to be investigated and considered to protect against harmful sun radiations. Besides, they could be less effective than the available commercial sunscreens and the available studies have not much for FDA to approve them. Therefore, it would be imperative to test them to establish their level of efficacy. This would be a basis of reliable information for those preferring to use the DIY sunscreens to commercial ones as well as adding to the data as a ground for FDA the DIY sunscreens that would emerge to be safe.
Literature Review
In recent years, the level of Ultraviolet (UV) radiation reaching the earth has dramatically increased owing to the destruction of the ozone layer by greenhouse gases. This has led to the overexposure of the skin to UV radiation, which contributes to skin-related disorders in humans. UB radiation is divided into UVA, UVB, and UVC based on the wavelength of the radiation (Saewan and Jimtaisong, 2015). UVB is the most potent radiation that causes skin disorders including photoaging, immunosuppression, sunburn cells, hyperpigmentation, edema, skin cancer, and erythema (Saewan and Jimtaisong, 2015). Sunscreen products are applied on the skin to block the UV radiations from penetrating the epidermis.
Sunscreens were originally developed to reduce sunburns (erythema) emerging from UVB radiations. As a result, erythema has been the endpoint in measuring the efficacy of sunscreens, commonly known as sunscreen protection factor (SPF) (Young, Claveau, and Rossi, 2017). SPF is computed as the ratio of the dose of solar radiation causing erythema with sunscreen applied to when sunscreen is not applied (Young, Claveau, and Rossi, 2017). The regulatory standards for sunscreens significantly differ across the globe; in the United States, the products are referred to as over-the-counter drugs. The FDA SPF is similar to that of ISO 24444, which is a globally accepted efficacy standard for sunscreens.
It has been known that upon penetration into the skin epidermis, UV radiation is directly absorbed by DNA causing the formation of pyrimidine dimers. There is a DNA repair mechanism for this type of damage that removes the dimers and adds the correct sequences. However, this repair mechanism fails at times leading to permanent DNA mutations (Paul, 2019). Luckily, sunscreens protect against such damage, and in vivo testing of the sunscreens demonstrates this. Yet, not all sunscreens are effective at doing this and could contain harmful chemicals as postulated by Paul (2019).
According to Li et al., (2019), UVA and UVB protective sunscreens should have an SPF of at least 30 or even higher. The researchers advise that patients ought to be educated regarding the mode of application as well as other crucial factors regarding the use of sunscreens apart from SPF values. They recommend the use of water in oil emulsion as the base for sunscreens application to harness SPF values and promote water resistance (Li et al., 2019). However, patients prefer oil in water as their sunscreen vehicle because of its noncomedogenic properties and lighter feel at the cost of effective protection.
While there are commercial sunscreens whose efficacy in protecting against radiations has been tested and proven, the shift towards natural cosmetics has prompted people to develop homemade protection sunscreens, typically known as DIY sunscreens (Garcia, 2019). Commercial sunscreens undergo rigorous testing to prove their efficacy before being approved for sale. The Skin Cancer Foundation advocates that sunscreen manufactures adhere to the guidelines of the Food and Drug Administration when testing their products to prove their claim on the labels (Garcia, 2019). Unfortunately, this is not the case for homemade sunscreens and their efficacy can barely be ascertained.
The allure of these homemade sunscreens is also rooted in the need to cut costs and the belief that natural creams with home-picked ingredients are healthier than commercial sunscreens whose ingredient lists are chemicals with names that are barely legible. In a study done on Pinterest regarding the popularity of DIY sunscreens, it emerged that 95.2 percent of the saved posts regarded the sunscreens to be effective (Cohut & D’Emilio, 2019). However, 68.3 percent of the promoted DIY sunscreens lacked appropriate protection against UV radiation (Cohut & D’Emilio, 2019). Besides, the promotion posts of the homemade sunscreens failed to give specific SPF values of the recipes, giving an approximation of anywhere between 2 and 50 (Cohut & D’Emilio, 2019). This is contrary to the recommendations of the American Academy of Dermatology for use of broad-spectrum sunscreens with an SPF of 30 or higher.
Testing the recipes that are popular in homemade sunscreens will go a long way to establishing their protection capability and foster the safety of people from UV radiation. Yeast, Saccharomyces cerevisiae, would be an appropriate candidate for in vitro testing owing to their genetic resemblance to mammals (Botstein, Chervitz, and Cherry, 1997). Their genes encode several proteins that are similar to human proteins with nearly 31 percent of the protein-encoding genes in yeasts having homologs in human protein sequences (Botstein, Chervitz, and Cherry, 1997). Therefore, using yeast as the testing model for the DIY sunscreens and comparing their efficacy with commercial sunscreens will shed light on the safety and efficacy of the homemade recipes.
In both experiments, yeast cells Saccharomyces cerevisiae was used to determine how effective two different DIY recipes are in protecting the cells from UV radiation and how important of a role each individual ingredient plays while mixed with the base. Both experiments were prepared the same aside from replacing the lotion base from the original experiment with a coconut oil base. For the original experiment, 4 controls were set up along with 5 different sunscreen recipes. The 5 sunscreen treatments included: Zinc Oxide + Lotion, Carrot Seed Oil + Lotion, Jojoba Oil + Lotion, Raspberry Oil + Lotion, and DIY recipe (contains the lotion + all the individual ingredients). The 4 controls set up for this experiment include No UV exposure plate to represent the approximate number of cells plated, a commercial sunscreen plate to compare the results with the DIY recipe plate, no sunscreen plate to record how many cells UV will destroy in 2 minutes, and a lotion only plate to ensure that some light got through the thick white layer on top of the saran wrap. The yeast cells had to be diluted to 10^-6 before being plated and then the saran wrap with each treatment spread across was then wrapped carefully on the plate making sure the saran wrap did not sink and touch the plated cells. The plates following a 2-minute exposure to UV radiation were then stored at normal room temperature. After 96 hours, the number of colonies that grew on each plate was counted and recorded.
For the follow-up experiment, there were 2 controls: no UV exposure plate and only a coconut oil plate. All 5 sunscreen treatments for this experiment were made in the same proportion and order with the exception that coconut oil was used instead of lotion. This allowed us to test the difference between using lotion as a base in the first experiment compared to a thin base such as coconut oil. The same procedural steps apply to this experiment.
The proportion of survivors was then calculated for each plate but dividing the number of colonies counted by the number of cells plated (the no UV plate).
Results and Conclusion
The SPF protection products used in the experiment include commercial sunscreen, lotion, raspberry oil, carrot seed oil, zinc oxide, jojoba oil, and DIY sunscreen. Among these products used in the experiment, DIY sunscreen had the lowest protection efficacy with the proportion of survivors upon exposure to UV radiation being 0.57. The lotion had 1.08, which was the highest proportion of survivors. Comparison of commercial sunscreens to DIY sunscreens shows that commercial ones are better with the proportion of survivors being 0.84 compared to 0.57 for DIY sunscreen as shown in figure 1. The average proportion of survivors for lotion, raspberry oil, carrot seed oil, and jojoba oil is higher than that of commercial and DIY sunscreens.
A t-test to compare the significance in the difference of efficacy for the various protections showed that none of them was significant. This is shown in appendix 3. However, follow-up experiments with a different base (coconut oil) gave different results.
In the follow-up experiments, the use of lotion a base, which is thick was replaced by coconut oil, which is a thin base. It became worse for DIY sunscreen when using this base as the survival rates dropped to 0.11. Other protective products significantly lost their efficacy when using the base as shown in figure 2. However, a comparison of the efficacy of the various protective products in a t-test showed no significant difference as shown in appendix 4.
Comparison of the original experiment to the follow-up experiment where a different base was used indicated significant differences in efficacy. An analysis of the p-value from the t-test showed that the efficacy of DIY oil was significantly different from that of commercial sunscreen with a p-value of 0.05. However, the efficacy of DIY oil was not significantly different from that of DIY lotion as seen from the p-value of 0.23. Other products including carrot seed, raspberry, jojoba, and zinc oxide showed a significant difference in efficacy when different bases were used as shown in appendix 5. The cost of making 500 mL of a DIY from the products used in the experiment has been outlined in figure 3.
Figures
Figure 1. The proportion of surviving S. cerevisiae cells following a 2-minute exposure to UV radiation while covered in various types of SPF protection with lotion as a base. After being exposed to the UV light, the protective saran wrap containing the sunscreen was removed, petri dishes were stored at room temperature and the formed colonies were then counted after 96 hours. There are four controls present in this experiment: no UV, UV and no sunscreen, commercial sunscreen, and lotion only. Proportion of survivors was calculated by dividing the colonies counted in the various treatment by the number of colonies counted under no UV light. The commercial sunscreen compared to the DIY recipe obtained a p value of 0.39 (>0.05, not significant). The use of the DIY sunscreen versus the commercial sunscreen did not present an effective difference. Each data point in the graph above is the average of 3 replicates and the error bars represent the standard deviation.
Figure 2. The proportion of surviving S. cerevisiae cells following a 2-minute exposure to UV radiation while covered in various types of SPF protection with coconut oil as a base. The protective sunscreen layer was removed, and the proportion of survivors was calculated by dividing the number of colonies grown by the number of cells plated (no UV exposure plate) after 96 hours. Zinc oxide is the only individual ingredient mixed with coconut oil that yielded the highest proportion of survivors. The effectiveness between just the zinc oxide and the DIY sunscreen is shown to be insignificant (p-value= 0.7964; p>0.05). The use of zinc oxide provides more protection from the UV radiation than any of the other components in the DIY recipe. Each data point is the average of 2 replicates and the error bars represent standard deviation.
Figure 3. The estimated cost of the most effective DIY sunscreen.
Limitations
The experimental design could be improved to check the safety of the products used as DIY sunscreens. In the experiment, only the efficacy of the products was assessed while the problem statement authenticated the need to also test the safety of the products. This would involve establishing the active ingredients in the DIY sunscreens and their health safety for human use.
Besides, the number of replicates may not have been enough to establish the efficacy of the DIY sunscreens. The variation could emerge in the amount of lotion or oil used as the base for sunscreen application. Slight variations in quantities could give different results, which would lead to a false conclusion about the safety and efficiency of the given product. Besides, such variations would cause the experimenter to commit type II error in the t-test i.e. concluding the difference is not significant when it is significant.
While S. cerevisiae is appropriate for use as models to test the sunscreens, they may not accurately give results as they would occur in humans. Some of the tested sunscreens could be more or less efficient in humans contrary to the results provided by the use of yeast cells. Besides, the mechanism of damage to the yeast cells from the UV radiation could be different from the way the radiations affect humans.
Summary and Recommendations
The use of yeast cells to test the SPF of the various homemade sunscreens as well as the commercial sunscreen gave a clear picture on which would provide appropriate protection. DIY sunscreens were not better than commercial sunscreens with the proportion of yeast cells that survived being 0.57 compared to the 0.84 for commercial sunscreens. However, other products such as raspberry, carrot seed, zinc oxide, and jojoba oil performed better than commercial sunscreens. Regardless, a t-test to establish the significance in the difference of their efficacy indicated no significant difference in the products provided. The difference became significant when the lotion base was replaced by coconut oil, indicating that lotion conferred a better protective ability for the sunscreens.
Based on the findings of this experimental study, DIY sunscreens do not confer better protection from UV radiations than commercial sunscreens. They perform worse when a thin base such as coconut oil is used. Therefore, this confirms the postulate in the problem statement that the DIY sunscreens are not better than commercial ones, which would be recommended as their safety could be guaranteed from the rigorous testing done before putting them for sale. This type of testing is absent in DIY sunscreens yet they do not confer a higher SPF value.
Follow Up Work
Follow-up work should involve establishing why there is such a significant difference in the efficacy of the sunscreens when bases of different thicknesses are used. Perhaps, this could be compensated by the thickness of the sunscreen being applied or even the application frequency. While using a thickness of 2 mg/cm2 is recommended, natural applications usually are in the range of 0.39 to 1.0 mg/cm2 (Petersen & Wulf, 2014). It would be imperative to check the extent that this discrepancy affects the SPF of sunscreens. Petersen and Wulf (2014) indicated that the use of sunscreens with very high SPF or early reapplication may compensate for the difference in the amount of sunscreen applied during testing and in reality.
The goal of this follow will be to establish the appropriate thickness of sunscreen application for each of the given sunscreens whether homemade or commercial. This would then be used to promote an appropriate application for effective protection from the harmful sun rays. The experiment would also establish the appropriate frequency of application so that people who may opt to continue with the DIY sunscreens may have firsthand information regarding application thickness and frequency. Besides, the various sunscreens may need different application thicknesses and frequencies and this may be probed in follow-up experiments.
The expected outcomes will be that some of the products with high SPF values would need a lower application thickness to confer the same level of protection as those with low SPF values. Also, the appropriate frequency of application will vary depending on the SPF value. The type of bases will impact the thickness required for each of the sunscreens as seen from those used in the previous experiment.
Another thing to consider in follow-up experiments would be to establish the active elements in the DIY sunscreens and their safety for skin application since their SPF has always been tested. While some products demonstrate significant SPF values, they may have other compounds that could pose health risks to humans. Also, they may confer other health benefits apart from UV radiation protection. For instance, apart from being a potent sunscreen, jojoba oil has antibacterial properties. While it does not protect against all bacterial infections, it is potent for Salmonella, E. coli, and Candida. Besides, its similarity to sebum makes it unlikely to clog skin pores leading to fewer breakouts and acne. others like carrot seed oil have anti-aging properties.
The goal of such an experiment would be to establish health hazards associated with the DIY sunscreens as well as the additional benefits linked to them apart from SPF. Some of the yeast cells may not have died of being exposed to UV radiation but could have resulted from some compounds in the sunscreens. Therefore, culturing the yeast cells upon application of sunscreens would ensure that the safety of the products is ascertained. Such an experiment would go a long way to enhancing the use of sunscreens as well as the discernment on which are safe and appropriate for use for an individual depending on their skin tone and moisture content level.
Appendix
Appendix 1
Appendix 2
Appendix 3
Appendix 4
Appendix 5
