For athletes who face intense sun exposure and sweat conditions, sunscreen development requires careful formulation to achieve effective protection, durability, and a cosmetically elegant feel.
AdobeStock by C Malambo/peopleimages.com
I am Nikita Gill, a high school cross country and track runner and budding chemist. I am driven by a deep curiosity about using my scientific background to solve everyday problems. One area where this intersection becomes crucial is in SPF (sun protection factor) products. Athletes, especially those who spend hours training outdoors, need reliable sunscreen to shield their skin from harmful UV (ultraviolet) radiation. So far, all sunscreens available were chemical-based SPFs or thick, uncomfortable mineral SPF products. So, this sent me on a path to create the first non-chemical, thin, easy-to-apply SPF sunscreen for athletes.Jocelyn Manfut (left) and Nikita Gill (right)Sun Deep Cosmetics
Chemical vs. Mineral Sunscreens: Finding the Right SPF for Athletes
Chemical sunscreens, widely available and commonly used, have several significant downsides for athletes. For one, chemical SPF often leads to an uncomfortable stinging sensation when sweat causes it to run into the eyes during intense activity. Eye stinging can be a significant distraction when competing or training, especially when visibility is key to performance. Beyond personal discomfort, chemical sunscreens have a broader environmental impact that is increasingly hard to ignore. Research shows that chemical UV filters, such as oxybenzone, destroy coral reefs, pollute oceans, and harm marine life, making them a poor choice for swimmers, surfers, and triathletes interacting directly with aquatic environments (Olson, 2022). Furthermore, some chemical filters have been linked to hormone-disrupting effects, raising concerns about their safety, particularly for teenagers and young adults who are still in critical stages of growth and development (Suh, 2020).
In response to the issues associated with chemical sunscreens, many people have turned to mineral-based options, which use zinc oxide as their active ingredient. Zinc oxide provides broad-spectrum UV protection and is safer for human health and the environment (Adams, 2022). However, current zinc oxide formulations are not without their drawbacks. Most zinc oxide-based sunscreens are notorious for their thick, pasty texture, which makes them difficult to apply evenly. Athletes need a product that feels light and comfortable, almost like makeup, yet many options leave a heavy, sticky residue on the skin or, worse, the white cast. This noticeable white cast can deter people from using them regularly (Adams, 2022). Additionally, some of these products contain other toxic ingredients harmful to developing bodies, which contradicts the intention of using a safer alternative to chemical SPF.
Mineral sunscreens, containing active ingredients like zinc oxide and titanium dioxide, form a physical barrier on the skin's surface that reflects and scatters UV rays, preventing them from penetrating the skin (Adams, 2022). In contrast, chemical sunscreens use organic compounds that absorb UV radiation, converting it into heat, which is then released from the skin. Mineral sunscreens are often recommended for individuals with sensitive skin, as they are less likely to cause skin irritation. However, they can sometimes leave a visible white residue on the skin. Conversely, chemical sunscreens are more transparent upon application but may cause skin reactions in some individuals. Both types can provide effective sun protection; the choice between them depends on personal skin type and cosmetic preferences (Adams, 2022).
From speaking to experts, there are several aspects to creating an emulsion such as this. The first is determining the proper active ingredient grade to use. In this case, zinc oxide comes in many different types of particle sizes and coatings (Sayer, 1990). The next aspect is to choose the proper diluent. In this case, a diluent is the solvent that suspends the particles, so it aids in better spreadability and feel. Another aspect is the emulsification process; using improper emulsifiers will cause the emulsion to separate, meaning that the oil and the water will not be in a homogeneous system. This would cause the SPF to exhibit a lower value than normal as the active is not equally spread (Greenwald, 1955). Other aspects include preservation and active ingredients for marketing cases (Greenwald, 1955).
Developing a High-Performance Zinc Oxide Sunscreen for Active Lifestyles
Recognizing these issues, I decided to leverage my chemistry background and create a new type of zinc oxide sunscreen specifically designed for active individuals who demand superior protection and a cosmetically elegant finish. To ensure the highest quality product, I researched various zinc oxide suppliers extensively to find the most suitable active ingredient. After careful consideration, I identified three key suppliers, Kobo, BASF and Evercare, using the popular online database UL Prospector. Kobo offers pre-made dispersions that are convenient to use, but unfortunately, they include objectionable ingredients and excipients that make them a less-than-ideal option (Sayer, 1990). BASF's Z-Cote, while providing a good source of zinc oxide, cannot finely control particle size, which is critical for achieving transparency on the skin. Ultimately, Evercare emerged as the best choice (Gowell, 2015). Their Zano 20 product offers the optimal combination of high broad-spectrum UV protection and excellent transparency. Zano 20 is also Ecocert and COSMOS approved, aligning with the growing demand for eco-friendly and ethically produced cosmetic ingredients (Evercare, 2024).
For athletes who face intense sun exposure and sweat conditions, sunscreen development requires careful formulation to achieve effective protection, durability, and a cosmetically elegant feel (Gowell, 2015). Zinc oxide, known for its broad-spectrum UV protection, forms the cornerstone of many mineral-based sunscreens. However, its naturally dry and chalky texture poses unique formulation challenges. I felt it was necessary to explore the selection of optimal diluents to enhance zinc oxide spreadability. Also, since this product direction is for athletes, the importance of water-resistant agents and the selection of emulsifiers are important to the overall product.
Perfecting the Feel of the Sunscreen
Zinc oxide is a UV-protective mineral with a high refractive index that is ideal for shielding skin against UVA and UVB rays. However, its powdery nature and large particle size contribute to a dry and chalky feel, making it difficult to apply evenly on the skin (Vujovic, 2015). This lack of spreadability affects user experience and can also reduce SPF effectiveness since uneven application leaves gaps in coverage. A factor called agglomeration causes the individual zinc particles to group together and allow patches where UV light can directly affect the skin (Vujovic, 2015). So, in designing the delivery system, it is imperative to avoid any chance of agglomeration.
For athletes, sweat and water exposure are routine, yet sunscreen efficacy decreases when exposed to moisture.AdobeStock By AntonioguillemThe ideal diluent for a zinc oxide formulation must improve spreadability, reduce the dry feel, and contribute to a stable suspension, ensuring that zinc oxide particles remain evenly distributed (Kaur, 2014). I selected C12-15 alkyl benzoate and dicaprylyl carbonate. These were chosen as diluents for this formulation because they enhance spreadability and have favorable cosmetic properties. Upon dry skin application, both of these gave adequate lubricity and spreadability without a major oily cast (IFSCC, 1997).
C12-15 alkyl benzoate is widely used in cosmetics as an emollient and spreading agent. It provides a silky texture and light, non-greasy feel, making it ideal for an athlete-focused sunscreen that needs to remain comfortable on the skin during physical activity. Its effectiveness as a spreading agent enhances the uniformity of zinc oxide particles on the skin, which in turn can improve the sunscreen's SPF (Abou-Dahech, 2020). Dicaprylyl carbonate offers a similarly favorable spreadability and adds a light, smooth skin feel without the heaviness often associated with mineral sunscreens. Its rapid absorption rate reduces greasy residue, which is especially advantageous for athletes who rely on quick absorption to prevent slippage and maintain comfort during performance (Abou-Dahech,2020). Combining these diluents provides a balance of good spreadability and a cosmetically elegant finish, critical for creating a light yet effective sunscreen. For athletes, sweat and water exposure are routine, yet sunscreen efficacy decreases when exposed to moisture.
A water-resistant agent ensures the product remains effective despite sweating and environmental conditions. Waterproofing agents create a film on the skin that holds the active ingredients in place, even as the user perspires or engages in water-related activities (Kaur, 2014). Without such agents, the zinc oxide and other sunscreen ingredients may wear off prematurely, reducing their protective abilities and increasing the risk of sunburn and UV damage. Polyester-7 (and) neopentyl glycol diheptanoate is a polymer that forms a durable film, effectively locking in the active ingredients (Fevola, 2017). These agents ensure that the zinc oxide particles remain adhered to the skin's surface for longer, offering continuous UV protection even during intense sweating. Its film-forming properties make it ideal for athletic sunscreens as it combines durability with flexibility, adapting to the body's movements. Hydrogenated methyl abietate is another water-resistant agent that complements the film-forming effects of polyester-7 (Kaur, 2014). It provides an additional layer of protection and reinforces the adherence of the active ingredients. Hydrogenated methyl abietate contributes to the formulation's longevity and effectiveness by creating a resilient barrier on the skin.
The Spreadability of Sunscreen
In a sunscreen formulation, emulsifiers play a key role in stabilizing the product by ensuring that oil and water components remain mixed. This is incredibly challenging in zinc oxide-based sunscreens, as zinc oxide particles tend to clump, which can cause uneven distribution and decrease SPF effectiveness (Fevola, 2017). Effective emulsifiers help to disperse these particles evenly and maintain stability over time. Polyglyceryl-10 stearate is a highly effective emulsifier that provides excellent stability in zinc oxide formulations (Fiume, 2023). It helps to create a uniform suspension, ensuring that each application delivers consistent UV protection (Fevola, 2017). It is also mild and non-irritating, ideal for athletic users with sensitive skin due to frequent sun exposure. Sorbitan sesquioleate functions as an additional stabilizing agent, particularly beneficial for high SPF products where maintaining uniformity of active ingredients is essential. It also enhances the product's spreadability, making it easier for athletes to apply (Abou-Dahech, 2020). Polyglyceryl-2 dipolyhydroxystearate is a versatile emulsifier that supports stable emulsion formation while contributing to a smooth texture (Fiume, 2023). Its effectiveness in suspending zinc oxide particles ensures that the sunscreen remains effective, comfortable, and visually appealing. Combining these emulsifiers addresses the challenge of creating a stable, spreadable sunscreen that remains effective and pleasant to use, regardless of environmental conditions.
Balancing in vitro and in vivo Testing for Accurate Sunscreen Efficacy Results
SPF boosters are added to sunscreen formulations to enhance the efficacy of UV-blocking ingredients without increasing the concentration of active ingredients (Wong, 2022). For athletes who require high SPF levels to protect against prolonged sun exposure, SPF boosters can provide the additional protection needed while maintaining a lightweight, non-greasy formulation. Tridecyl salicylate is an SPF booster that enhances UV protection by increasing the efficiency of zinc oxide's UV-blocking abilities (Wong, 2022). It also contributes a soft, emollient texture that complements the light feel of the diluents used. This booster aids in achieving higher SPF values without compromising the formulation's spreadability or elegance. Butyloctyl salicylate is another booster that increases SPF while providing a non-greasy finish. Known for its compatibility with other sunscreen ingredients, butyloctyl salicylate contributes to the product's effectiveness in outdoor conditions while maintaining a comfortable feel on the skin, which is ideal for prolonged athletic activity (Wong, 2022).
Adding proper preservative systems is imperative to ensure minimal microbial contamination in this product. This case will be using a well-known preservative called Spectrastat G2. It is ideal due to its usage in many natural products and its broad spectrum coverage. The general usage of spectrastat G2 is one percent; this, coupled with a chelating agent that sequesters ions, will help aid the preservation system. In this case, I used sodium phytate at 0.1% (Behrens, 2021). The product will undergo accelerated stability testing, which will undergo high heat for three months, with a series of tests afterward to ensure it will appear reasonably similar to the original product (21 CFR § 211, 2024).
Regarding SPF validation, it's important to realize that the actual SPF number is derived through various tests. Some are in vivo, and some are in vitro, meaning that some can be done on an artificial substrate and some must be done on an actual human subject. Testing must be done on an actual person to validate and closely assign an SPF number in the United States (21 CFR § 352, 2024). However, in other countries, such as Europe, testing on artificial substrates is allowed. In my test, for the purposes of the initial rd of this sunscreen, I could not immediately test as I needed sponsorship from a contract manufacturer to conduct any third-party studies. So, I utilized a UV spectrometer made by the company Lab Sphere. This device helps approximate the SPF value and the broad-spectrum ability of the sunscreen (Pelizzo, 2012).
UV Protection of Sunscreen
In sunscreen, the product can absorb or block various wavelengths of UV light. UV light is categorized into UVA, UVB, and UVC based on wavelength and energy. UVA 320-400 nm penetrates deep into the skin, causing premature aging and contributing to skin cancer. UVB 280-320 nm, affects the outer layers of skin, leading to sunburn and playing a key role in skin cancer development (Luzuriaga, 2022). UVC 100-280 nm, is the most dangerous but is absorbed by the ozone layer and doesn't reach Earth. SPF, or sun protection factor, measures protection primarily against UVB rays, as they are the primary cause of sunburn and direct DNA damage. Broad-spectrum sunscreens protect against both UVA and UVB, but no SPF rating accounts for UVC as it doesn't naturally reach the skin (Luzuriaga, 2022).
An ultraviolet spectrometer can analyze a sunscreen's sun protection factor (SPF) by measuring its ability to absorb or block UV radiation, particularly in the UVB (290–320 nm) and UVA (320–400 nm) ranges (21 CFR § 352, 2024). The SPF value reflects how effectively a sunscreen protects against sunburn caused by UVB radiation. The process begins with sample preparation, where the sunscreen is applied uniformly to a substrate that mimics human skin, such as a roughened polymethyl methacrylate, PMMA, plate, or Transpore tape, at a standard dosage of 2 mg/cm². For this experiment, I used PMMA plates. After application, the sunscreen can dry for a specified time to simulate real-world use (Pelizzo, 2012).
The spectrometer is calibrated using a blank substrate to establish a baseline measurement. The sunscreen-coated substrate is then placed in the spectrometer, and transmittance readings are taken across the UV range (Pelizzo, 2012). These measurements are converted to absorbance values and analyzed using the erythema action spectrum, which accounts for the skin's sensitivity to UV radiation, and the solar UV spectrum, reflecting natural sunlight distribution. The SPF value is calculated using a formula that integrates these factors to compare the erythemal effect with and without sunscreen protection. F-1 shows the results of the critical wavelength test. This test demonstrates the ability of the product to cover UVA as well as UVB coverage, meaning it qualifies for the FDA guidelines for broadspectrum (21 CFR § 352, 2024).
F-1. In vitro analysis of critical wavelength absorbance
This approach estimates how much longer a person can be exposed to the sun with sunscreen before burning relative to unprotected skin. For example, SPF 15 blocks approximately 93% of UVB rays, SPF 30 blocks about 97%, and SPF 50 blocks around 98% (Pelizzo, 2012). While UV spectrometry offers a non-invasive, efficient method for evaluating sunscreen efficacy, in vitro, results may differ from in vivo outcomes due to real-world factors like skin interaction and environmental conditions. Also, the application thickness of the SPF of the PMMA plates can wildly change the SPF results (Pelizzo, 2012). So although the in vitro method gives cost effect results I needed to follow up with an actual in vivo test with a third party testing lab.
SPF Testing: Methodology and Consumer Evaluation
In vivo, determination of SPF value involves testing the sunscreen's effectiveness on human skin under controlled conditions to measure its ability to prevent erythema caused by UVB radiation. The process typically follows standardized protocols, such as those outlined by the U.S. Food and Drug Administration. Volunteers with a range of skin types are recruited, and a small area of their skin, often on the back or forearm, is exposed to artificial UV radiation from a solar simulator (21 CFR § 352, 2024). Before exposure, the sunscreen is applied evenly to designated test areas at a standard dose of 2 mg/cm² and allowed to dry. The minimum erythema dose or MED, which is the smallest amount of UV radiation that causes visible reddening of the skin after 24 hours, is measured for both protected and unprotected skin. The SPF value is then calculated as the ratio of the MED on sunscreen-protected skin to the MED on unprotected skin (21 CFR § 352, 2024). This method provides a direct, real-world measure of sunscreen efficacy, though it requires ethical considerations and careful participant monitoring to minimize risks associated with UV exposure.
When evaluating an SPF for aesthetics, the general consensus is to use consumer product testing groups to do double-blind trials against similar or competitive products. Given that my budget for this project could not accommodate this type of expense, I utilized a group of 5 subjects and conducted a single-blind trial compared to a popular brand called Think Sport (control). I allowed subjects to individually apply the SPF on one side of their face and the control on the other. I then asked the subjects to gauge various attributes of each SPF on a scale of 1-5, with 5 being the most undesirable attribute. The evaluation categories were white cast upon application, oily after-feel, sticky feel upon dry-down, ease of application, and gritty feel upon application. The average of each category was taken and graphed for comparison (F-2). The two most prominent features in comparison were the reduction of oily after-feel and ease of application. These features were most likely due to the usage of the ester dicaprylyl carbonate and C12-15 alkyl benzoate, which is known to have a silky after-feel (Abou-Dahech, 2020).
F-2. Aesthetic evaluations of SPF aesthetics versus industry leader
Improving Formulation Knowledge and Creating Safer Sunscreen Solutions
During this process I found most ingredients based information was available in industry publications, however formula based knowhow such as predicting the interacting of various ingredients were hard to find. In the future it may be an interesting tool to give new formulators the tools to predict various interactions with ingredients or formulas such as the medical community has with drug interactions. Overall, the creation of this sunscreen has shown that with an intensive search in literature, it is possible to create unusual cosmetic formulas that have not been experienced before. On a personal note myself and others feel safer going on runs knowing that the sunscreen I am wearing not only feels great, but protects my skin.
References:
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Title 21, Code of Federal Regulations (CFR) § 352 (2023)
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Jocelyn Manfut (left) and Nikita Gill (right)Sun Deep Cosmetics
Jocelyn Manfut (left) and Nikita Gill (right)Sun Deep Cosmetics
For athletes, sweat and water exposure are routine, yet sunscreen efficacy decreases when exposed to moisture.AdobeStock By Antonioguillem
F-1. In vitro analysis of critical wavelength absorbance
F-2. Aesthetic evaluations of SPF aesthetics versus industry leader
