5 Facts About Physical Sunscreen: How It Works, Its Benefits, and the Importance of Strategies SPF Testing
Exposure to ultraviolet (UV) radiation is one of the environmental factors that can affect skin health. For this reason, sunscreen plays an important role in protecting the skin from UV exposure.
Among the various types of sunscreen available, physical sunscreen, also commonly known as mineral sunscreen, is widely used in skincare products. Physical sunscreens generally use zinc oxide (ZnO) and titanium dioxide (TiO₂) as inorganic UV filters.
However, does physical sunscreen simply reflect UV radiation? And is the presence of these active ingredients enough to guarantee that a product provides the SPF protection stated on its label?
Here are five important facts about physical sunscreen, from how it works to why SPF testing matters.
Table of Content:
- 1. Physical Sunscreen Uses Mineral UV Filters
- 2. Physical Sunscreen Does More Than Simply “Reflect” UV Rays
- 3. Physical Sunscreen Can Provide Protection Against UVA and UVB
- 4. Zinc Oxide or Titanium Dioxide Does Not Automatically Determine the SPF Value
- 5. SPF Testing Is Important for Supporting Sunscreen Claims
- From Formulation to Claims: Why Testing Matters
1. Physical Sunscreen Uses Mineral UV Filters
Physical sunscreens generally rely on zinc oxide and titanium dioxide as active ingredients to help protect the skin from ultraviolet radiation. Zinc oxide provides broad protection across the UVA and UVB spectrum, while titanium dioxide provides strong protection, particularly within the UVB range.
Because these ingredients are inorganic materials, they are commonly referred to as mineral or inorganic UV filters. The performance of these mineral filters, however, does not depend solely on their presence in a formulation.
Their concentration, particle characteristics, dispersion, and interaction with other ingredients can influence the overall performance of the final sunscreen product.
Read Also:
Sunscreen Labeled SPF 50: Does the Value Match the Test Results?
2. Physical Sunscreen Does More Than Simply “Reflect” UV Rays
A common misconception is that physical sunscreen works exclusively by creating a protective layer on the skin that reflects UV radiation. In reality, its mechanism is more complex.
Mineral UV filters such as zinc oxide and titanium dioxide can interact with ultraviolet radiation through a combination of absorption, scattering, and reflection. Therefore, the term “physical sunscreen” should not be interpreted as meaning that all incoming UV radiation is simply reflected away from the skin.
Particle size, material characteristics, dispersion, and the overall formulation can also influence the optical properties and UV protection performance of a sunscreen.
3. Physical Sunscreen Can Provide Protection Against UVA and UVB
Ultraviolet radiation that reaches the skin primarily includes UVA and UVB. These wavelengths have different characteristics and biological effects, making broad-spectrum protection an important consideration when developing sunscreen products.
Sun Protection Factor (SPF) primarily indicates protection against UV-induced erythema or sunburn, to which UVB makes a major contribution. UVA protection, meanwhile, needs to be assessed using appropriate parameters and testing methods.
Zinc oxide is known for its relatively broad UVA and UVB coverage, while titanium dioxide has a different UV absorption profile. For this reason, the selection and combination of UV filters, together with the overall formulation, can significantly influence the final protection provided by a sunscreen.
4. Zinc Oxide or Titanium Dioxide Does Not Automatically Determine the SPF Value
The ingredient list alone cannot confirm whether a sunscreen provides a specific SPF value. Sunscreen performance can be influenced by several factors, including the type and concentration of UV filters, particle size and distribution, formulation vehicle, film-forming properties, product application, and interactions between ingredients.
Therefore, simply including zinc oxide or titanium dioxide in a formula does not automatically mean that the product will achieve SPF 30, SPF 50, or any other specific SPF value. This is why sunscreen claims should be supported by testing of the final formulation, rather than relying solely on assumptions based on the active ingredients.
5. SPF Testing Is Important for Supporting Sunscreen Claims
So, how can manufacturers determine whether a physical sunscreen actually provides the targeted SPF protection? This is where SPF testing becomes essential. One internationally recognized standard is ISO 24444:2019, which specifies an in vivo method for determining the Sun Protection Factor of sunscreen products.
The method provides a standardized approach for evaluating a product's ability to protect human skin against erythema induced by solar-simulated ultraviolet radiation. In addition to in vivo testing, in vitro approaches have continued to develop.
ISO 23675:2024, for example, provides an in vitro method for determining SPF. Research has also evaluated its application to sunscreen formulations containing high concentrations of zinc oxide and products formulated exclusively with inorganic UV filters.
Therefore, SPF testing provides objective data on sunscreen performance and helps support product protection claims using relevant standardized methods.
From Formulation to Claims: Why Testing Matters
Physical sunscreen provides UV protection through mineral filters such as zinc oxide and titanium dioxide. However, sunscreen performance cannot be determined solely by looking at which active ingredients are included in the formula.
The concentration and characteristics of the UV filters, particle properties, formulation system, and ability of the product to form a uniform film can all influence its final performance. For sunscreen manufacturers, skincare brands, and R&D teams, testing serves as an important bridge between product formulation and the protection claims communicated to consumers.
Need to Evaluate the SPF of Your Sunscreen Product?
For companies developing sunscreen, skincare, or cosmetic products, SPF testing can provide measurable data to evaluate product performance and support relevant protection claims. IML Testing & Research provides SPF testing services to help companies evaluate the UV protection performance of sunscreen products through appropriate testing methods.
Free consult with the IML Testing & Research team to discuss the testing method that best suits your product and development needs.
Author & Editor: Lina
References
Schneider, S. L., & Lim, H. W. (2019). A review of inorganic UV filters zinc oxide and titanium dioxide. Photodermatology, Photoimmunology & Photomedicine, 35(6), 442–446. https://doi.org/10.1111/phpp.12439
Smijs, T. G., & Pavel, S. (2011). Titanium dioxide and zinc oxide nanoparticles in sunscreens: Focus on their safety and effectiveness. Nanotechnology, Science and Applications, 4, 95–112. https://doi.org/10.2147/NSA.S19419
Cavalcanti, I. M. G. A., Valeriano, C. C. S., Marçal, A. C., Novais, A. L. F., & Souza, D. N. (2025). Optical and structural properties of sunscreens evaluated by physical techniques with emphasis on zinc oxide: A critical review. Applied Radiation and Isotopes, 226, 112217. https://doi.org/10.1016/j.apradiso.2025.112217
Pissavini, M., Pouradier, F., Lapalud, P., Batzer, J., Contier, M., & Matts, P. (2025). The double plate in vitro SPF test method (ISO 23675:2024) is a reliable means of measuring the performance of sunscreen products with high concentrations of zinc oxide and inorganic-only UV filters. Photochemical & Photobiological Sciences, 24(10), 1797–1805. https://doi.org/10.1007/s43630-025-00798-5
International Organization for Standardization. (2019). ISO 24444:2019 Cosmetics — Sun protection test methods — In vivo determination of the sun protection factor (SPF). Geneva: ISO.
