At Siperstein Dermatology Group, we emphasize the importance of daily sun protection to prevent skin cancer and premature aging. But how does sunscreen actually work? Understanding its mechanisms can help you make informed choices about the best protection for your skin.
The Science Behind Sunscreen
Sunscreens shield your skin from ultraviolet (UV) radiation, which consists of:
- UVA (320–400 nm): Penetrates deep into the skin, leading to aging and long-term DNA damage.
- UVB (290–320 nm): Causes sunburn and plays a major role in skin cancer development.
Sunscreens use two main types of active ingredients to block or absorb these harmful rays:
Chemical Sunscreens: UV Absorption
Chemical sunscreens contain organic (carbon-based) compounds that absorb UV radiation and convert it into harmless heat. These compounds are designed to cover different parts of the UV spectrum:
- UVB Filters: Octinoxate, cinoxate
- UVA Filters: Oxybenzone, sulisobenzone
- Broad-Spectrum Filters: Ecamsule, bisoctrizole
Because different chemicals absorb different wavelengths, most sunscreens combine multiple ingredients for broad-spectrum protection.
Physical (Mineral) Sunscreens: Reflection and Absorption
Physical sunscreens, like zinc oxide (ZnO) and titanium dioxide (TiO₂), work by reflecting and scattering UV rays. However, recent research shows that these minerals also absorb UV radiation, making them more effective than previously thought.
- Zinc Oxide: Covers UVA and UVB protection.
- Titanium Dioxide: Primarily blocks UVB.
To improve cosmetic appeal, many physical sunscreens now use micronized or nanoparticle formulations, reducing the white cast while maintaining effectiveness.
Measuring Sunscreen Effectiveness
Sunscreen efficacy is determined by three key factors:
- Sun Protection Factor (SPF): Measures UVB protection by comparing the time it takes for skin to burn with and without sunscreen.
- PPD Testing: Persistent Pigment Darkening (PPD) measures UVA protection by evaluating how much pigmentation develops in sunscreen-protected skin compared to unprotected skin. While this test is commonly used in Europe and Japan, it is not a standard method in the U.S. Instead, the FDA uses the critical wavelength test, which labels sunscreens as “broad spectrum” if they absorb 90% of UV radiation at wavelengths of 370 nm or higher.
- Substantivity: This refers to a sunscreen’s ability to remain effective despite exposure to water, sweat, or rubbing. The FDA defines “water resistance” as the ability to retain UV protection after two 20-minute water immersion periods. High substantivity is especially important for outdoor activities and sports.
Safety and Environmental Considerations
Concerns have been raised about the systemic absorption of some chemical filters, particularly oxybenzone. While studies have detected sunscreen ingredients in blood and urine, no conclusive evidence links them to harmful health effects. Nevertheless, regulatory bodies continue to evaluate their safety.
Additionally, some sunscreen ingredients, such as oxybenzone and octinoxate, have been associated with coral reef damage, leading to bans in places like Hawaii and Key West. Mineral-based sunscreens are often considered a safer choice for the environment.
Choosing the Right Sunscreen
For optimal protection, we recommend:
- Broad-spectrum sunscreen with SPF 30 or higher.
- Water-resistant formulas if sweating or swimming.
- Mineral sunscreens for sensitive skin or eco-friendly protection.
- Daily application, even on cloudy days.
Sunscreen is one of the best tools to protect your skin from premature aging and skin cancer. If you have questions about the best sunscreen for your skin type, visit Siperstein Dermatology Group—we’re here to help you stay protected and informed!
Reference: Chałupczak NV, Lio PA. Sunscreens: Mechanisms and Safety in Depth. J Drugs Dermatol. 2025;24(2):142-146. doi:10.36849/JDD.8102
