With increasing consumer awareness of skin health protection, UV protection has become a core indicator in cosmetics R&D and evaluation. UVA (ultraviolet A) rays, due to their strong penetrating power and ability to penetrate deep into the dermis, can cause long-term exposure to them, leading to photoaging, hyperpigmentation, and even an increased risk of skin cancer. Therefore, scientific evaluation of cosmetics' UVA protection is particularly important. Traditional sunscreen effectiveness evaluation relies on in vitro SPF (sun protection factor) testing, but SPF primarily reflects a product's protection against UVB, while UVA protection is often overlooked. To this end, instrumental testing methods for cosmetics' UVA protection have been gradually promoted and established internationally to accurately quantify UVA protection performance. This method simulates the UVA component of the solar spectrum and utilizes precision testing equipment such as spectrometers, integrating sphere systems, and UV light sources to measure the attenuation of UVA radiation by cosmetics on skin simulants or reflective panels. The resulting UVA protection index (PA value) or UVA protection factor (PFA) is then calculated. In recent years, my country has gradually introduced and improved relevant testing standards, such as GB/T 34867-2017, "Determination of UVA Protection of Cosmetics," providing cosmetics companies with scientific and practical technical support. This article systematically introduces the test items, key testing instruments, standard testing methods, and current testing standards for the instrumental determination of UVA protection of cosmetics, helping companies and research institutions fully understand this technical framework.
The UV Protection Factor (UVPF) accurately assesses the effectiveness of sunscreens at different UV intensities, ensuring that the products we choose provide adequate sun protection. Professional testing not only reveals the SPF of a sunscreen but also confirms its ability to effectively absorb or reflect UV rays to prevent skin damage. SPF testing objectively and accurately assesses sun protection effectiveness, providing consumers with a reliable basis for selection. Through testing, we can understand the protection provided by sunscreens at different UV intensities and choose the one that best suits our needs.
Core Indicators for Cosmetics' UVA Protection
Testing for cosmetics' UVA protection primarily focuses on the "UVA Protection Factor" (PFA) and "PA Grade" assessments. The PFA value indicates a product's ability to protect against UVA radiation under specific conditions. It is calculated based on the reduction in UVA transmittance through a skin simulant after application of the sample. The PA grade (e.g., PA+, PA+++, PA++++) is a grading of the PFA value that provides a visual representation of a product's UVA protection. Furthermore, testing may also include an assessment of the "UVA/UVB ratio" to determine whether a product provides balanced broad-spectrum protection. These indicators collectively constitute the core system for evaluating cosmetics' UVA protection and serve as a crucial basis for product labeling and market regulation.
Technical Support for High-Precision UVA Protection Assessment
Instrumental measurement of cosmetics' UVA protection requires a range of high-precision, standardized testing equipment. Core instruments include:
UV light source system: Typically uses a xenon lamp or LED light source. Its spectral output must cover the UVA band (320–400 nm) and meet the sunlight simulation spectrum requirements specified in ISO 24444.
Spectrometer: Used to accurately measure the radiant intensity after exposure. Its wavelength resolution must be less than 1 nm and its signal-to-noise ratio must be high to ensure data accuracy.
Integrating sphere system: Used to collect reflected or transmitted UV light, ensuring that the measurement is unaffected by angle. It is commonly used to measure the UVA transmittance of skin simulants or sample substrates.
Sample coating device: Such as a standard applicator or automatic applicator, ensures that the sample is evenly and quantitatively applied to the test substrate (such as a polytetrafluoroethylene sheet or skin simulant membrane). The standard thickness is typically 1.5 mg/cm².
Data acquisition and analysis software: Integrates spectral data processing, PFA value calculation, PA grade determination, and other functions, and integrates with testing standards to achieve automated evaluation.
UV transmittance testers typically use spectral analysis principles to calculate a sample's UV transmittance by measuring the ratio of the intensity of transmitted light to the intensity of incident light within the UV band. The instrument typically includes a light source, spectrometer, and detector, allowing precise control of the UV wavelength emitted by the light source and measuring the sample's absorption, reflection, and transmission of UV light.
Testing Method and Procedures
Human Test Method
The delayed skin darkening (PPD) method is currently the most widely used human evaluation method for evaluating the UVA protection performance of sunscreen cosmetics. my country's "Cosmetics Safety Technical Specifications" (2015 Edition) references this method and proposes the "Determination of the Long-wave UV Protection Index (PFA) of Sunscreen Cosmetics."
The principle is to use a xenon arc lamp as a light source, emitting 320-400nm UV light to irradiate human skin. Two to four hours after irradiation, the minimum UV dose or shortest exposure time required to produce a slight darkening of the entire exposed area is observed, which is known as the minimum persistent darkening dose (MPPD). The UVA protection effectiveness of a sunscreen product is determined by calculating the ratio of the MPPD required to produce darkening of skin protected by the sunscreen to the MPPD required to produce darkening of unprotected skin.
The UVA protection rating (PA) is indicated on the product label based on the measured PFA value. A PFA value less than 2 does not indicate UVA protection, indicating that the product's protection against long-wave UV rays is minimal. A PFA value of 2-3 is labeled PA+; a PFA value of 4-7 is labeled PA++; a PFA value of 8-15 is labeled PA+++; and a PFA value of 16 or greater is labeled PA++++. A higher PA rating indicates a better sun protection effect. For example, a sunscreen lotion with a measured PFA value of 6 should be labeled PA++ on its label to provide consumers with an intuitive understanding of its UVA protection capabilities.
In vitro testing method
Based on the spectrophotometric testing principle: In vitro testing involves evenly applying the sunscreen cosmetic onto an artificial carrier and measuring its transmittance or absorbance in the UVA band using a spectrophotometer or other similar instrument to assess the product's UVA protection. While the principles of in vitro testing methods are generally consistent across countries, there are significant differences in the specific operational details.
This instrument uses menu-driven software that guides users step-by-step through the industry-standard testing process. The built-in reporting function automatically generates key data analysis and reports in a standardized industry-compliant format. The report contains essential information such as date, time, operator, sample number, and test parameters. Users can conveniently access the report on a PC, print it directly, or export it to data processing software for in-depth analysis and review.
In summary, instrumental testing of cosmetic UVA protection plays a key role in evaluating product protection. From the definition of core indicators, to the support of high-precision testing instruments, to the implementation of specific testing methods such as human testing and in vitro assays, a scientific, rigorous, and continuously improved evaluation system has been established. This not only helps cosmetics companies accurately control product quality and provide consumers with more reliable and effective sunscreen products, but also provides a strong basis for market regulation, driving the entire cosmetics industry towards a more focused and scientifically standardized approach to skin health protection, better meeting consumers' growing demand for skin health.
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