Study of the photostability of a sunscreen product

The study of the photostability of a sunscreen product aims to evaluate the resistance of UV filters and the complete formula when exposed to light, whether natural or artificial (UV-A, UV-B or full spectrum).
This analysis makes it possible to verify that the product retains its photoprotective efficacy (SPF) , its chemical stability and its safety of use throughout its exposure.

Photostability is an essential regulatory and scientific criterion in the development of sunscreen products (creams, sprays, oils, gels), but also for cosmetic formulations containing photosensitive active ingredients such as retinoids, vitamins or certain plant extracts.

The main objective of the study is to:

• Measure the degradation of UV filters after irradiation.
• Evaluate interactions between filters , which may lead to a loss of efficiency.
• Identify photodegradation by-products , which are sometimes potentially irritating or unstable.
• Ensure regulatory compliance and marketing performance of the final product.

Analytical methods used

The study of photostability combines physical, chemical and analytical tests according to international standards (ISO 24443, COLIPA, FDA).

Common steps include:

• Controlled irradiation under UV-A/UV-B lamp or solar simulator (full spectrum).
• Analytical monitoring of UV filters by HPLC-DAD , LC-MS/MS or UV-Visible spectrophotometry , in order to detect concentration losses or the formation of derivatives.
• Visual and organoleptic analysis of the product before and after exposure (color, odor, texture).
• In vitro measurement of SPF or UVA index to assess the persistence of photoprotection.

These methods ensure a complete evaluation of the photochemical behavior of the product under controlled and reproducible conditions.

Affected matrices

The photostability study applies to a wide range of cosmetic products:

• Sun creams and milks , with organic and mineral filters.
• Photoprotective sprays, oils and gels , intended for direct exposure.
• Facial care products or makeup containing UV filters .
• Formulations based on sensitive active ingredients (vitamin C, retinol, plant extracts, natural colorants).

This study can be performed on final formulations , prototypes in development or regulatory stability batches .

Industrial and regulatory applications

The study of photostability constitutes a crucial step in the development and validation of solar products . It allows:

• To validate the robustness of the formula before marketing.
• To support the SPF claim and the product's stability in the sun.
• To meet European and international regulatory requirements , in particular for the safety of UV filters listed in Annex VI of Regulation (EC) No. 1223/2009.
• To prevent premature degradation of the product under real-life conditions of use.
• The results obtained are also used in technical files (PIF) and cosmetic safety assessments (CPSR) .

Related analyses

For a complete assessment of the stability and performance of the solar product, it is recommended to combine:

• The stability test to study the physicochemical evolution of the product.
• The accelerated stability test to simulate aging at high temperature and humidity.
• Oxidation stability of fats and oils , particularly relevant for lipophilic formulations.

YesWeLab expertise

YesWeLab relies on a network of ISO 17025 and COFRAC accredited partner laboratories , specializing in stability and photoprotection analyses of cosmetic products.

Thanks to the YesWeLab digital platform , you can order your analyses, track your samples and consult your reports online , for rapid and centralized monitoring.

For any specific request, contact our scientific team to design a study protocol adapted to your sunscreen formulation.