Study of the photostability of a sunscreen product

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

Photostability is an essential regulatory and scientific criterion in the development of sun 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:

• Measuring the degradation of UV filters after irradiation.
• Evaluate the interactions between filters , which may lead to a loss of efficiency.
• Identify the by-products of photodegradation , 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).

Typical 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, smell, texture).
• Measurement of SPF in vitro or UVA index to assess the persistence of photoprotection.

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

Matrices involved

Photostability testing applies to a wide range of cosmetic products:

• Sunscreen creams and lotions , 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 carried out on final formulations , prototypes in development or regulatory stability batches .

Industrial and regulatory applications

The study of photostability is a crucial step in the development and validation of sunscreens . It allows us to:

• To validate the robustness of the formula before commercialization.
• To support the SPF claim and the product's stability in sunlight.
• 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-world conditions of use.
• The results obtained are also used in technical dossiers (PIF) and cosmetic safety assessments (CPSR) .

Related analyses

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

• The stability test to study the physico-chemical 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's expertise

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

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

For any specific request, contact our scientific team so that we can design a study protocol adapted to your solar formulation.