Determination of SPF in vitro

Determining the SPF in vitro allows for the evaluation of a sunscreen product's ability to protect the skin against UVB radiation, without the need for testing on volunteers. This analysis is essential for manufacturers of sunscreens, protective lotions, day creams with SPF, or cosmetic formulations claiming photoprotective action. It ensures a reliable, standardized, and reproducible measurement of the Sun Protection Factor, in accordance with regulatory requirements and best practices in the cosmetics industry.

Industrial implications of determining the SPF

The SPF (Sun Protection Factor) is a key performance indicator for sunscreens. An inaccurate or non-compliant calculation can lead to misleading claims, consumer safety, or regulatory non-compliance. In vitro analysis allows for:
• validating the advertised UVB protection
• optimizing photoprotective formulations
• comparing efficacy between prototypes
• verifying product stability after thermal stress, light exposure, or aging
• documenting regulatory dossiers before market launch

This method is particularly useful for accelerating the development of new products by limiting the use of in vivo testing.

Analytical method: spectrophotometry according to ISO 24444/COLIPA

The SPF is evaluated by spectrophotometry after controlled application of the product onto quartz or PMMA plates. These substrates reproduce the optical properties of skin and allow for a standardized measurement of UV transmission.

The procedure involves:
• applying the product according to a defined dosage
• measuring UVB transmission through the applied film
• calculating the SPF according to ISO 24444 or COLIPA methodologies

This approach guarantees:
• high reproducibility
• interpretation in accordance with international standards
• a faster and more ethical method than in vivo testing

Additional analyses such as the determination of UVA-PF or the calculation of Critical Wavelength may be associated according to regulatory requirements.

Matrices analyzed and applications

This analysis applies to all types of products claiming photoprotection: sunscreens, sun lotions, sprays, protective oils, SPF day creams, protective foundations, prototype formulations, UV active ingredients or innovative materials dedicated to sun protection.

It addresses the following needs:
• rapid evaluation of prototypes in R&D
• validation of SPF claims before market launch
• optimization or comparison of UV filters (organic, mineral)
• quality control of production batches

YesWeLab Support

YesWeLab collaborates with a network of expert laboratories in cosmetic and photoprotection analysis, most of which are certified or accredited according to ISO 17025 and COFRAC standards. We support cosmetic brands, formulators, and R&D laboratories in selecting the most suitable tests (in vitro SPF, UVA-PF, UV stability, photodegradation) and in interpreting the results.

Our digital platform simplifies request management, sample tracking, and rapid access to results. Since 2020, numerous cosmetic companies have relied on YesWeLab to secure their SPF claims and accelerate their time to market.

Other analyses from the YesWeLab catalogue

• Photostability studies
• Analysis of UV filters by HPLC/LC-MS