ISO 24443:2021

Overview

ISO 24443:2021 - "Cosmetics - Determination of sunscreen UVA photoprotection in vitro" defines a standardized in vitro method to characterize the UVA photoprotection of topical sunscreen products. The standard produces a UV spectral absorbance curve (290–400 nm) that can be used to compute parameters such as the in vitro UVA protection factor (UVA‑PF), critical wavelength, and UVA absorbance proportionality. The procedure relies on scaling the in vitro spectral data to a measured in vivo SPF (or an alternative ISO‑validated SPF method) and is not applicable to powder products (pressed or loose powders).

Key topics and technical requirements

• Spectral measurement range: 290 nm to 400 nm, wavelength step 1 nm (spectrophotometer requirements included).
• Substrate: acceptance of moulded and sandblasted PMMA plates with specified surface characteristics; product application adjusted (e.g., sandblasted plates at 1.2 mg/cm²).
• Calibration: mandatory calibration/validation of the spectrophotometer, UV exposure source, and radiometer; normative annexes provide calibration procedures.
• Photostability testing: samples are measured before and after a defined UVA irradiation dose (standard limits, e.g., up to 36 J/cm² in this edition) to assess photostability and post‑exposure UVA‑PF.
• Calculations: procedures for deriving UVA‑PF, critical wavelength (λc, 90% area), coefficient “C” for scaling in vitro to in vivo SPF (accepted range introduced: 0.6–1.6 under specific statistical conditions), and optional outputs for regulatory labeling.
• Reference materials: defined product reference sunscreens and a high UVA‑PF standard (P8) to validate laboratory performance.
• Reporting: required test report elements, number of determinations, and statistical guidance for valid results.

Practical applications

• Provides an in vitro alternative to in vivo UVA efficacy testing to:
  • Support product development and formulation optimization for broad‑spectrum UVA protection.
  • Perform quality control and batch verification of sunscreen UVA performance.
  • Generate evidence for regulatory labeling or claims where local rules accept in vitro UVA‑PF or critical wavelength data.
  • Screen photostability and to compare UVA protection before and after UV exposure.

Who uses this standard?

• Cosmetic formulators and R&D teams
• Third‑party testing and analytical laboratories
• Regulatory and compliance specialists in the cosmetics industry
• Quality assurance and product development groups seeking reproducible UVA performance data

Related standards

• ISO 24444 (in vivo determination of SPF) - used as the reference SPF for scaling in vitro spectral data.

Keywords: ISO 24443:2021, UVA‑PF, in vitro sunscreen testing, photoprotection, critical wavelength, PMMA plates, spectrophotometer, SPF, photostability, sunscreen lab testing.