Overview
EN ISO 18861:2021 (ISO 18861:2020) - Cosmetics - Sun protection test methods - Percentage of water resistance - defines a standardized, reproducible procedure to evaluate how much sun protection a sunscreen retains after water exposure. The standard compares the static SPF (before immersion) with the wet SPF (after a defined water immersion procedure) and expresses water resistance as a percentage retention. It is intended for manufacturers, test laboratories and regulatory bodies to substantiate water‑resistance claims for sun care products.
Key topics and requirements
- Purpose: Determine the percentage of SPF retention after water immersion by comparing pre‑ and post‑immersion SPF values.
- Referenced methods: Uses the in‑vivo SPF measurement procedure of ISO 24444 and the water immersion protocol of ISO 16217.
- Test subjects: Human panel testing in accordance with ISO 24444; at least 10 subjects shall be selected.
- Test set‑up: Product sites are located between the scapula line and the waist and configured for full immersion in a simulated swim test device (design information in Annex A).
- Water immersion sequence: A defined immersion/rest chronology is specified (see ISO 16217 and Annex B) - the standard includes example immersion and drying steps (e.g., 20 min immersion with circulating water plus drying interval).
- Calculations: Individual and mean percentage of water resistance are calculated (sections 5.4–5.5), including computation of lower confidence limits (section 5.6) to support statistical assessment.
- Reference product and acceptance criteria: Standard reference sunscreen and acceptance criteria for control product P2 are provided (section 4.6 and 5.7, Annex C).
- Reporting: Required test report elements and data handling are specified (section 6).
Practical applications
- Substantiating product claims such as “water‑resistant” or “very water‑resistant” for marketing and regulatory compliance.
- Quality control and formulation optimization during product development to measure how surfacing, film formers, or UV filters affect SPF retention in water.
- Comparative testing of product variants, batch verification, and third‑party certification testing by accredited laboratories.
- Regulatory dossiers where objective, reproducible evidence of water resistance is required.
Who uses this standard
- Sunscreen and cosmetics manufacturers
- Independent testing laboratories and contract research organizations (CROs)
- Regulatory agencies and conformity assessment bodies
- R&D and product validation teams assessing sun protection performance in aquatic conditions
Related standards
- ISO 24444 - In vivo determination of SPF (required SPF test method)
- ISO 16217 - Water immersion procedure for determining water resistance (required immersion protocol)
For definitive procedures, timelines and full calculation methods, consult the full text of EN ISO 18861:2021 / ISO 18861:2020 and the normative references (ISO 24444, ISO 16217).
