The water resistance study consists of the measurement of the sun protection factor (SPF) after water immersions of the studied product with the participation of volunteers (so-called in vivo methodology). The product is applied on the skin of the volunteer in the amount of 2 mg/cm2 and is subjected to water immersion at different time durations. After the water immersion, skin is irradiated with UV light in controlled doses to induce erythema. Based on erythema readouts for the control and test areas, the SPF after the immersion is calculated and used for water resistance claims.
Regulations regarding water resistance testing of sunscreens vary between regions and countries. In this article, you can find a general overview of exemplary regions.
European Union:
In the EU, sunscreens are regulated under the Cosmetic Products Regulation. Water resistance testing is required for sunscreen products claiming to provide water resistance. The standard used for testing is typically the International Organization for Standardization (ISO) standard. The water resistance claim is supported by a comparison of SPF measured before and after the bath of a minimum of 10 volunteers.
The claim is described in Cosmetic Europe Document N°16: WATER RESISTANCE LABELLING (2005), where there is a distinction between water resistance (WR) and very water resistance (VWR) claims differing in the time of water immersion (respectively 40 and 80 minutes). The product is claimed WR or VWR when the water resistance percentage is a minimum 50%, which means that the product after immersion has to have the SPF value of a minimum of 50% SPF before immersion value.
For the proper measurement and calculation of WR percentage, testing laboratories use three ISO standards: ISO 24444 Cosmetics – Sun protection test methods – In vivo determination of the sun protection factor (SPF), ISO 16217 Cosmetics – Sun protection test methods – Water immersion procedure for determining water resistance and ISO 18861 Cosmetics – Sun protection test methods – Percentage of water resistance.
Australia:
Sunscreens in Australia are regulated by the Therapeutic Goods Administration (TGA). Products claiming water resistance must undergo testing according to the Australian/New Zealand standard AS/NZS 2604:2021 Sunscreen products – Evaluation and classification. The standard also specifies the requirements for water resistance testing and labelling. The document is in high accordance with ISO standards and references to ISO 24444 and ISO 16217. However, there are some differences regarding water immersion time durations.
Products of SPF less than 8 after water immersion cannot be recognized as water resistant. For SPF 8-less than 15 water immersion is 40 minutes, which is in accordance with ISO standards. However for SPFs 15-less than 30 water immersion increases to 2 hours, and for these of SPF 30 and above – 4 hours, which is out of the scope of ISO 16217. It can be concluded that water resistant testing and labeling guidelines are more restrictive than in the EU.
Sunscreens in Australia are also categorized into primary and secondary products. Water resistance primary sunscreen products may be labelled as “water resistant” when tested according to the standard. For secondary products, the label “water resistant” is optional.
United States:
In the United States, the Food and Drug Administration (FDA) regulates sunscreen products as Over-the-Counter (OTC) drugs. Sunscreens claiming to be water resistant must undergo in vivo testing according to Federal Register / Department of Health and Human Services / Food and Drug Administration – Labeling and Effectiveness Testing: Sunscreen Drug Products for Over-The-Counter Human Use (Vol. 76, No. 117 / Friday, June 17, 2011). The document describes the procedure of study conduct, SPF measurement, and labelling. FDA allows two levels of water resistance: 40 minutes and 80 minutes of water immersion. If a sunscreen meets the criteria for either of these levels, it can be labelled as water resistant (40 minutes) or water resistant (80 minutes). What is important, the SPF is measured only after water immersion, so there is no comparison before and after immersion. Thus, labelled SPF value refers to the value achieved after immersion, which differs from EU regulations.
To sum up, manufacturers need to adhere to the specific regulations in each country where they intend to sell their sunscreen products They need to ensure that they meet the required standards for water resistance testing and labelling.
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