SESAMULS WO: Evaluating Sunscreen Product Water Resistance
In combination with the method for determining Sun Protection Factor (SPF), COLIPA has provided Guidelines for Evaluating Sun Product Water Resistance.
The protection provided by cosmetic products, whether the filters they contain are organic or inorganic, is neither permanent nor absolute. One of the main factors capable of invalidating the level of protection offered by these products is contact with water. For this reason, manufacturers of sun products have developed formulations that are able to retain their water resistance on the skin even after immersion in water. The principle on which water resistance testing is based is a comparison of a sunscreen product’s SPF, calculated after a very specific predetermined length of time immersed in water (wet SPF) with the value determined using the traditional method (static SPF), calculated in compliance with the International Sun Protection Factor method.
The test calls for a well-defined sequence of immersions in water. The procedure requires the use of a whirlpool bath. A sunscreen product is labelled “water resistant” (WR) if the effectiveness of its SPF following 2 immersions in water, each 20 minutes in length, is greater than 50% of its static, or initial, SPF. A product can be labelled “very water resistant” (VWR) if the verified effectiveness of the SPF after 4 immersions in water, each 20 minutes in length, is greater than 50% of its static SPF. The individual percentage of water resistance retention (%WRRi) is calculated as follows:
Where SPFiw = wet SPF, after water immersion and SPFis = static SPF