The ISO 18861 standard specifies the method of testing the water resistance of cosmetic sunscreen products, which aims to evaluate the protective effect of sunscreen products after water contact. The standard experimentally tests the sunscreen effect of sunscreen products under the influence of water immersion, sweat and other environments after use, and measures the percentage of sun protection effect attenuation. The core of the test method is to simulate the actual use situation to ensure the performance Stability of sunscreen products in water or wet environment. It is suitable for a variety of sunscreens, sprays and Miscellaneous sunscreen cosmetics to ensure that consumers can still get effective protection in underwater or high humidity environments. Through this test, manufacturers can ensure that their products meet the water resistance requirements, providing longer-lasting and reliable sun protection.