In CR’s sunscreen tests, we use the Food and Drug Administration’s sunscreen testing protocol as a model. But as with all products, we do our own scientific, laboratory-based testing to identify differences in performance and give consumers a comparative evaluation.
We buy sunscreens at retailers, the way consumers do, and test three samples of each product, each from different manufacturing batches. For SPF, we test the sunscreens on three people, which is fewer than the FDA’s protocol calls for, but we use a statistical analysis to verify our results. A technician applies a standard amount of each product to a 2×3-inch rectangle on a panelist’s back before they soak in water for 40 or 80 minutes based on the product’s water resistance claims. Then we expose smaller sections of the rectangle to five or six intensities of simulated sunlight based on how quickly the panelist’s skin burns without protection. We also use a reference sunscreen with known performance to ensure testing accuracy. A day later, a technician examines the skin for redness and determines the sunscreen’s SPF.
To test for UVA, we apply sunscreen to plastic plates, expose them to UV light, and measure the amount of UVA and UVB rays that are absorbed. This test, like the UVA test in Europe, uses a process similar to the UVA test the FDA requires. But the test we use allows us to determine the degree of UVA protection, while the FDA test does not. The FDA test is pass-fail; a sunscreen that just passes gets the same designation—broad-spectrum—as one that screens out even more UVA.
Our ratings are developed from the average results of all the SPF and UVA tests for a sunscreen, as well as how much the average CR-tested SPF varies from the SPF listed on the label.
