To the Editor.—
While the basic premise expressed by Stenberg and Larkö, in "Sunscreen Application and Its Importance for the Sun Protection Factor" in the November 1985 issue of the Archives1 is plausible, there are serious problems with the study, the test data, and the interpretation, so much so that the report may mislead US physicians and consumers.Most important, the basic determination of application density is seriously flawed as follows: each volunteer was given only a 15-g sample of the product under test. A 15-g sample is just sufficient to cover an adult body at 1 mg/cm2. This irreparably biases the entire study and invalidates its conclusion. Further, each volunteer applied product to his own back. This also assured that less product was used, reducing the overall average application amount.The authors perform a sun protective factor test similar to the US Food and Drug Administration-proposed sunscreen