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I am happy to have the opportunity to comment on the criticism by Dr Sayre and to correct some misunderstandings. It is correct that the subjects should apply sunscreens from jars containing a 15-g sample. There was a separate jar for each of the areas of the body studied, ie, a separate jar for the arm, a separate jar for the abdomen, a separate jar for the back, etc. The approximate area on which sunscreen was applied was about 30 × 20 cm. Consequently, a 15-g sample was not used to cover the entire body. If you apply 15-g of sunscreen on an area 30 × 20 cm, the layer thickness will be 25 mg/cm2. This means that there was no risk of "underdosage." The fact that each volunteer applied the product himself on his own back simply reflects the everyday situation.Concerning the matter of the
Larkö O. Sunscreen Application: Flawed Study?-Reply. Arch Dermatol. 1986;122(7):745–746. doi:10.1001/archderm.1986.01660190021003
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