Abstract: Disclosed is an in-vitro method to determine efficacy of a cosmetic composition or of one or more ingredients comprised therein to inhibit a particulate pollutant from contacting skin, said method comprising the steps of: (i) contacting a human skin equivalent with a cosmetic composition to form, upon drying, a layer thereof extending along mutually perpendicular X and Y and Z axis where along said Z axis said layer is 1 to 100 ?m, where said Z axis indicates thickness of said layer; (ii) depositing, on said layer, a known amount of a model fine particulate matter comprising a first substance responsive to depth profile analysis where said cosmetic composition comprises a second substance, not comprised in said model fine particulate matter but also responsive to said depth profile analysis where the response of said first and second substances are distinguishable; (iii) for a pre-determined period after depositing said model fine particulate matter, periodically measuring response of said first and said seco