ABSTRACT
The history of an inflamed acne lesion normally starts with a comedone colonized by entrapped bacteria of the genus Propionibacterium. Comedones occur as a result of hyperkeratinization of the cells lining the orifice of sebaceous follicles, and they form when an increased rate of sebum production accompanies a simultaneous blockage of the sebaceous gland openings. A comedone can be manifested as a microcomedone, which is not visible to the naked eye, a black-or whitehead, or a macrocomedone. There is a significant correlation between the severity of acne and the number and size of microcomedones. It is therefore pivotal for the manufacturers of topical agents to know if their products increase the number and size of comedones, and thus have a comedogenic effect. Conversely, in case of all products designed for the treatment or prevention of acne, their potency with regard to the reduction of microcomedones, thus their comedolytic activity, has to be known. In principle, three assays are available to assess the comedogenic or comedolytic activity of compounds and final formulations of topical products.
