Is mineral oil comedogenic?

The phrase, “acne cosmetica” was coined in the early 1970s to describe the association between cosmetic use and acne breakouts in women over the age of 30. Cosmetic formulations at that time did contain a number of animal, mineral, and vegetable oils, as well as synthetic oils (esters) which were thought to clog pores and perhaps elicit the response. A number of methods were quickly developed to evaluate the comedogenic potential of these ingredients, and several of these were found to evoke a response in the rabbit’s ear. This quickly became the model of choice. Several years later, a human model was developed, and researchers noted a difference between the results. Several ingredients elicited less of a comedogenic response. At this point in time, a great deal of confusion in interpreting comedogenic results existed. Both dermatologists and those in the cosmetic industry were unsure of the significance, if any, that the reported data held with respect to “acne cosmetica. ” In an attempt to understand the contrasting results between the animal and human models, the American Academy of Dermatology (AAD) held an international symposium on comedogenicity. 1 Several factors were taken into account (methodology, experimental design, results obtained, etc.), and based on the data presented, the symposium concluded that “if the animal model does not show evidence of comedogenesis, the test material under consideration is unlikely to be comedogenic in human skin. One-plus reactions are also unlikely to cause reactions in humans. Two-plus or three-plus responses require sound scientific judgment. Reformulation should be considered or the product should be adequately tested in humans before general use. ” It should be noted that the comedogenic grades used in this statement are based on a 0 (no activity) to 3 (severe activity) scale, and that researchers were reporting results using a 0 (no activity) to 5 (severe activity) scale. Therefore, when interpreting the reported data, the AAD-recommended values would have to be shifted to include a one-plus to a two-plus for “unlikely to be comedogenic” and grades three-plus to five-plus “would require reformulation or adequate testing in humans. ” So, “is mineral oil comedogenic? ” This is a question that physicians, estheticians, cosmetic marketers, and consumers have asked me several times a year for the last two decades. Looking over the animal data that have been generated over the years (published 2–5 and unpublished) using the rabbit ear model, mineral oil elicits a comedogenic grade ranging from 0 to 2 on a 5-point scale (Table 1). Taking into account the AAD recommendations, mineral oil would be categorized as “unlikely to be comedogenic in human skin. ” To determine if this conclusion could be considered accurate, a number of finished products containing mineral oil were evaluated using the human model. These products ranged in mineral oil concentration from approximately 0.5% to 30%. The testing was conducted as outlined by Mills and Kligman. 6 However, in order to avoid a subjective grading, the mean ratio of follicles to microcomedones was obtained for both pre-application and postapplication sites, and a percent change from baseline was calculated to determine the degree of microcomedone formation. This allows the data to be expressed in the form of a percent, yielding a clearer picture of the comedogenic activity. The data depicted in Table 2 presents the percent change in microcomedone activities for the products tested (9– 34%). The percent change from baseline is within the normal range of ± 10% of the negative control (15–30%) tested and can therefore be considered noncomedogenic in humans. Additionally, based on the 85–95% change in Correspondence: Joseph C DiNardo, PCR, 7413 Whitepine Road, Richmond, VA 2337. E-mail: jmjdinardo@aol.com