Comedogenicity is the potential to promote follicular blockage leading to the formation of microcomedones and cosmetic acne. Mills and Kligman compared the established rabbit ear assay (REA) ratings with studies in human participants using the skin surface biopsy. They concluded that some materials considered comedogenic on REA were non-comedogenic in human skin.

Using a modification of the Mills and Kligman skin surface biopsy, this study aimed to determine the comedogenic potential of ten commonly used cosmetic oils: almond oil, argan oil, avocado oil, castor oil, coconut oil, grape seed oil, mineral oil, olive oil, safflower oil, and sunflower oil.

Each participant received a test patch with twelve chambers on the skin of the back, with each chamber containing filter paper saturated with each of the respective oils, the positive control (octyl palmitate), and the negative control (unsaturated filter paper). These patches were changed 3 times weekly for 4 weeks. Cyanoacrylate skin surface biopsies were done to determine the number of follicles and microcomedones at baseline and after 4 weeks of exposure.

Thirty individuals were enrolled in the study. All participants underwent baseline and final skin surface biopsies. Almond oil showed a significant increase with a 112.9% increase in the number of comedones from baseline.

The results of this study show that certain oils commonly used as ingredients in cosmetic products, such as almond oil, are comedogenic.