Microemulsions for Sprayable Delivery and Other Topics: Literature Findings

By: Charles Fox, Independent Consultant

Posted: March 30, 2010, from the April 2010 issue of Cosmetics & Toiletries.

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While permeation characteristics were correlative between human epidermis and PDMS membrane, the permeability in the PDMS membrane was significantly larger than in human epidermis. The findings were found to be different with the concurrent use of DEET insect repellent and sunscreen oxybenzone, where a synergistic permeation enhancement was observed. Further comparative studies are therefore necessary to understand these permeation mechanisms and the interactions between picaridin and oxybenzone.

Improving DHA efficacy: Burkhart et al. published a review on the use of dihydroxyacetone (DHA) and methods to improve its performance as an artificial tanning agent.⁴ DHA binds to proteins in the stratum corneum to impart a non-toxic, bronze color. The resulting pigments are called melanoidins, or brown chromophores.

The color is not removed by simple washing, swimming or natural perspiration; however, it only lasts for 5–7 days, as skin cells are continuously shed. Exfoliation, tape stripping, prolonged water submersion or heavy sweating can lighten the tan, since all contribute to rapid dead skin cell peeling. Indeed, users may opt to reapply the product on a regular basis in order to maintain the skin color.

Possible improvements to DHA products include: the addition of perfluoropolyether phosphate to lower the formulation’s pH; exfoliation with polyethylene beads prior to treatment; wiping skin with an acidic toner prior to application; the addition of strong antioxidants such as caffeic acid phenethyl ester; using a polymer base; and pre-treating the skin with amino acids to increase binding sites of the DHA to skin.

Organo-sulfur compounds for skin lightening: Chu et al. investigated the effects of select organo-sulfur compounds, including: 1-propylmercaptan (PM), di-methyl disulfide (DMDS), diallyl disulfide (DADS), propyl disulfide (PDS), and 2,5-dimethylthiophene (DMT) on melanin formation.⁵ The inhibitory action of the organo-sulfur compounds on tyrosinase activity and melanin formation may be attributed to a reduced formation of reactive oxygen species (ROS) and the positive modulation of the glutathion/glutathione disulfide ratio in B16 cells.