330 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS OLETH-iO OLETH. 2 Figure 4. Oleth-3 compared to oleic acid. The initial additions of ethylene glycols to potentially comedo- genic and irritating ingredients appear to increase this propensity. Further additions of ethylene glycols, such as oleth-10 and oleth-20, tend to reduce reactions. Some ingredient combinations--for example, the combination of glyceryl stearate with potassium stearate (available commercially as glyceryl stearate S.E.) and also the combi- nation of D&C red #36 and mineral oil--appear more comedogenic than the indi- vidual compounds themselves. These synergistic reactions need to be studied further.

COMEDOGENICITY 331 Table II Comedogenicity of D&C Red #36 Dye in Different Vehicles Grade (0- 5) Comedo. lrrit. D&C red #36 in mineral oil D&C red #35 in pentaerythrital tetra caprdcaprylate D&C #36 in propylene glycol D&C red #36 in PEG 400 3 0 2 0 1 0 0 0 The opposite is also possible. For example, the combination produced by the ingredient D&C red #36 and the vehicle polyethylene glycol is less comedogenic than D&C red #36 when incorporated into other vehicles. The cosmetic chemist may be able to take advantage of these findings in the future to custom design noncomedogenic products. SUMMARY These studies indicate that skin care preparations that are nonirritating and noncome- dogenic can be made. Nonreactive ingredients can be used to make elegant products, and borderline ingredients can be combined with other ingredients to reduce the reac- tions to acceptable levels. In spite of these guidelines, new formulations must always be examined with the rabbit ear assay before the cosmetic chemist can be assured that his ideas work. Figure 5. The comedogenicity of D&C red #36 when incorporated into two different vehicles. The ve- hicle may increase or decrease an ingredient's ability to produce follicular hyperkeratosis.