COMEDOGENICITY 327 Figure 1. The key ingredient is acetylated lanolin alcohol -- cetyl acetate--is not only comedogenic, but it is also an irritant. Similar analogies are apparent with the alcohols, ethers, glycols, and sugars. Short- chain alcohols do not cause a reaction. The mid-chain-length alcohols are comedogenic and more irritating than their fatty acid analogs (Figure 3). In the glycol series, as the hydrocarbon component becomes more dominant, the compound is more effective at producing comedones. The pure sugars are noncomedogenic. However, if they are com- bined with penetrating fatty acids, they may become follicular irritants. Also, if they are combined with another irritant, as in glyceryl stearate (SE), which contains added sodium or potassium stearate, the combination becomes more comedogenic. The in- creasing addition of polyethylene glycols to the fatty acids increases the HLB balance, reduces the follicular irritancy, and appears to prevent hyperkeratosis. An example is the oleth 3, 5, 10, 20 series (Figure 4). Among the waxes, the hydrocarbon chains appear too long to penetrate unless the wax is modified, such as in sulfated jojoba oil. In the case of beeswaxes and jojoba oils, some commercial preparations are more comedogenic than others. This suggests more con- taminants or irritants in some of the preparations. Emulsifying wax NF may be irri- tating, depending on the concentration of longer-chain alcohols such as cetearyl al- cohol. Chemicals such as cellulosic polymers, the silicates, and the carbomers used in the pharmaceutical and cosmetic industry to thicken lotions and creams are not usually a problem. The clays, bentonite, and kaolin are also not a problem. Neither is talc. Clinically, natural oils such as cocoa butter and coconut butter have long been known to cause problems with pomade acne. This is confirmed in the rabbit ear assay. Also,

328 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS ISOPROPYL MYRISTATE - OCTYL DODECYL STEAROYL STEARATE Figure 2. Ingredient testing in the rabbit ear assay--the macroscopic view of the results from testing isopropyl myristate. Microscopic examination confirmed the comedogenicity seen visually. Note that the ingredient is also an irritant compared to a potential substitute, octyl dodecyl stearoyl stearate. hydrogenated vegetable oil (Crisco ©) appears to contain residual irritating lipids. Among the natural oils such as sesame oil, avocado oil, and mink oil, the results are improved when a more refined oil is used. However, it seems easier to use safflower oil and sunflower oils, which are naturally less comedogenic. Mineral oil presents a com- plex problem: some sources are acceptable others are not. D&C red colors represent a perplexing mixture of different types of red dyes and pig- ments. Some are mildly comedogenic others are not. The common pigments used in powder blushers (D&C red #6, barium lake D&C red #7, calcium lake and D&C red #9, barium lake) are relatively noncomedogenic. However, the vehicle is also particu- larly important for the D&C red colors. A dry compressed powder or powder suspended in an evaporating vehicle such as propylene glycol may be noncomedogenic. The same dye incorporated into a nonevaporating oil can be comedogenic (Table II, Figure 5). Carmine, which is a red dye obtained from insect wings, is noncomedogenic and may be used as a substitute. The iron oxides, chromium hydroxide, and titanium dioxide are not a problem. The silicones and steroIs do not appear to be a problem. Among the vitamins, tocoph- erol is a follicular irritant. Tocopherol has been advocated by the layman for years to increase wound healing and reduce scar formation. However, it should not be used on acne-prone skin because of its potential to produce follicular hyperkeratosis. The deriva- tive, tocopheryl acetate, is noncomedogenic, and research needs to be done to see if it is an acceptable substitute.