46 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS extremely crude grade of petrolatum. It is also reassuring that certain lanolin derivatives such as acetylated lanolin were also comedogenic. These examples validate the specificity of the revised assay. Attention is called to the reliability of the cyanoacrylate follicular biopsy, assisted by image analysis, for identifying comedogenic substances in humans. When applied twice daily for eight weeks to the foreheads of oily, acne-prone persons, comedogenic materials such as acetylated lanolin and isopropyl myristate increased both the density and size of horny casts (unpublished observations). Thus, there is encouraging evidence that the results of rabbit and human tests are congruent. There is too little awareness that the risk of inducing comedones is concentration-dependent. Substances that are strongly comedogenic when tested neat or in high concentrations become non-comedogenic after sufficient dilution. Neat isopropyl myristate and neat acetylated lanolin are definitely comedogenic. However, the concentrations in facial products are generally well below 15%. At this level, neither agent was found to be comedogenic in either the rabbit or human model (unpublished observations). One cannot determine from a reading of the ingredients whether a given product will be acnegenic or not. What matters solely is the behavior of the product itself. In the current study both petrolatum and the 30% petrolatum emulsion product sig- nificantly reduced the number of papulo-pustules. This is a fairly typical result for non-medicated vehicles. It is of surpassing interest that in double-blind, vehicle- controlled, anti-acne studies, the beneficial effect of the vehicle often approaches that of the active agent! Mills and Kligman reviewed worldwide reports on the efficacy of dozens of anti-acne medicaments (14). There was not a single instance in which the test substance was found to be without benefit. Acne nearly always improves under medical care, regardless of the agent. This is the reason why so many marginally effective agents can be sold in large quantities. Soreness and tenderness is a frequent complaint of patients who have many inflammatory lesions. Most of the patients in this study volunteered that soreness was moderated by both products. For over a century petrolatum has been extensively used to treat a variety of skin ailments such as burns, abrasions, rashes, and dry skin. Petrolatum also has protective actions against soap and solvent damage and against irritating drugs like tretinoin (unpublished observations). These uses probably reflect its ability to enhance the barrier function of the stratum corneum and perhaps to promote healing. It has been shown that petrolatum becomes incorporated into the intercellular lipid domains be- tween corneocytes, thereby becoming part of the structure of the horny layer (15). In the original, "acne cosmetica" report, half of the cosmetics were found to be come- dogenic. This was proffered as the explanation for the relatively high frequency of acne in post-adolescent women. Several studies have shown that as many as one-third of adult women suffer from "breakouts" especially premenstrually (16,17). "Breakouts" are typical acne lesions, mostly incited by the rupture of microcomedones (18). It is now highly questionable whether cosmetics are the chief cause of post-adolescent female acne. Reputable manufacturers of a great variety of facial skin care products, moisturizers, sunscreens, foundations, lotions, and toners routinely screen their prod- ucts for comedogenicity. Women have been taught to look carefully at the label to make sure that the product is "non-comedogenic." Despite these efforts, the prevalence of post-adolescent female acne has, in my experience, increased rather than decreased (19).

PETROLATUM AND COMEDOGENICITY 47 Professional adult women seem especially vulnerable to episodic "breakouts," often lasting for decades into menopause. By contrast, ache is uncommon in post-adolescent males. I have ventured the speculation that post-adolescent female acne is due to release of androgenic corticosteroids, induced by work-associated stress, superimposed on household duties and marital commitments. The work of Lucky et al. has made it clear that the onset of acne in prepubertal girls is closely correlated with the serum level of adrenal androgens, notably dehydroepiandrosterone (20). Stress is a well known stim- ulus for the synthesis of adrenal androgens. It must also be said that genuine ache cosmetica has not altogether disappeared. There are literally hundreds of producers of cosmetic products throughout the world, and many do not adequately test their wares. I have randomly collected from the pocketbooks of my patients a surprising number of exotic skin care products by unregistered foreign manufacturers. Some of these were comedogenic in the rabbit assay. Petroleum jelly is an exceedingly complex mixture of hundreds of saturated hydrocar- bons. It is produced by the fractional distillation of petroleum. During the process, petrolatum remains in the bottom portion as a semisolid, bluish-colored material. It is then refined exhaustively to remove color, aromatic hydrocarbons, odoriferous materials, and other "impurities." Petrolatum is known generically as soft white paraffin. Speci- fications for acceptability are given in the U.S. Pharmacopea. Vaseline © is the trade- name of petrolatum made by Chesebrough-Ponds. Piewig et al. in their report on pomade ache in Afro-American males, specifically incriminated Vaseline © among other greasy grooming products (9). Herein lies an interesting story that is worth recounting. It turns out that Vaseline has become a generic term for almost any hydrophobic grease. Recently, we bought "Vas- eline" at six local pharmacies whose customers are mainly Afro-Americans. In only three stores was the product bona fide Vaseline © . The other three were Vaseline-like greases of unknown composition made by unfamiliar manufacturers. We found these three to be comedogenic in the revised rabbit model. Accordingly, in reports that incriminate Vaseline as comedogenic, one must check the source. This study is not intended as a recommendation of petrolatum for the treatment of inflammatory acne vulgaris. However, it does show the benefits of moisturization for inflammatory ache. Dermatologists routinely inveigh against oily cosmetics for ache sufferers. Patients are urged to seek oil-free cosmetics. This advice has not been supported by scientific studies. Comedogenicity has nothing whatever to do with oiliness the latter is a physical attribute and not a chemical entity. Some of the most potent comedogenic substances, dioxin for example, are non-oily. On the other hand, many classical oils, notably vegetable oils, are usually non-comedogenic. Chemical structure determines comedogenicity. As yet, acnegenicity cannot be pre- dicted by structure. The mechanism underlying comedogenicity is unknown. Why corneocytes stick to each other to form horny impactions is still a mystery. REFERENCES (1) A.M. Kligman and O. H. Mills, Ache cosmetica, Arch. Dermatol., 106, 843 (1972). (2) A. Zatulone and N. A. Konnerth, Comedogenicity testing of cosmetics, Cutis, 39, 591 (1987).