THE NATURE OF DANDRUFF 123 VII. Tnr• Covns• or DAN•)nUFr We had the opportunity to follow institutionalized dandruff subjects in- cluding young adults and the elderly for a year or more. The scalps were as- sessed both by clinical grades and by corneocyte counts. Apart from the already mentioned seasonal variations, we have come to the conclusion that dandruff is a rather stable process. Counts and grades vary little over many months. The extraordinary week to week oscillations in the severity of dandruff reported by Van Abbe and Dean are outside our ken (4). We regard scaling to be about as steady a process as sebum excre- tion or hair growth rates, although more easily modified by external factors. As we see it, once an individual develops dandruff he will have to live with it till old age slows down epidermal proliferative activity. Dandruff does not come and go, folklore notwithstanding. The saying, "getting ones dander up" applies not to dandruff, but to seborrheic dermatitis, an unrelated con- dition. It should be pointed out that the corneocyte counts are likewise quite sta- ble. It would appear that the rate of production of horny cells and scales is a rather fixed characteristic as typical of an individual as his complexion or body odor. VIII. Is DANDRUFF A DtSEASE? A disease exists when there are structural or behavioral changes, which are qualitatively different from the nornaal, a distinction that is not always easy to make. The finding of tissue pathology, gross or microscopic is decisive. As we now conceive the process, dandruff is not a disease in the visual sense. No feature can be found which is absent in "normals." The differences are purely quantitative. People with dandruff make more horny cells and more scales. Desquamation is a physiologic process individuals are distribut- ed along a continuum depending on rates of shedding. There can be no sharp dividing line between dandruff and nondandruff subjects. As with all physiologic processes, the population can be fitted into the normal bell shaped curve. Using corneocyte counts, we have shown that the rates of horny cell production are log normally distributed, that is, a bell shaped curve is ob- tained when frequency is plotted against the log of the corneocyte count. Accordingly, the averages are expressed as geometric means rather than arithmetically. For statistical analysis, the values must first be transformed into logs. People with dandruff are located to one side of the bell shaped curve. The proper terminology is not dandruff versus "normal," but dandruff ver- sus nondandruff. Where the line is drawn is, of course, quite arbitrary. Since dandruff is only an intensified state of desquamation and scaling, it

124 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS is altogether inept to speak of "cures." Dandruff can be suppressed but how can a physiologic process be cured (except by death! ). Virtually, nothing is known of the mechanisms, which regulate the rate of epidermal proliferation. Current theories focus on chalones (inhibitors of cell multiplication) and cyclic AMP. Turnover is increased when the concen- tration of the latter is low. No measurements of these regulators have been made on the scalp. We have cursorily looked into the question of whether or not dandruff subjects have increased epidermal turnover in other body areas, the trunk for example. Dandruff subjects give no clinical evidence of increased shedding such as fine scaling, dryness, or roughness. Bearded subjects did not have dan- druff in the beard area. The labeling index was determined on the back and thighs of 4 subjects with severe dandruff. The proportion of DNA synthesiz- ing cells was within the normal range. It is probable that increased des- quamation is limited to the scalp. Finally, it seems unlikely that an animal model of dandruff can be ex- perimentally created. Definitions are all important here. The appearance of dandruff is easily mimicked. Scaling is a nonspecific response to injury. Chem- ical and physical trauma will provoke increased cell turnover and desqua- mation of horny cells in flakes, a dandruff-like condition. Histologically, how- ever, one sees the stigma of tissue injury: inflammatory cells and thickening of the epidermis. In Troller's guinea pig model, the scaling, which followed inoculation of Pityrosporum ovaIe onto skin, anointed with artificial sebum was, in our view, no more than an irritant response to substances liberated from the fatty mixture (8). Rubbing 10 per cent lauric acid in mineral oil daily over the flank of a gninea pig will also induce scaling. Histologic ex- amination immediately shatters the idea that the process is equivalent to dandruff. The telI-tale signs of skin iniury are vividly displayed in the micro- scope. On the other hand, we know of no reason why dandruff should not occur spontaneously in furry animals. Many pet owners think that dogs have dan- druff! IX. Is DANDRUFF A M•LD FORM OF S}mORRm •c DERMATITIS. 9 The statement that dandruff is grade one-half seborrheic dermatitis is trenchant but untrue. These conditions have little in common save scaling. Seborrheic dermatitis is an inflammatory process with a recognizable histolog- ic pattern. As a rule, seborrheic dermatitis will generally show its typical greasy scales on the face and so can easily be recognized. Moreover, unlike dandruff, it is a fluctuating process often being aggravated by emotional stress. There is a widespread, but nonetheless false belief, that dandruff is patchy, involving some portions of the scalp more than others. This idea has resulted