88 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS ..½.•-&:. . .- . . •: . ......:,::.•, . ,• .• ,•,. .... . ..x.: . ,. • • ... ,,., ...• .• .:. •'•'.: . •'• ½'h.:.¾•- . .•-• "-:'}..:: .½.:-•m • ...... •,,.. , ...•. ......... •, .. %- :. ., '•*• .:.•.• . ,....½-' :' Figure 6. The alkali swelling technique illustrating the dandruff horny layer with its chaotic patterning, crevices, and buckled, poorly swollen cells plasia (b) extensive parakeratosis, and (c) signs of inflammation, includ- ing a dermal infiltrate with migration of lymphocytes and histiocytes into the epidermis (exocytosis) (2). The focal nature of the parakeratosis in dandruff is worthy of empha- sis. This finding perhaps provides some insight into the pathophysiol- ogy of dandruff. As a rule, parakeratosis is a sign of increased epider- mal turnover the cells stream so rapidly to the surface that they do not have time for keratinization to be completed. The focal parakeratosis in dandruff suggests that the rate of epidermal growth is not uniform. Some microscopic segments are turning over at a faster rate than others. This, in turn, might lead to the uneven disruption of the dandruff horny layer and to the production of thick masses of horny cells in some places while elsewhere the horny layer is not thickened and, in fact, may be thinned.

OBSERVATI()NS ON I)ANI)RUFI• Nondandruff horny layer visualized by the sodium hydroxide swelling method. The cells are coherent, well swollen, and regularly patterned Organization of the Horny Layer Cellular Number That the number of cells in the dandruff intact horny layer is fewer than normal was demonstrated by two methods: A. Scotch Tape Stripping--After shaving the scalp, the number of strips required to reach the glistening layer was determined in 5 dandruff and 5 nondandruff subjects. The end point was reached much earlier in dandruff. The number of strips was 10 to 15 in dandruff, compared to 26 to 48 in the nondandruff. This suggests a lesser number of cell layers in the coherent stratum corneum or that more cell layers were removed per strip in dandruff. B. Sodium Hydroxide Swelling--Sheets of horny layer obtained by the cantharidin blister technique (3) were sectioned and the cells rendered visible by swelling with sodium hydroxide (4). Eight dandruff and eight nondandruff horny layers were so studied.