1. Evidence for the Existence of a Self-Regulated Enzymatic Process Within the Human Stratum Corneum –An Unexpected Role for Urocanic Acid 
Paul M. Krien, Michel Kermici 
Journal of Investigative Dermatology 
Volume 115, Issue 3, Pages (September 2000)
DOI: /j x
Copyright © 2000 The Society for Investigative Dermatology, Inc Terms and Conditions

2. Figure 1
Time-dependent evolution of the proton concentration in the electrode compartment. Proton concentration is related to the pH value using the equation: C = 10–pH. A significant increase in the concentration is only observed when the tip of the electrode is in contact with skin surface.
Journal of Investigative Dermatology  , DOI: ( /j x)
Copyright © 2000 The Society for Investigative Dermatology, Inc Terms and Conditions

3. Figure 2
Influence of 15 successive tape stripping on the flux of protons in the electrode chamber. Three groups of response were observed: A partial abrasion of stratum corneum had a negligible influence on the magnitude of flux in group Slow, induced a slight decrease in group Medium, and a high decrease in group Fast.
Journal of Investigative Dermatology  , DOI: ( /j x)
Copyright © 2000 The Society for Investigative Dermatology, Inc Terms and Conditions

4. Figure 3
Evolution of skin surface pH of two volunteers after usual cleansing operation (skin washed with soap and tap water). A significant increase in the acidity of skin surface was observed with type Slow volunteers (see text for details).
Journal of Investigative Dermatology  , DOI: ( /j x)
Copyright © 2000 The Society for Investigative Dermatology, Inc Terms and Conditions

5. Figure 4
Stratum corneum pK determination via a titration curve. Titration curve was obtained after 1 h contact of water with skin surface of volunteer 21 (see Table 2). Similar titration curves were observed with all the other volunteers.
Journal of Investigative Dermatology  , DOI: ( /j x)
Copyright © 2000 The Society for Investigative Dermatology, Inc Terms and Conditions

6. Figure 5
In vivo pH gradient in human stratum corneum. Over a total of 17 volunteers, six (male) were observed in group Fast, nine (female) in group Medium, and two (male) in group Slow. The data are presented as mean ± SEM. Where no SEM is shown, the SEM was smaller than the sign of the symbol. The linear fit of data indicates a significant increase in the proton concentration with tape strip number in type Slow volunteers (R = , n = 5, p = ) and in type Medium volunteers (R = , n = 5, p = ). No significant increase was observed in type Fast volunteers (R = , n = 5, p =0.8753).
Journal of Investigative Dermatology  , DOI: ( /j x)
Copyright © 2000 The Society for Investigative Dermatology, Inc Terms and Conditions

7. Figure 6
In vivo distribution of UA in human stratum corneum. The data are presented as mean ± SEM. Where no SEM is shown, the SEM was smaller than the sign of the symbol. Over a total of six volunteers, two were observed in group 1, and four in group 2. A significant increase in the UA distribution was observed with group 2 only (R = , n = 5, p <0.001).
Journal of Investigative Dermatology  , DOI: ( /j x)
Copyright © 2000 The Society for Investigative Dermatology, Inc Terms and Conditions