Measuring human skin buffering capacity: an in vitro model.
OBJECTIVE
It has been thought that skin possesses buffering capacity. This study measured the skin buffering capacity against two model solutions of acid and base at three concentrations with an in vitro system.


METHODS
Ten microliters of model base (sodium hydroxide--NaOH) and acid (hydrochloric acid--HCl) solutions at concentrations of 0.025, 0.05, and 0.1 N was applied to human cadaver skin (3.18 microL/cm(2)) placed onto glass diffusion cells. Phosphate-buffered saline (PBS) was used as a standard buffer solution. Deionized water served as the negative control, whereas untreated skin served as the blank control. Skin pH was read and recorded immediately following dosing (0 time), and at 10 and 30 min of post-dosing. After the 30 min of dosing, each skin, except untreated skin (blank control), was then washed by applying 1 cm(3) of deionized water. The pH on each washed skin was measured immediately following washing, and the pH measurement was repeated at 10 and 30 min of post-washing. Six replicates were conducted.


RESULTS
The pH values sharply significantly increased (P<0.05) immediately following dosing with NaOH at all concentrations (the highest concentration, caused the highest pH), and then decreased closely to baselines within 30 min post-application but still remained at significantly (P<0.05) higher values when compared with the blank control (untreated skin). HCl (acid) significantly (P<0.05) decreased skin pH immediately following dosing with all concentrations (the highest concentration, caused the lowest pH) and then restored rapidly to baseline. There was no significant difference in post-washing procedures on the skins that were pre-treated with the acid (HCI) solutions. However, with all base solutions (NaOH) pre-treated skin, pH values were significantly higher (P<0.05) at all time points post-washing. Furthermore, both PBS and water controls significantly elevated (P<0.05) the pH values following washing.


CONCLUSIONS
Skin pH and its buffering capacity can be measured on human cadaver skin in vitro, which may partially replicate the response of in vivo skin. Dose-response was noted; i.e. the higher concentration caused larger changes in skin pH. In addition, the restoration of skin pH is relatively faster with acid when compared with base treatment. Clinical implications are offered.
Zhai
Hongbo
H
Department of Dermatology, School of Medicine, University of California, San Francisco, CA 94143-0989, USA.
Chan
Heidi P
HP
Farahmand
Sara
S
Maibach
Howard I
HI
D000136:Acid-Base Equilibrium / Q000187:drug effects / Q000502:physiology*; D002021:Buffers; D004305:Dose-Response Relationship, Drug; D006801:Humans; D006851:Hydrochloric Acid / Q000494:pharmacology*; D006863:Hydrogen-Ion Concentration / Q000187:drug effects*; D066298:In Vitro Techniques; D008954:Models, Biological; D012867:Skin / Q000187:drug effects / Q000378:metabolism*; D012882:Skin Tests; D012972:Sodium Hydroxide / Q000494:pharmacology*
D002021:Buffers; D012972:Sodium Hydroxide; D006851:Hydrochloric Acid