Читать книгу pH of the Skin: Issues and Challenges - Группа авторов - Страница 76

The application of a drop of acid or alkaline (pH 10) liquid resulted in a quick color change for the uncoated pH paper. In the lower part of the picture, which was coated with emollient, the pH paper behaved differently (Fig. 4). The liquid did not spread and change color on the paper. The emollient was an effective short-term barrier to penetration of an aqueous solution into the paper. Acidic and basic solutions applied to pH paper with and without emollient demonstrated barrier effect.

Fig. 9. Measuring the surface pH of collagen skin-mimic film while the opposite side of the collagen skin-mimic film is in contact with buffer pH = 10 solution. Experiment measured the barrier effect of emollient on the skin mimic.

In the study of the test subjects in our laboratory, prior to emollient application, pH of the skin was 4.96 ± 0.30 (mean ± SD). After emollient application, the measured pH rose to 6.20 ± 0.32 (mean ± SD). This is the same as the pH of the electrode rinse solution, which was measured at 6.30. This confirmed the findings of the previously completed clinical studies and showed that the pH skin effect was due to emollient, which was easily reproduced in the lab. Adding a drop of dilute citric acid on top of the emollient area on the subject’s skin caused the measured pH to drop to 2.8. This showed that acid on the surface of the emollient could be measured with the pH probe. This low pH indicates that the emollient is not highly buffered and does not change the pH of the citric acid applied to the emollient surface.

This previous experiment was done in reverse order. When a drop of lime juice was placed on a fresh area of forearm skin, the measured skin pH reduced to 3.5. Then, this area was covered with emollient, and the superficial pH rose above pH 6. This demonstrates that either the emollient served as an effective barrier once covering the lime juice or else the emollient contains a chemical that can neutralize acid. A separate experiment described later in this chapter was done to prove that the emollient does not increase the pH of aqueous liquids in contact with the emollient. So, the emollient is acting as a barrier.