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To test the emollient barrier hypothesis, we first compared the behavior of a pH indicator paper coated with emollient to the behavior of uncoated indicator paper (Fig. 4). We then applied the emollient to a portion of the forearm of test subjects (n = 4) in our laboratory. This experiment was also performed in reverse order, where a drop of lime juice was placed on a fresh area of forearm skin and then this area was covered with emollient and the pH measured. A total of 13 sites were used (Fig. 5, 6).

To visually demonstrate the effect of the emollient barrier, an innovative technique was used where blackberry juice was applied to the forearm as a natural pH indicator. As pictured in Figure 7, half of the berry juice-dyed skin was covered with emollient, and the other half remained intact. Then, a drop of highly alkaline aqueous solution was placed on each half. Berry juice dye is red at acidic pH and turns blue when the pH is above 7 (neutral), and this is what happened on the skin not protected by the emollient. On the side where the emollient was applied (upper part of Fig. 7), alkaline aqueous solution was stopped by the emollient barrier and did not change the color of the berry juice on the skin. This demonstrated that the emollient creates a protective barrier that can help skin maintain a healthy, low pH, even in the presence of an alkaline chemical irritant.

Fig. 6. Close view of a rinsed glass electrode about to make a skin pH measurement. The image on the right shows the electrode being lifted from the skin and the small amount of aqueous solution that is between the glass electrode and skin during the pH measurement.

Fig. 7. Emollient visualization of barrier effect of emollient on human forearm skin using blackberry juice. Blackberry juice was applied to the forearm as a natural pH indicator to demonstrate visually the effect of the emollient barrier.