Skin can Modulate the pH of Topical Creams and Gels

The pH of the formulation can affect the pH of the skin surface. However, the skin's pH is known to recover rapidly due to the substantial buffer capacity associated with the skin. The objective of the project was to investigate the effect of the buffer capacity of skin on the pH of the formulation. A few custom-made gel and cream formulations were used as test products in the study. Custom-made gel and cream formulations were prepared and applied to human skin, with parallel applications on an inert substrate serving as controls to isolate the effect of solvent evaporation. In the control group, pH changes due to evaporation were negligible across all formulations. In vivo application revealed that the skin's buffering capacity significantly modulates the pH of the applied formulation. When formulations had a pH higher than the skin's basal level, the skin responded by reducing the formulation pH. For instance, a cream adjusted to pH 9 showed a drop of more than one pH unit within 30 min post-application. Conversely, formulations with pH lower than the skin's baseline exhibited an increase in pH; creams adjusted to pH 4 increased by over 0.5 units in the same timeframe. This bidirectional shift highlights the skin's active role in restoring pH homeostasis. The incorporation of buffers with varying ionic strengths into the formulations reduced the extent of pH drift, offering greater resistance to skin-driven pH changes compared to unbuffered formulation.