Preparation and evaluation of cosmetic patches containing lactic and glycolic acids

Background: Alpha-hydroxy acids such as glycolic acid (GA) and lactic acid (LA), are used in cosmetic patches. The important fact in cosmetic patches is its suitable adhesion and peel properties.
Aim: The objective of this study was to prepare LA- and GA-containing cosmetic patches and evaluate in-vitro/in-vivo correlation of adhesion properties.
Methods: Pressure-sensitive adhesives with different concentrations of GA and LA were cast on a polyethylene terephthalate film. The patches were evaluated for peel adhesive strength. On the basis of in vitro adhesion properties the patches were selected for wear performance tests and skin irritation potential.
Results: The adhesion properties (adhesion to steel plate and skin) and cohesive strength tests indicated the substantial influence of GA and LA concentrations. Based on in vitro adhesion studies the patches containing 3% (w/w) GA were selected for in vivo studies. In vivo studies show that a formulation containing 3% GA displays good adhesion on the skin, but it leaves little residues on the skin. Skin Irritation studies on healthy human volunteers showed negligible erythema at the site of application after 48h.
Conclusion: The noninvasive patch test model was found useful for detecting irritant skin reactions to the cosmetic patch containing GA. Our results demonstrated a strong correlation between the adhesion to steel plate and adhesion to skin. But a weak correlation between the degree of adhesive residue on the skin in in vitro and in vivo tests was observed for the formulation containing 3% (w/w) GA.

Keywords
Cosmetic patch, Glycolic acid, Lactic acid, Peel adhesive strength, Pressure-sensitive adhesive, Tack