At highest concentrations (50-70%) applied for 3 to 8 minutes under the supervision of a physician, glycolic acid promotes slitting between the cells and can be used to treat acne or photo-damaged skin (e.g. due to mottled dyspigmentation, melasma). The benefit of such short-contact application (chemical peels) depends on the pH of the solution (the more acidic the product, or the lower the pH, the more pronounced the results), the concentration of GA (higher concentrations produce more vigorous response), the length of application and prior skin conditioning such as prior use of topical vitamin A products. Although single application of 50-70% GA will produce beneficial results, multiple treatments every 2 to 4 weeks are required for optimal results.