This is from the DECIEM website:
"pKa is the most important aspect to consider in formulating with acids. pKa implies acid availability. When pKa is close to pH, there is an ideal balance between salt and acidity, maximizing effectiveness of the acid and reducing irritation. Higher pH numbers in such a case would increase salt which counter-intuitively would make the formula even more irritating than if the formula was more acidic."
So, Glycolic Acid (pKa 3.6) is less irritating at pH 3.6 then at pH 4.6?