I often get product-related questions from my lovely customers and I thought they'd make great prompts for blog posts, so welcome to my new mini-series where I'll share my answers to customers' product questions, as I suspect others may find these useful!
A customer recently asked:
"I've noticed that lactic acid is listed as an ingredient in your skin quenching essence, will using this exacerbate the irritation caused by the tretinoin I'm currently using?"
This is a very sensible question to ask because I usually advise customers to avoid using exfoliating actives when their skin is adjusting to tretinoin (or other retinoids), as the skin barrier is more likely to get disrupted. However, in the case of skin quenching essence, formulation is key - it's not an exfoliating product despite the presence of lactic acid! But how is this possible?!
What typically drives the potency (and therefore likelihood of irritation) of an exfoliating acid-based product is the concentration of the acid used, as well as the pH. Products designed to encourage exfoliation tend to have a very low pH and use a reasonable amount of acid (in the case of lactic acid, usually in the 5-10% range for at-home products).
Lactic acid in particular is a multifunctional ingredient - at higher concentrations, it obviously functions as an exfoliator, but at lower concentrations (and at a higher pH), it functions as a humectant instead - hydrating the surface layer (stratum corneum) of the skin. In fact, lactic acid is naturally part of our own skin's Natural Moisturising Factors (NMF), and in our own skin it also naturally serves to hydrate (rather than exfoliate the skin).