pH is not a term that comes up often in consumer skincare conversations, but it should. It has a direct effect on how products work, how the skin barrier functions, and whether ingredients that are supposed to be active actually are.
pH is a measure of acidity or alkalinity, on a scale from 0 (most acidic) to 14 (most alkaline), with 7 being neutral. Healthy skin surface pH sits between approximately 4.5 and 5.5 — mildly acidic. This acidity is maintained by what’s called the acid mantle: a thin film of sebum, sweat, and microbial metabolites that sits on the skin surface.
The acid mantle matters for several reasons. It inhibits the growth of pathogenic bacteria and supports the growth of the skin’s beneficial microbiome. It activates the enzymes responsible for barrier lipid processing. And it influences how quickly the skin can recover from disruption.
Products that are significantly more alkaline than the skin surface — many traditional bar soaps sit at pH 9–10 — temporarily disrupt the acid mantle and raise skin pH. This impairs barrier function, inhibits the enzymes that process ceramides, and creates conditions in which pathogenic bacteria can proliferate more easily. The effect is temporary in healthy skin, but cumulative disruption contributes to sensitisation over time.
For the oil-based products in the Oath Co range, pH is less critical than for water-based formulations — anhydrous (water-free) formulas don’t have an aqueous pH in the traditional sense. But pH becomes relevant when our products interact with the skin’s existing acid mantle, and in the aqueous components of ingredients like niacinamide and centella asiatica extract. We formulate with this in mind, ensuring that the base in which these ingredients are delivered doesn’t work against the acid environment in which they’re most effective.
For everyday skincare decisions: use gentle, pH-appropriate cleansers. Avoid bar soap on the face. And if a product is making your skin feel tight and stripped after use, the pH may be the reason.