Glossary term / Chemistry
pH
A scale from 0 to 14 measuring how acidic or alkaline a solution is; 7 is neutral.
01 / Definition
Full definition
pH (potential of hydrogen) measures the concentration of hydrogen ions in a solution, running from 0 (most acidic) to 14 (most alkaline), with 7 as neutral. Healthy skin surface pH sits between 4.5 and 5.5 — slightly acidic — which supports the acid mantle and a balanced microbiome. Many actives require a specific pH range to function: vitamin C (L-ascorbic acid) needs a pH below 3.5, AHAs work optimally below 4.0, and retinoids are most stable near neutral. Products formulated outside the correct pH for their active can be ineffective or irritating.
Examples
Skin surface: pH 4.5–5.5Effective vitamin C serum: pH 2.5–3.5AHA exfoliant: pH 3.0–4.0
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