pH

What It Is

A logarithmic scale from 0–14 measuring the acidity or alkalinity of a substance. Skin's natural surface pH is approximately 4.5–5.5 (mildly acidic). Many actives have strict pH requirements: AHAs and BHAs require pH 3–4 for exfoliating activity; L-Ascorbic Acid requires pH below 3.5 for stability and absorption; copper peptides (GHK-Cu) are destabilised by low pH. Products with incompatible pH levels can neutralise each other's efficacy when layered immediately together.

Key Context

If layering pH-sensitive actives, apply the lowest-pH product first and wait 20–30 minutes before applying the next, to allow the skin's buffering capacity to partially restore. Or separate acids/Vitamin C (AM) from copper peptides/retinoids (PM).

Learn More

• How to Start Using Acids
• Copper Peptides vs Vitamin C
• Ingredient Combinations to Avoid