pH
A measure of acidity. Skin sits at 4.5-5.5; most leave-on products target 4.5-6.
pH (potential of hydrogen) is a scale from 0 (very acidic) to 14 (very alkaline), with 7 being neutral. Skin naturally sits in the slightly acidic range of 4.5-5.5 — what is called the “acid mantle.” Products that respect this range tend to feel comfortable, work well, and not disrupt the skin barrier.
General targets for DIY formulations:
- Leave-on products (creams, serums) — pH 4.5-6
- Rinse-off cleansers — pH 4.5-6 for face, slightly more flexible for body
- Vitamin C (L-ascorbic acid) serums — pH 3-3.5 to keep the active form
- Salicylic acid for exfoliation — pH 3-4
- Shampoos — pH 5-5.5
Always test with pH strips or a meter — many ingredients shift the pH of the finished product in unexpected ways.