Why is pH important in skincare?
Short answer
Healthy skin's acid mantle sits at about pH 4.5–5.5. Products in that range protect the barrier, and pH also decides whether some actives and preservatives work.
Explanation
Alkaline cleansers damage the skin barrier and leave it dry and vulnerable, so the book's cleansers and shower gel sit at pH 4.5–5.5. A lower pH also helps preservatives work better. Some actives need a specific window: salicylic acid only exfoliates below pH 4.5, which is why the toner targets 3.8–4.2, while copper peptides are sensitive to pH jumps and the serum sits at 6.0–6.5.
The book's targets: cleansers 4.5–5.5; barrier cream 4.8–5.2; exfoliating toner 3.8–4.2; copper-peptide serum 6.0–6.5; firming gel 4.2–5.0.
What to do
- Check pH after the preservative is in and the product has cooled.
- Adjust drop by drop: a 10% citric or lactic acid solution lowers pH, and a 10% sodium hydroxide solution raises it.
Source: The Big Book of Homemade Skin Care — Calming Chamomile Foam Cleanser · Clarifying Bio-Balance Toner · Gentle Shower Gel with Physiological pH