Why does an exfoliating toner need such a low pH?
Short answer
Salicylic acid only exfoliates below pH 4.5, so the toner is set at 3.8–4.2. Lactic acid and Azeclair also work better in acidic conditions.
Explanation
The book's toner combines witch hazel, peppermint and rose hydrosols with Azeclair, sodium lactate, panthenol and 0.5% salicylic acid. It's aimed at oily and problem skin and isn't suitable for dry skin.
What to do
- Pre-dissolve Azeclair and salicylic acid in 5–10 g of warm hydrosol before adding the rest.
Source: The Big Book of Homemade Skin Care — Clarifying Bio-Balance Toner