Skin Chakra has a detailed post all about this; I highly recommend reading it.
In that post she demonstrates that the pH of diluted samples does not start to drift towards the pH of the diluent (distilled water) until the dilution dips below 10%.
That diluting a formulation by 90% wouldn’t meaningfully alter the pH rather defies logic, so I did a similar experiment. I created 10%, 20%, 30%, 40%, and 50% dilution testing solutions of a formulation. I also tested the formulation at 100% concentration as it was thin enough to do so.
I took multiple readings for each solution, averaged them, and plotted them on a graph.
The difference between the 10% dilution and the pure product was less than 0.1 pH point. Creating a 10% dilution of your formulation does not meaningfully alter the pH reading you’ll get. You could test any level of dilution above 10% if you were so inclined and get nearly identical results; 10% simply wastes the least amount of product.
Still skeptical? Try it yourself!
Posted in: Measurements