Downward pH Drift

Dear Valerie: I’m experiencing downward pH drift in a facial cleanser and wonder what is the best way to address this issue?  —Alkaline Alan

Dear Alkaline:

I love it when pH drift occurs completely inside a finished product specification range. There is a feeling of power. Do I fix it, or not? What’s not so fun is having pH drift outside of your specified range.

Fortunately, this can easily be solved by creating a buffer system. You may remember buffers from high school biology or college chemistry. Or, you may not, like one of my former chemists who was once perplexed at my request to add a phosphate buffer in a shampoo that had these same issues. 

A buffer system is essentially a weak acid and corresponding conjugate base that allows for continual shift in equilibrium between an acid and a base. The net result is virtually no shift in pH because you always have a little acid and a little base. For example, if using lactic acid to lower pH, I would add its corresponding salt, sodium lactate. For a cleanser, I would create a phosphate buffer. 

The rule of thumb for selecting a buffer system is the pH of your final product. If around a neutral pH, elect the phosphate buffer; at a lower pH a lactic or citrate buffer system. Appropriate ratios are readily searchable online. You want to add the same amount of buffer to your formulation, every time. They should not be treated as pH adjusters, per se.

Speaking of pH adjusters, I found that triethanolamine always led to better pH stability in cleansers than adjusting with sodium hydroxide. It’s a shame no one likes TEA anymore—no one being clean beauty retailers or California’s OEHHA, keepers of the Prop 65 list. Hopefully this gives you a little more stability!

Valerie George is a cosmetic chemist, science communicator, educator, leader, and avid proponent of transparency in the beauty industry. She works on the latest research in hair color and hair care at her company, Simply Formulas, and is the co-host of The Beauty Brains podcast. You can find her on Instagram at @cosmetic_chemist or showcasing her favorite ingredients to small brands and home formulators at simply-ingredients.com. Her email is: askvalerie@icloud.com