Cleopatra’s Skincare Routine

Dear Valerie: What do you think of fermented milk-based products touted as exfoliants? They claim to have a lactic acid, which does the exfoliating.  —Sour Sam

Dear Sam:

We have all heard the story that Cleopatra bathed in sour milk, which was the secret to her beauty. I would like to think it was the lipids and proteins present in milk, not any significant quantities of acids. 

This was also a question in 2019 on my podcast, The Beauty Brains. I spent some time researching the lactic acid content of fermented milk. I managed to find my scribbled notes, which don’t have any references. Nonetheless, regular fermented milk has around 0.3% titratable acidity, while kefir and yogurt are around 0.6%. Pretty low!

Furthermore, the pH of milk is around 6-6.5. Since the pKa of lactic acid is just under 4, this means the lactic acid in your dairy is all just about in the lactate form. Unless you’re using spoiled milk, which is curdled. That has a pH closer to 4, which would presumably have a pinch more lactic acid present (if you count 0.3% as a pinch more). It may be better for exfoliating your skin—if you can stomach the smell.

This is where I think people really give a free pass to the Cleopatra claim—unless spoiled milk was considered a tolerable odor back then. I just don’t believe that even three thousand years ago she was submerging herself in that fetid curdle! Me? I’m going to stick to my traditional exfoliants and consider hydrolyzed milk protein. Tri-K has a wonderful one that does a really great job, no foul odor!

Valerie George

askvalerie@icloud.com

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