To download a pdf version of the image below, click on the following text: AHA Free Acid Value Infographic
Let’s walk through an example using the “Glycolic Acid Example” table in the infographic above.
If you know that Pixi Glow Tonic has an advertised concentration of 5% Glycolic acid and a pH of 4.0 (assuming that you either knew this because you measured the pH or because you used the excel spreadsheet to find out), looking at the table above, you can know that it only has 40% Free acid overall (which is below the recommended amount of 50-75%) and it has a free acid value of 2.0%. So *the glycolic acid* in the Pixi Glow Tonic will offer moisturization (and would be good as a pH-adjusting toner). But this is where looking at the other ingredients also comes into play. So you would need to look at all the ingredients to get a better sense of how exfoliating it would be, and the effect it would have on your skin. The free acid value helps you to evaluate the potential efficacy of just the AHA portion of the ingredient list.
The Pixi Overnight Glow Serum with 10% Glycolic acid has a different result. It has been reported that it has a pH of 3.0, so it has 87% Free acid, which is above the minimum threshold of 50-75%, and it has a FAV of 8.7%. So it is capable of providing moisturization, a significant increase in glycosaminoglycans, a significant amount of cell turnover and a moderate increase in collagen deposition. But since it is a stronger acid, with a lower pH, you may experience some irritation. Listen to your skin and start slow when incorporating this acid in your routine.
***This series on Free Acid Concentration would have taken me A LOT more time had it not been for the amazing resource (the Free Acid Calculator) that Lab Muffin provided on her blog: http://www.labmuffin.com/free-acid-calculator-for-exfoliants-at-specific-ph-levels/
She is incredibly knowledgeable and has great Instagram and Blog posts. The free acid calculator is an invaluable resource–bookmark it and use it! 🙂
Here is the complete Excel spreadsheet that I will update as I receive more information from companies, or tips from you all!
Click Here –> AHA Product Comparisons
Important Things to Note:
- When companies listed a range of pH values, I went with the high end of the range.
- Note: This ONLY focuses on the percent of the featured AHA. It is important to also look at the complete ingredient list as some products might include other ingredients that could help reduce irritation, increase irritation, or provide additional benefits other than exfoliation.
- A percentage may be listed in the name of the product, but that doesn’t indicate it’s free acid value. I left those percentages in so that you could find the correct product as some names only change in terms of percent acid (e.g., Garden of Wisdom Mandelic Acid 15% vs. Garden of Wisdom Mandelic Acid %10 Serum).
- In products with blends, the pKa for the first acid listed in the ingredient list was used to calculate the free acid value.
- If formula’s change, the pH may change as well. Also, some countries may have slightly different formulations, so it is always beneficial to pH test your own products. For some pH strips and meters see this post.
pH value color key:
- Red = value provided by company
- Blue = value provided by Beautypedia
- Green = value provided by bloggers/reddit
- Purple = value provided by my own pH meter