L-Arginine as a pH Booster

Dear Valerie: I realize L-Arginine is not the most potent, efficient or most cost-effective method of increasing a product’s pH, but if input costs are not a hindrance, and a relatively small pH up shift is needed, especially in the light of trying to formulate naturally, what are your thoughts on using L-Arginine?  — Basic Bill

Dear Bill:

You hit the nail on the head! Using L-arginine to adjust pH isn’t the most potent, efficient or cost-effective method of increasing pH, but it does work. If you can afford it, your formulation can tolerate it, and you have an understanding of chemistry, you should use it without fear of condemnation. However, I would focus on those parameters in a very different order—compatibility first, performance second, affordability third.

Arginine is not compatible with all systems. Arginine is a basic amino acid with an extremely high pKa (for an amino acid); studies estimate it to be anywhere from 12 to 13.8. This means that at any pH below this pKa, arginine will have a positively-charged side group. Your thickeners, emulsifiers and any other actives must be cationic-friendly. This makes it great for haircare since formulations typically use cationic materials. But in skincare, one must adjust the formulation to ensure anionic thickeners or emulsifiers do not interfere. Once you have cleared this hurdle, employing arginine for pH adjustment wreaks less havoc in your system.

Cationic materials also stick to negatively-charged keratin, which is the predominant protein composing skin and hair. This is good news for hair, since we want cationic materials to stick to hair and supply some sensory attribute. While skin is less anionic than hair, it still has a negative charge, and this means arginine can impact the haptics of a formula. I’m personally not a fan of the sensory cationics impart on skin, but some people like them. Test it out, in case there is some effect.

What do I mean by affording it? Compared to other conventional pH boosters, like sodium hydroxide or triethanolamine, arginine is more expensive from a cost-per-pound perspective. It does require higher use levels than sodium hydroxide, as well, depending on what you’re adjusting. This significantly compounds the increase in cost-per use. However, any good formulator worth their salt can work around this if the product’s marketing department requires the appeal of arginine.

I’d also like to clear up a couple misconceptions about arginine. It is NOT a drop-in replacement for sodium hydroxide or other pH adjustors. It is a unique additive that must be used thoughtfully. While it has a high pH, it might not contribute the necessary alkalinity if using it to neutralize other ingredients. Check with your ingredient suppliers if this is a requirement! Also, conduct stability on your formulations (as you always should) to check for pH drift. I don’t expect pH to drop (there is some interesting literature about arginine in oral care and it holds pH in bacterial films),¹ but there are many other aspects that arginine brings to the formulation that require scrutiny.

Lastly, I’ve seen chatter about avoiding use of arginine in formulations to reduce the risk of nitrosamines or Schiff bases. This isn’t really an area of concern. Arginine isn’t a secondary amine; thus, any catalysis of nitrosamine formation is extremely low. There are other formulation elements that must be present for nitrosamine formation to occur. If you are concerned about nitrosamine formation, employ the use of nitrosamine inhibitors in your formulation. For Schiff bases, employ the use of a chelating agent, which you should be doing anyway.

There you have it. If you like, can afford, and have the know-how to formulate with arginine, use it!

References:

1. Agnello, M., L. Cen, N.C. Tran, W. Shi, J.S. McLean, and X. He. “Arginine Improves pH Homeostasis via Metabolism and Microbiome Modulation.” Journal of Dental Research 96.8 (2017): 924-930.

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