—BUGS BONNIE

Dear Bugs:
Maybe, maybe and maybe! This is an excellent question that often finds our fellow comrades divided. Devout antimicrobialists may tell you to juice every product with a preservative or pseudo preservative to keep microorganisms at bay. Others will preach that anhydrous materials can’t support microbial growth, and therefore adding another chemical isn’t necessary. I’m not standing on either side of the fence—in fact, you can find me perched right on top, in the middle. You see, it’s not quite that simple.

We typically assess the need for a preservative when considering whether a product will support the growth of yeast, bacteria, or mold. (We aren’t going to discuss spores or other bacterial kingdoms here). Water content is a good measure to determine if you need to add a preservative system. Simply put, in cosmetics manufacturing, water is required to sustain and support the growth of microorganisms. No water, no microbial growth. Ipso facto, no preservation needed.

Sometimes, even if you have water, the water activity of the product can be quite low; thus, a preservative is not required. Or, the pH of a product may not facilitate organism growth, should they be present.

For your facial oil, we can operate under the assumption water activity is low due to the absence of water. Additionally, water is not going to be intentionally or inadvertently added to the product. Hopefully, it’s not going to be kept in the shower or pre-mixed with water before application. On the contrary, if this were an anhydrous hair styling paste, packaged in a jar, where a wet hand frequently dips into it, I would recommend supplementing the formula with a preservative. That’s not the case with your facial oil. If you wanted to add a preservative, there are a few out there compatible with anhydrous systems.

However, the product still needs to be preserved in the sense that shelf life needs to be conserved. Oils are inherently oxidatively unstable and could benefit from an antioxidant that prolongs stability before the oils become rancid. Therefore, the preservation is for oxygen, not microbes. Microbes can cause rancidity of oils, which in this case you may want to consider a preservative to aid in shelf stability. See, I told you it wasn’t simple!

The best way to protect oils oxidatively is to choose oils that have high intrinsic oxidative stability, source from suppliers that understand how to produce quality oils from the point of harvest, select packaging that minimizes exposure to the external environment, and supplement the formulation with an antioxidant source. BHT is an effective choice, although it’s verboten (or begrenzt?) by the clean beauty authorities. Tocopherol is a go-to selection formulators often use because it’s recognizable by consumers, but I am a rosemary extract gal myself.

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I have formulated a toner that utilizes both glycerin and butylene glycol, but it feels really slow to absorb into skin. Any advice to help improve the penetrating feel I’—TONE TIME

Dear Tone:
I personally love a sticky, over “humectant-ized” toner. After about 20 minutes of tacky phase, it eventually dries down, leaving skin feeling soft and dewy. I would venture to guess I’m in the minority. Not many want their toner to be their toner, serum and moisturizer.

I’m not sure what use levels your humectants are at, but I would definitely try reducing them substantially or reducing the glycerin—it can feel heavier than the glycols depending on what humidity you’re in. You can also try propanediol or propylene glycol in place of the butylene glycol. It tends to feel a little lighter, in my opinion.

I am focused on helping you reduce the feeling of heaviness in your toner, which may aid in the impression that it’s absorbing into skin better and not sitting topically. Perhaps you meant that you literally need to improve penetration. If that’s the case, try moving over to pentylene glycol instead of butylene glycol (keep some glycerin, but not too much). It’s a wetting agent that not only acts as a humectant but helps improve penetration of actives into skin.

If the ingredients you’re trying to penetrate are oil soluble ingredients, then you need a different strategy entirely. I would recommend DMI (an abbreviation for dimethyl isosorbide). It’—ALKALINE ALAN

Dear Alkaline:
Without knowing anything else about your formulation, I would like to wager a guess that the problem is the bentonite clay. While all clays ooze ions over time, bentonite intrinsically has a high pH value when slurried—around 9. I would switch to a clay with a lower pH, such as kaolin, which has a pH closer to the range you’re looking to target in your formulation.

While it is normal to experience some pH drift over the shelf life of a formula, this is a tad too much. In addition to switching the type of clay, consider incorporating a buffer solution into your formulation to help mitigate any pH drift. This will also be important if you’re using any other materials to help opacify the formulation, like zinc oxide or titanium dioxide, as those can contribute to a pH shift as well.

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Valerie George
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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