Hot or Not

Dear Valerie: When do I add Vitamin E to water-in-oil emulsions? At first, I thought that Vitamin E was heat-sensitive. After reviewing the literature, I see it is not as heat sensitive as I thought. Some food studies show really high temperatures for degradation. Can I add it hot? 

—Heat Miser

Dear Heat:

As an antioxidant, tocopherol is swept into this general category of delicate raw materials that shouldn’t be exposed to any heat. However, this unctuous, dark oil is difficult to effectively incorporate into emulsions at low temperatures. For some emulsion systems, it’s not even possible to add tocopherol upon cool down. 

You’re right—there is an abundance of literature that evaluates thermal degradation of tocopherol, and the studies show the heat requirement for its decomposition is quite high. It’s important to consider that most of the studies don’t look at tocopherol in isolation, but rather as a natural part of oil content that is then exposed to high heat.^1,2 The oils contain different fatty acids that have the potential to protect tocopherol from degradation. Therefore, I don’t believe their findings wouldn’t necessarily extrapolate to crude tocopherol. 

I do believe that tocopherol probably has some capacity for heat. However, there are two aspects I raise for consideration. When working on a lab scale, the heat contact time tocopherol has is quite minimal. If you’re only making emulsions in the lab, or you’re producing only very small batches efficiently, you’re likely not exposing the product long enough to heat to be overly concerned about the tocopherol degradation.

Manufacturing is a completely different story. An emulsion on any meaningful production scale is exposed to heat for hours. Should something go wrong on the machinery side, that time can really be extended. We once had a product that required warm filling. It took 36 hours due to some filling issues. Any tocopherol present would have been zapped.

It’s also not always super easy to fine tune control temperatures on manufacturing kettles; often there are ranges of heat allowed. Sometimes the equipment gets a little too hot. I imagine this is all not an ideal scenario for tocopherol, or representative of the couple hours you spent in the lab heating it up.

Heat is only one catalyst of tocopherol decomposition. Exposure to oxygen is another. Of course, your tocopherol may degrade on-shelf, where it’s exposed to oxygen in the ambient atmosphere. How much?  I’m not sure as I’m not aware of any studies measuring tocopherol stability over time in a cosmetic formulation, relative to heat exposure during processing, versus a control. But it’s safe to assume it happens. I guess there is no clear answer but just use caution and you should be fine.

Now I’m wondering why you’re adding tocopherol to an emulsion. If your objective is to protect the oil phase of the formulation, that’s probably okay, but you could also consider supercritical CO2 rosemary extract with a high (and standardized) carnosic acid content). Or BHT if you are allowed to use it. Additionally, consider employing the food studies you have read, selecting oils high in tocopherol. This is not a common reporting measurement, however, so you may have to accept generalities. I once did extensive research on tocopherol content of different kernel oils. It’s expensive; perhaps relying on the manufacturer statements is better.

If your goal is to protect the aqueous phase, there are more effective antioxidants such as cinnamic acids (use care when incorporating as they’re sparingly soluble), or the real good stuff, sodium sulfite.

If your goal is to deliver antioxidant protection to the skin, you have many more choices that can be added when the product has cooled. You could also consider tocopheryl acetate. As an ester, it’s extremely thermostable compared to the alcohol. It does have significantly poorer penetration than tocopherol and must be enzymatically concerted to the active form, but at least you would be guaranteed to have some tocopherol (even if minute) in the skin!

References

1. Kuppithayanant, N., et al. “The Effect of Heating on Vitamin E Decomposition in Edible Palm Oil.” International Journal of Environmental and Rural Development, vol. 5, no. 2, 2014, pp. 121-125. J-STAGE, 31 Mar. 2021.
2. Bayram, Ipek, et al. “Mathematical Modeling of Alpha-Tocopherol Early Degradation Kinetics to Predict the Shelf-Life of Bulk Oils.” Journal of Agricultural and Food Chemistry, vol. 72, no. 9, 2024, pp. 4939-4946. American Chemical Society, doi:10.1021/acs.jafc.3c08272.

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