Cosmetic thickeners and stabilizers
Thickeners are considered an aesthetic modifier (as discussed more in this post about types of cosmetic ingredients). In a formula they are essential for creating a product that is appealing to your consumer. While function (ie moisturizing, cleansing) is paramount, how a product feels can be almost as important to the end user and set your product apart from the competition.
Reasons for using thickeners:
- As the name suggests, thickeners (sometimes referred to as rheological additives) are used to build viscosity and deliver optimal product consistency to your consumer.
- They are also used to suspend additives in your formula
- And improve product stability
Choosing a Cosmetic Thickener
Here are the factors to consider when choosing a thickener.
- Formula type
- Packaging
- Viscosity and rheology
- Consumer use
- Manufacturing conditions
Let’s dig into this list a little deeper…
What type of formula are you making?
While it’s fairly intuitive that thickeners build viscosity in water and oil based products, you may be surprised to learn that thickeners are also used in waxes and solid formulations. Thickeners can provide stability in emulsions and foams and suspend solid particulates. In other words, it may not always be obvious that you need a thickener or stabilizer so understanding the basic chemistry is important in creating a stable and consumer desirable product.
Also, while a product may have optimal consistency in a small beaker in a lab, you could see different results as you scale-up your formula for full production. We’ll discuss this in more detail later in the post when we review the different types of thickeners and the products they are best suited for.
How does packaging impact your product?
Product packaging can actually have a big impact on viscosity. The act of pumping a product out of a bottle or squeezing it out of a tube can alter the rheology and negatively impact the consumer experience. It’s critical that you perform stability testing and consumer testing (if applicable) in the actual packaging that it will be sold in to make sure you’re not compromising product aesthetics.
Why are viscosity and rheology important?
These aren’t terms you use every day (I had to bust out some chemistry books here myself!) but viscosity and rheology are both important terms to understand in your path to identifying the best thickener for your formula. While viscosity indicates the thickness of your formula (or resistance to flow), rheology speaks to the flowability of your formula - in other words, how viscosity is impacted by different conditions (like shear).
Newtonian liquids like water and oils produce straight lines in both the flow and viscosity curves (viscosity and shear are proportional). However, cosmetic emulsions often exhibit non-Newtonian properties, meaning these materials exhibit different flow characteristics depending on shear rates. As mentioned previously, this is really important to take into account when scaling up formulas for production as shear rates are vastly different in beakers vs manufacturing drums.
What’s the intended consumer use?
When formulating, you want to ensure that your product matches the marketing promise. For example, the expectation of a thick body butter compared to a light cream are different and you should adjust your rheology accordingly.
What are your manufacturing conditions?
This will be mentioned throughout this post, but it is critical you are able to replicate product specifications from the lab into actual manufacturing conditions. While many large companies have process engineers that work specifically to scale up products, you’ll want to be aware of the manufacturing conditions and make sure you are aligned on product specifications throughout the development process.
Types of cosmetic thickeners
There are 5 main types of thickening agents used in formulations. These include
- Lipid thickeners
- Naturally derived thickeners
- Mineral thickeners
- Synthetic thickeners
- Ionic thickeners
Lipid Thickeners
Lipid thickeners are primarily composed of lipophillic materials. They work by imparting their natural thickness to the formula. Typically, these materials are solids at room temperature but are liquified via heat and incorporated into emulsions. While they are primarily used to build viscosity they can also be used to to improve film thickness and improve water resistance.
Examples:
- Waxes (ie bees, candelilla, camauba) - used primarily in stick formats like lipsticks.
- Cetearyl alcohol, cetyl alcohol, myristyl alcohol, stearyl alcohol - used to improve consistency/skin feel and stabilize emulsions (usually as a co-emulsifier).
- Hydrogenated castor oil, hydrogenated palm glycerides, hydrogenated peanut oil, hydrogenated tallow glycerides - used as consistency agents.
Naturally derived thickeners
Various thickeners are found in nature or are derivatives of natural thickeners. These ingredients are polymers that work by absorbing water to swell up and increase viscosity. These thickeners can be used in any formula that contains a high level of water. Unfortunately, due to their natural origin they can be inconsistent which can cause variability in performance, odor and color. They also can be incompatible with other ingredients in your formula, can cause clear formulas to become cloudy, and feel sticky on skin. While natural thickening agents are popular choices in the “clean” beauty era they often require trial and error and aren’t the best choice for all formulas.
Examples:
- Cellulose (ie cellulose gum, hydroxyethylcellulose, methyl cellulose)
- Starch/starch derivatives (ie aluminium starch octenylsuccinate, sodium polyacrylate starch)
- Gums, etc (ie guar gum, xanthan gum, carrageenan, pectins, agar)
Mineral thickeners
Mineral thickeners are naturally occurring, mined ingredients that can absorb water or oils and boost viscosity. They give a different kind of viscosity than the natural gums. These thickeners can be used to thicken oils as well as water based formulations (and sometimes powders).
Examples:
- Silica
- Bentonite
- Aluminium-stearate
- Zinc stearate
Synthetic thickeners
Perhaps the most versatile of all thickeners are the synthetic molecules. Carbomer is the most common example. It is a water-swellable acrylic acid polymer that can be used to form crystal clear gels. They have a desirable feel which makes them superior to other thickening agents that leave a sticky feel. Carbomer thickeners also have the ability to suspend materials in solution so you can have low viscosity formulas with large particles suspended. These thickeners also help to stabilize emulsions and are frequently used in lotion and cream products. Acrylates also produce a thickening effect. PEG (polyethylene glycol) thickeners are also important in emulsions.
Ionic thickening
We would be remiss if we didn’t mention one of the most common thickeners for surfactant solutions. Simply adding Salt (NaCl) you can get an anionic surfactant solution to become thicker. In fact, salt is frequently used as an adjusting agent during production.
Using thickeners in emulsions
Even with the use of an emulsifier, emulsions will eventually break down over time. Using a thickener to increase viscosity and stabilize the emulsion will help maintain the integrity of your formula in the long-term. Hydrocolloid thickeners like Carbomer or Xanthan gum are usually used in O/W emulsions to provide stability. In order to regulate consistency, hydrophilic ingredients like cetyl or cetearyl alcohol are good choices.
Example of hair gel formula using Carbomer:
- DI Water > 90%
- Polymers such as PVP/VA Copolymers, Polyquaternium-11, etc - these provide fixative/hold properties
- Carbomer - creates a gel like texture (thickening agent)
- Neutralizing agent such as TEA, AMP, etc - used to neutralize the Carbomer to improve “swelling”
- Humectant/solvent like propylene glycol - improves clarity and solubilizes preservative system
- Water-soluble UV filters - prevents color degradation
- Chelating agent such as EDTA disodium salt - stabilizes formula and helps preservative work better
- Preservative - prevents mold/bacteria from growing
- Fragrance
For W/O emulsions, waxes or mineral thickeners are typically used to improve stability, maintain viscosity and improve flow.
Conclusion
The role of thickeners and stabilizers in cosmetics goes well beyond just building viscosity. Formula type, consumer preferences and marketing positioning all play a role in determining what thickener is best suited for your product and some trial and error is usually needed to get the best result. You may find that you need to use a few different rheological additives in order to get the optimal texture, stability and quality of your formula.
References:
Handbook of Cosmetic Science and Technology. Marcel Dekker, Inc., New York, NY, 2001. Chapter
A Short Handbook of Cosmetology. K.F. De Polo 1998, Printed in Germany. Chapter 6 and 8.
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