One of the requirements of most cosmetic products is that they have an appealing rheology. This means that you as a cosmetic formulator you are going to have to figure out a way to control the viscosity (or thickness) of your products. There are a number of ingredients that are used for this purpose. Each kind has applications to different formulation types. Here is a basic introduction.
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. They are used most often in creams and lotions. Some common types include Cetyl Alcohol, Stearyl Alcohol, Carnauba Wax, and Stearic acid.
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. Cellulose derivatives like Hydroxyethylcellulose are frequently used in liquid cleansing products such as shampoo or body wash. Guar gum is another example of a naturally derived thickener. Others include Locust Bean Gum, Xanthan Gum, and Gelatin. These thickeners can be used in any formula that contains a high level of water. Unfortunately, they can be inconsistent, cause clear formulas to become cloudy, and feel sticky on skin.
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. Materials include Silica, Bentonite, and Magnesium Aluminum Silicate. These thickeners can be used to thicken oils as well as water based formulations.
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.
I would be remiss if I 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. In a future article, we’ll discuss the salt curve and what it means for rheology.
What is your favorite cosmetic thickening agent? Leave a comment below.