Rheology modifiers in cosmetics often referred to as thickeners or viscosity modifiers, do much more than just alter the thickness of a product. They play a key role in enhancing the overall performance and skin feel of cosmetic or personal care products, influencing factors like flow, stability, and spreadability.
Benefits of rheology modifiers:
- Textures: Serum, gel-jelly, cream, balm, gel-cream, oil, spray, lotion.
- Skin feel/sensory attributes: Spreadability, greasiness, tackiness, fluidity, absorption, coding effect, etc.
- Stability and shelf life of products: Suspension control, reduce phase separation, prevent syneresis.
Whether it’s for skin care or makeup, understanding the function, types, and application of these additives is essential in crafting the perfect formulation to address the consumer need.
Not all rheology modifiers behave the same way. Their performance depends on aspects such as:
- the type of formulation in which they are incorporated,
- the working pH range,
- compatibility with other ingredients,
- processing and shear conditions,
- the desired texture and stability profile.
Understanding these characteristics makes it possible to select suitable rheology modifiers for each cosmetic application and avoiding unnecessary adjustments.
There are four key measurements that provide accurate and predictable information for developers to better understand outcomes of rheology modifiers. They include:
- Viscosity: The material’s resistance to movement, or “thickness.” Water has a low viscosity and high flow. Honey has a high viscosity and low flow.
- Yield stress: The transition between solid-like and fluid-like behaviors. Shaving cream at rest has a high viscosity but becomes more liquid-like when stress is applied (like when you rub it on skin or wash it with water).
- High shear viscosity: The material’s thickness under a force applied parallel to its surface. Soap that’s designed to foam as it exits a pump changes its viscosity under a high shear rate.
- Zero-shear viscosity: The material’s thickness at rest. If this is too low, different ingredients in a formula might begin to separate, causing sedimentation.
Among rheology modifiers there are mainly 4 categories depending on their origin:
Natural origin: the rheology modifier comes from a plant or a specific part of the plant (root, seed, fruit, etc) and its percentage of naturality has been calculated according to ISO 16128. For example, it is the case of glucomannan,
Modified natural origin: the rheology modifier is extracted from nature but has been through a chemical process and it modifies its properties such as a common example, derivatives from cellulose.
Synthetic origin: rheology modifiers from petroleum based such as polyacrylamide, acrylates copolymers, etc. For instance, Polyacrylate Crosspolymer-6
Inorganic origin: rheology modifiers come from inorganic resources such as clays, silica…
