Thickeners: How to select the right grade for cosmetics?

Thickeners or rheology/viscosity modifiers play a critical role in increasing the thickness (viscosity) of the formulation. In cosmetics and personal care formulations, they control texture, stability, and overall performance.

Rheology modifiers can transform formulations from thin, watery liquids into desirable forms such as creams, gels, lotions, or serums. This makes products easier to apply and more appealing to consumers.

Thickeners function by modifying the internal structure of a formulation. Depending on their chemistry, they may:

• Absorb and retain water, causing the system to swell
• Form a network or gel structure within the formulation
• Interact with other ingredients (like oils or surfactants)
• Increase resistance to flow (viscosity)

This results in improved consistency and stability.

Properties

Besides controlling flow and rheological properties, thickening agents also have other functions that aid in designing stable cosmetics. Their key features include:

• Spreadability: Enhance the spreadability of cosmetic formulations for smooth application.
• Stabilization: Prevent separation of oil and water phases (phase separation). This improves emulsion stability in creams and lotions
• Suspension: Keep particles (pigments, actives) evenly distributed in the formulation with no sedimentation at the bottom. This improves the shelf life and usability.
• Sensory enhancement: Improve feel, spreadability, and after-touch.
• Appearance improvement: Provide richness and body to formulations.

Hence, they are suitable for creams and lotions used in skin care, hair care, and sun care products.

 

Types of rheology modifiers

Natural thickeners

Natural thickeners are derived from plant-based sources and are used in clean label and sustainable formulations. They offer versatile thickening properties.

Examples include:

• Gums, such as xanthan gum and guar gum
• Cellulose derivatives such as hydroxyethyl cellulose

Synthetic thickeners

Synthetic thickeners are chemically synthesized. They are engineered to deliver precise viscosity control and high formulation stability. 

Examples include:

• Carbomer
• Other acrylate-based polymers

Associative thickeners

Associative thickeners offer multifunctional benefits by interacting with other formulation components. Thus, they help in improving suspension, stabilization, and emulsion modification. 

Examples include:

• Polymeric rheology modifiers, such as acrylates/C10-30 alkyl acrylate crosspolymer
• Hydrophobically modified polymers

Select from a wide range of commercial grades of rheology modifiers across key chemical families available in our Master Catalog for your next formulation: 
 

By choosing the right rheology modifier, you can create an effective product that is easy to use and comfortable to wear.

Now that we know the basics and types of thickening agents, let's explore common thickener incompatibility issues and their test methods to be able to formulate stable end-products.

Rheology modifiers for cosmetics must be compatible with other formulation components. This ensures optimal performance, stability, and aesthetics. Incompatibility between thickeners and ingredients such as emulsifiers, surfactants, actives, or pH systems can cause formulation defects. This can, in turn, impact the product quality and shelf life.  

Common incompatibility issues include phase separation, ingredient inactivation, and overall formulation instability. 
 

Phase separation

Phase separation refers to the separation of different phases within the formulation. It results in the formation of distinct layers or visible boundaries. It occurs when the chosen thickening agent for cosmetics is incompatible with base ingredients such as oils, emollients, solvents, surfactants, preservatives, active ingredients (like antioxidants, sunscreen agents), or pH levels of the formulation. 

Phase separation can negatively impact the:

• stability,
• appearance, and
• performance of the product

This phenomenon can manifest in different ways depending on the type of formulation and the nature of the incompatibility. In emulsion systems consisting of oil and water phases, phase separation can lead to the separation of these phases. This results in an unstable formulation. 

The rheology modifier plays a critical role in stabilizing the emulsion. It provides suitable viscosity and promotes the uniform dispersion of the oil and water phases. When the thickener is incompatible with the emulsifier or other ingredients, it can disrupt the balance between the oil and water phases. This causes them to separate.
 

Factors influencing phase separation

Impact of phase separation on product performance

• Compromised stability: Phase separation leads to an unstable formulation that is prone to separation. It changes in texture over time. The lack of stability affects the product's shelf life. It can result in inconsistent performance upon application.
• Undesirable appearance: Phase separation can cause the formulation to appear visually unappealing. The formation of distinct layers or boundaries is displeasing. This can impact consumer perception and acceptance of the product.
• Altered texture and sensory attributes: The separation of phases can result in changes in texture, consistency, and sensory attributes of the formulation. This can lead to a compromised user experience. The product may feel grainy, uneven, or unpleasant on the skin.

Ingredient inactivation

Ingredient inactivation can occur in cosmetic formulations when the chosen thickener is incompatible with other formulation components. This leads to reduced efficacy. It can alter the properties of the active ingredients. This can compromise the performance and desired benefits of the product.

 

Factors influencing ingredient inactivation
 

Impact of ingredient inactivation on product performance

• Reduced efficacy: This causes inactivation of the active ingredients. This leads to diminished product performance. The desired benefits, like moisturization, anti-aging effects, or UV protection, may not be achieved at their intended levels.
• Altered properties: Incompatibility with the thickener can alter the properties of the active ingredients. For example, changes in solubility, stability, or release profiles. Altered properties can affect the bioavailability and delivery of the active ingredient. This leads to compromised functionality.
• Decreased shelf life: Incompatibility can lead to decreased stability of the formulation over time. This can result in a shorter shelf life for the product. This is because the active ingredients may degrade or lose their potency due to incompatibility.

Compromised formulation stability

Overall instability in the formulation occurs when the chosen thickener is incompatible with other formulation components. It is a significant concern in cosmetic formulations. It can result in various issues that affect the performance, appearance, and shelf life of the product.

 

Various types of instability observed in different formulations
(F1) Congealing & creaming; (F2) Formation of lumps & Phase separation; (F3) Oil separation; (F4) Stable moisturizing cream; (F5) Stable moisturizing lotion

Factors influencing compromised stability
 

Methods to identify incompatibility issues

Compatibility testing is recommended to address phase separation, ingredient inactivation, and compromised stability. It ensures compatibility between the thickener and other formulation components. Various methods help to identify incompatibilities or potential formulation issues. These include:

• visual inspection,
• stability testing, and
• physical property analysis

Conducting these tests helps in identifying the incompatibilities early in the development process. This ensures that the thickener integrates well with other ingredients. It contributes to the desired properties and stability of the cosmetic formulation.

 

Overview of compatibility testing

Visual inspection

Visual inspection involves observing the formulation for changes. These include changes in appearance, such as color changes, phase separation, or the formation of sediments. This initial assessment can provide valuable indications of compatibility issues. Incompatibilities may manifest in various ways. For example, changes in clarity, homogeneity, or visual appearance of the formulation.

 

Stability testing

In stability testing, the formulation is subjected to various conditions. This test evaluates the physical and chemical stability. For example, temperature variations, freeze-thaw cycles, and prolonged storage periods. Stability tests can help identify any potential issues that may arise during the product's shelf life. Common stability tests include:
 

• Freeze-thaw stability: In this, the formulation is subjected to multiple cycles of freezing and thawing. This simulates temperature fluctuations. This test assesses the formulation's ability to withstand the temperature changes. The formulation must not experience phase separation, texture changes, or other stability issues.
• Accelerated stability testing: Here, the formulation is exposed to elevated temperatures and humidity conditions. This happens for an extended period, for about weeks or months, to check the stability over time. This test helps to predict the performance of the formulation under normal storage conditions.
• Long-term stability testing: Here, the formulation is stored under recommended storage conditions. This happens for an extended period, up to the intended shelf life of the product. It helps to assess the stability and compatibility of the formulation over an extended duration.

Physical property analysis

Physical property analysis involves evaluating specific characteristics of the formulation. It enables the identification of changes or issues caused by the thickener. Some common physical property analysis methods include:
 

• pH measurement: The pH of the formulation should remain within the desired range. This ensures stability and compatibility. pH changes caused by the thickener may indicate incompatibility with other ingredients. Especially if the formulation contains pH-sensitive components.
• Viscosity measurement: The viscosity of the formulation should be within the desired range. This helps to achieve the intended texture and performance. Regular viscosity measurements can help identify any changes or interactions between the thickener and other formulation components.
• Rheological analysis: It determines the flow behavior and consistency of the formulation. These tests include shear stress/shear rate analysis and yield stress determination. They can help identify any changes in rheological properties. These changes can arise due to incompatibilities between the thickener and other ingredients.

Assessing the overall performance of the formulation

It is essential to assess the impact of the thickener on the overall performance of the formulation. This includes evaluating attributes such as:

Consumer perception studies and sensory evaluations can provide feedback on the formulation's performance. It also determines the compatibility with the chosen thickener.

  

Having addressed the key incompatibility challenges and methods to detect them, the next step is to learn to select the right thickener to avoid these issues and ensure optimal formulation performance.