How We Solved the Problem of Emulsion Instability in Professional Salon Shampoos: A Practical Case from Cosmetic Production

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Producing professional shampoos for hair salons demands high emulsion stability. One of our clients faced repeated phase separation after several weeks of storage, despite the original formulation passing standard tests. The issue was particularly evident during temperature fluctuations during transport or storage in non-air-conditioned spaces. Analysis revealed that the key factor was not only the choice of emulsifier but also the interaction between surfactants, thickeners, and preservative systems. How did we approach the solution, and which mistakes should be avoided?

Problem: Unstable emulsion and its impact on production

In cosmetic production, the stability of emulsions is one of the fundamental quality parameters that determine a product's success on the market. In our case, it involved a professional shampoo designed for hairdressing salons, where instability manifested as phase separation after just a few weeks of storage. The problem was not apparent immediately after production but only after transport and temperature fluctuations, which complicated complaints and logistics. The oil-in-water (O/W) emulsion contained a combination of anionic and non-ionic surfactants, silicones, and thickeners, with the interaction of these components gradually disrupting homogeneity.

Instability manifested in several ways: the creamy consistency became more fluid, an oily layer formed on the surface, and flocculation occurred in some batches. This not only reduced the product's aesthetic value but could also affect its efficacy—for example, uneven distribution of active ingredients or silicones. For professional salons, where shampoo consistency and performance are crucial, this problem posed a risk of losing customer trust and increased quality control costs.

Cause Analysis: Where Did the Mistake Occur?

The first step toward a solution was detailed laboratory testing of the problematic batches. Using standard test methods, we verified viscosity, pH, particle size, and the microscopic structure of the emulsion. We found that the key factor was insufficient compatibility between emulsifiers and thickeners. Specifically, the combination of carbomer and a non-ionic emulsifier based on ethoxylated fatty alcohols did not provide adequate stability at temperatures above 40 °C, which corresponded to conditions during summer transport.

Another issue was the uneven dispersion of silicones, which tend to migrate to the surface of the emulsion. This was caused by the excessively low viscosity of the continuous phase and insufficient network structure of the thickeners. The analysis also revealed that some raw materials had a higher impurity content than declared, which could have contributed to destabilization. Based on these findings, we focused on optimizing the formulation with an emphasis on selecting compatible emulsifiers and stabilization systems.

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Solution: Formulation and Production Process Optimization

Based on the analysis, we adjusted the formulation in three main areas. First, we replaced the original emulsifier combination with a system based on anionic and nonionic surfactants with a higher hydrophilic-lipophilic balance (HLB), which better stabilizes the oil phase. Second, we added a secondary phospholipid-based emulsifier, which improved the emulsion's network structure and limited silicone migration. The third key change was replacing carbomer with a xanthan gum-based thickener, which is less sensitive to temperature fluctuations and provides more stable viscosity.

In addition to adjusting the formulation, we also optimized the production process. We increased the homogenization temperature to 70–75 °C to achieve better dispersion of the oil phase and extended the mixing time after adding thickeners. An important step was also the introduction of gradual emulsion cooling, which prevented sudden viscosity changes. These changes led to a significant improvement in stability – the tested batches remained homogeneous even after 3 months of storage at temperatures ranging from 5 to 45 °C.

Results and Practical Recommendations

After implementing the changes, we conducted a series of accelerated stability tests according to standard protocols, including temperature cycling (5–40 °C) and centrifugation. The results confirmed that the modified formulation meets stability requirements even under extreme conditions. Additionally, the product exhibited improved foaming and washability, which was also appreciated by end users in salons. An important finding was that even small changes in emulsifier concentration or the type of thickeners can have a significant impact on long-term stability.

For cosmetic manufacturers, we recommend paying increased attention to raw material compatibility already during the formulation development phase and conducting stability tests not only under standard conditions but also by simulating real transport and storage temperatures. Additionally, it is advisable to invest in microscopic analysis of emulsions, which can reveal potential issues with particle size or flocculation. Last but not least, collaboration with raw material suppliers is crucial, as they can provide technical support and certified materials with consistent quality.

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Impact of Emulsifier Selection on Emulsion Stability: Key Factors

The stability of emulsions in cosmetic products such as shampoos primarily depends on the correct selection and combination of emulsifiers. Emulsifiers reduce the surface tension between the aqueous and oil phases, enabling the formation of a homogeneous mixture. In practice, anionic, nonionic, or amphoteric surfactants are often used, each type having specific properties. For example, anionic emulsifiers, such as alkyl sulfates, provide strong cleansing effects but may be aggressive to the skin. Conversely, nonionic emulsifiers, such as ethoxylated fatty alcohols, are milder and better tolerated but require precise dosing and combination with other ingredients to achieve the desired stability.

Another important factor is the hydrophilic-lipophilic balance (HLB) of emulsifiers. The HLB value determines whether the emulsifier will better stabilize oil in water (O/W) or water in oil (W/O). For shampoos, emulsifiers with a higher HLB value (8–18) are typically used, as they support the formation of O/W emulsions. Incorrect selection of the emulsifier or insufficient quantity may lead to phase separation, clumping, or changes in viscosity. In our case, we found that the original formulation contained an emulsifier with too low an HLB value, resulting in instability during storage and temperature fluctuations.

The Role of pH and Viscosity in the Long-Term Stability of Shampoos

pH value and viscosity are additional critical parameters that influence emulsion stability. Shampoos for professional salons must have a pH in the range of 4.5–6.5 to be gentle on hair and the scalp. At higher pH levels, hydrolysis of certain ingredients, such as silicones or preservatives, may occur, leading to emulsion degradation. Conversely, excessively low pH may cause corrosive effects on packaging materials or skin irritation. In our case, we found that the original formulation had a pH at the upper limit of the recommended range, which accelerated emulsion breakdown during storage.

The viscosity of shampoo is also crucial for its stability and user comfort. Too low a viscosity can lead to rapid phase separation, while too high a viscosity makes application difficult and may mask stability issues. To adjust viscosity, thickeners such as salts (e.g., sodium chloride) or polymers (e.g., carbomers) are often used. In our solution, we optimized the amount of thickeners and simultaneously adjusted the pH using citric acid, thereby achieving a more stable emulsion and consistent texture throughout the shelf life.

Stability Testing: Methods and Their Importance for Production

Various tests are used to verify the stability of emulsions, simulating real storage and usage conditions. The most common include stability tests at different temperatures (e.g., 4 °C, 25 °C, and 40 °C), temperature cycling (alternating cold and heat), and centrifugation. These tests help identify potential issues such as phase separation, color changes, or odor development before the product is launched on the market. In our case, we conducted extensive testing, which included storing samples at 40 °C for 3 months and temperature cycling between 4 °C and 40 °C for 14 days.

Another important method is microscopic analysis, which allows for the visual assessment of the size and distribution of emulsion droplets. An ideal emulsion should have uniformly distributed droplets with a diameter of 1–10 micrometers. In the case of our original formulation, we observed uneven droplet distribution and their gradual coalescence, leading to phase separation. After optimizing the formulation and production process, we achieved a homogeneous emulsion with uniform droplet distribution, which was confirmed by repeated stability tests and microscopic analysis.

Need a Custom Stable Formulation?

Every cosmetic raw material from GCG Group is supplied with a detailed technical data sheet and safety data sheet (SDS), which includes recommendations for storage, mixing, and stability. Our experts will assist you in selecting suitable components and optimizing the formulation for your specific needs. Contact us – or browse our catalog of over 1,300 products right away.