Testing the Stability of Solid Cosmetics

Solid cosmetics are a beauty industry staple, with soaps and lipsticks common examples. Recently, their use has been accelerating within the cosmetics industry. These cosmetics offer some distinct advantages over liquid formulations for certain applications.

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The benefits of solid cosmetics include convenience, higher concentrations, and compatibility with low-waste, plastic-free, and fully recyclable packaging. To meet the increasing ecological awareness of consumers, cosmetics manufacturers are rolling out new solid formulations for a wide range of products.

Solid formulations have been developed for products such as shampoos, make-up, deodorants, perfumes, and even toothpaste.1 This article will discuss this emerging class of cosmetics products and Formulaction’s solution for rapid stability testing.

The Importance of Stability Testing for Solid Cosmetics

Stability is a primary concern when developing solid cosmetics. For instance, lipsticks that fade or solid perfumes that smell worse over time are undesirable products.2

Unstable personal care products can deteriorate on the shelf in several ways. For example, in wax- or oil-based solid cosmetics such as lipstick, the two most common problems are the exudation of oil droplets and the formation of crystals of waxy compounds on the surface.

Product instabilities can lead to critical issues. Cosmetics must fulfill the same function every time and possess the same qualities after extended use. If they rapidly deteriorate, consumers can find them unappealing and unusable.

To overcome these issues, new products must be rigorously tested, with their stability and shelf-life thoroughly evaluated before they can be brought to the market.

Researchers traditionally evaluate products by exposing them to worst-case scenarios which may be encountered in the real world. For example, products are left on shelves for prolonged periods of time and exposed to direct sunlight and temperature fluctuations.

Common stability testing procedures include heating products such as lipsticks to 40 °C over 12 hours, then cooling them to 4 °C over the next 12 hours, and repeating this cycle for between 1 and 6 months before the product is sold.

The journey of a new cosmetic product from initial research and development to quality testing and final approval is lengthy. While essential for ensuring the final quality of a solid cosmetic product, stability testing over weeks and months can present a serious bottleneck for manufacturers.

The longer a product undergoes stability testing, the greater the chance of the manufacturer losing a critical market advantage. On the other hand, ending stability testing prematurely runs the unacceptable risk of mass-producing and selling an unstable product.

Accelerating Stability Testing

It is commonly assumed that stability testing of solid cosmetics can only be achieved by imitating the conditions under which they might deteriorate, including thermally cycling them over relatively long periods.

Using the right technology can, however, dramatically accelerate the process. Utilizing innovative stability testing methods allows manufacturers to accurately anticipate the long-term behavior of solid cosmetics.

This is where the Rheolaser Crystal from Formulaction – a unique microstructural thermal analyzer that enables accurate long-term stability analysis in a matter of hours – comes into play.

The Rheolaser Crystal relies on the Diffusing Wave Spectroscopy (DWS) principle. Observing the scattering pattern produced when a laser is incident on the surface of a sample enables the device to monitor nanometer-size variations in structure.

Minute structural changes can significantly impact the sample’s scattering pattern. Formulaction’s analyzer can accurately characterize these structural changes in the sample in terms of a characteristic timescale τ.

The Rheolaser Crystal combines DWS capabilities with a precise temperature control unit that enables thermal cycling of the sample, typically between 4 °C and 40 °C.

Stable formulations respond to thermal cycling with an equal signal across multiple temperature cycles, while unstable formulations show an easily detectable signal variation.

Unlike conventional solid cosmetic stability testing, the Rheolaser Crystal enables measurements to be obtained in a matter of hours rather than months. Samples can be quickly ranked in order of stability.

Due to the sufficiently large size of samples, the method is robust, easily handling inhomogeneities in cosmetics samples. The Rheolaser Crystal is engineered with usability in mind and analysis can be launched in a single click.

Any solid or semi-solid sample can be analyzed in the system’s adaptable sample holders. The analyzer works with samples as big as 5 g and as small as 0.05 g, and provides temperature control from 4 °C to 90 °C.

The Rheolaser Crystal removes the quality control bottleneck for solid cosmetics, enabling manufacturers to accelerate their products’ journey to market.

The system’s sensitivity and precise temperature control make it the fastest and most accurate solution for monitoring microstructure evolution in solid cosmetics, ensuring the quality of the manufacturer’s products.

Contact the Experts

Formulaction is changing the way manufacturers and researchers analyze the end-use properties of products. To find out more about the Rheolaser Crystal or to book a free demo, contact a member of the Formulaction team today.

References and Further Reading

  1. Solid Cosmetics : A “solid” future in the beauty industry? | Safic-Alcan : Specialty Chemicals Distributor | Innovative Formulations. https://www.safic-alcan.com/en/us/solid-cosmetics-solid-future-beauty-industry
  2. Barel, A. O., Paye, M. & Maibach, H. I. Handbook of Cosmetic Science and Technology | Stability Testing of Cosmetic Products. (CRC Press, 2009).

This information has been sourced, reviewed and adapted from materials provided by Formulaction.

For more information on this source, please visit Formulaction.

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