Consumers have always selected cosmetic products that deliver a result, while sensory stimulation was considered a secondary benefit, especially in mass market products. Today, consumer demands are growing: products must still deliver results -and do so quickly- but also amaze on many levels, even from the first use . Appealing to the senses is one way to make a lasting impression on the consumer in a short window of time. Appearance, fragrance, and texture are key elements in making an emotional connection with a consumer.
How a product feels to the touch is an important factor in the product selection. Transforming, surprising, innovative and unusual textures can make a lasting impression , but consumers assess texture even subconsciously, linking it to functionality and even value. For example, a thick lotion can be perceived as more moisturizing than a thin one.
Waxes contribute to formula functionality and sensoriality, which is why they are widely used in cosmetic and OTC drug applications. From a functional standpoint they are film formers capable of replenishing the skin’s natural lipids and contribute to water retention by the stratum corneum . As for sensory ingredients, waxes are well known for their thickening properties, but we have found they also offer a wide variety of sensations when applied to the skin. In anhydrous systems, waxes interact with oils to produce an extensive range of textures: jellies, sticks, transforming textures, creams, balms, etc. In emulsions they thicken the formula, as well as affect product esthetics such as gloss, firmness, rub-out and after-feel. In this article we will limit our focus to beeswax and its application in anhydrous formulations as a texture modifier.
Beeswax is the oldest wax known to man, with documented waterproofing uses dating as far back as 7000 BC . Beeswax has been considered a valuable resource ever since, and its use in cosmetics can be attributed to ancient Chinese people, who used it in early nail enamels.
Today, beeswax is widely used in many different areas of application, including cosmetics. In 2018, 48% of new products launched in the lip care and lip color categories with a “natural” claim contained beeswax. The persistence of beeswax usage across the globe and throughout time is due to its effectiveness and its uniqueness; including as a texture modifier.
The science behind beeswax
Waxes are water-insoluble, solid mixtures of long-chain hydrocarbons and/or esters of higher fatty acids and alcohols. They become soft, pliable, and liquid when warm and variably hard when cold . Because of this broad definition, waxes are generally classified according to their origin, allowing the chemical composition to be narrowed down within each category. Beeswax, like other natural waxes, is a complex mixture of long chain monoesters, hydrocarbons, and free fatty acids, but its uniqueness lies in the presence of polyesters, free fatty alcohols, and minor components.
Beeswax is biosynthesized by honey bees (Apis Mellifera). The process is complex, but in short, worker bees metabolize the monosaccharides found in their food sources into the lipidic components that constitute virgin beeswax . This newly secreted beeswax is then mixed with propolis – a diverse mixture of resins, oils, and pollen collected by the bee from surrounding vegetation – and chewed by the bee until it is ready for building the honey comb, with the purpose of supply storage and brood protection.
Formulation chemists will benefit from understanding both the composition of beeswax and its physical and chemical properties, as this complexity will play a role in the final formula attributes, including appearance, stability, sensory profile and performance.
Beeswax organogels and anhydrous cosmetic formulations
When beeswax is heated above its melt point and combined with a suitable solvent (vegetable oils, paraffin oils, silicone oils, etc.) and then cooled to room temperature the resulting product is called an organogel. These systems have been extensively studied in the food industry (as a replacement for trans-fats) and the technology is applicable to cosmetics as well. In fact, a good understanding of organogels can be key to a successful anhydrous formulation. In these gels, the beeswax molecules are solvated by the liquid portion of the gel; upon cooling they self-assemble into a three-dimensional network where the liquid is entrapped within. These networks are thermo-reversible and have viscoelastic properties . Many waxes thicken and structure oils in this manner and the gel hardness is always proportional to the percentage of wax. However, the rest of the textural properties are not so easily predicted, as they depend on a balance between the solubility (and insolubility!) of the oils and the waxes. Furthermore, the manner in which the gel is cooled will also have an impact on texture: gels that cool undisturbed will be harder than gels that cool with mixing.
Figure 1 shows the hardness of beeswax gels (measured by ¼ cone penetration) at three different concentrations and in three different oil mediums. In general, as the percentage of beeswax increases, so does the gel strength (lower penetration values). Also in general, beeswax yields harder gels in more polar oils (castor oil) and softer gels in less polar oils (isopropyl palmitate).