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Editor's note: This excerpt* from the May 2012 issue of Cosmetics & Toiletries reviews some of the components in hair styling products. The full article additionally includes methods to test hair styling products for efficacy.
Inherent hair factors including variations in the morphology and mechanical properties of hair impact styling. For instance, thicker hair is more difficult to style and the style is more difficult to retain. Cuticle edges are another factor; hair with less frequent cuticle edge intervals is more flexible and easier to bend and manipulate, which has a significant influence on the durability of a hair style. Hair shape itself also influences the ease of styling, with spherical-shaped hair being more difficult to style than elliptical shaped hair. While these characteristics are important considerations, the cosmetic chemist obviously can only control external factors such as the features of products or functional ingredients applied to hair.
Styling products take on a myriad of forms. One level of differentiation is whether they are applied to hair as a thickened liquid or a spray. With aerosols, the product is atomized either mechanically using specialized pumps or with pressurized liquefied propellant gases such as propane. Other products include clear to translucent gels, cream gels, low viscosity lotions, pomades, taffies, stringing pomades, light-airy soufflés and clays and waxes.
In some cases, there is an overlap between aerosol technology and products that do not require atomization. For example, aerosol mousses rely on a propellant as part of the delivery mechanism to produce foam. There are also foam mousses produced mechanically using a special actuator. Spray gels require mechanical breakup as non-aerosols but the product form in the container is a gel.
The main type of ingredient added to styling product vehicles is the fixative resin. Here, usually a high molecular weight and water-soluble polymer dries into a resinous film that imparts the desired mechanical properties of stiffness and elasticity to the hair fibers or fiber assemblies. The chemistry of these polymers has evolved over the past 50–60 years and new monomer combinations with various functional groups have increased the features and benefits these polymers provide.
The film qualities of a resin can be modified with auxiliary ingredients such as plasticizers. The addition of a polyhydric alcohol such as glycerin or an ethoxylated nonionic surfactant or emollient such as PEG 75 lanolin will tend to soften the film on the hair. This is due to the disruption of the interactive forces of the polymer molecules in the resinous film, increasing film pliability. The result is reduced flaking during combing, a problem with some homopolymers such as PVP, and improved smoothness properties.
The negatives, however, may be a compromise of other fixative properties, such as hold under humid conditions and reduced stiffness. This is the case with most cream gels that have a certain amount of oil, whether it is organic, petroleum- or silicone-based, dispersed in the gellant. These gels compromise fixative properties for other benefits such as anti-frizz effects, which require the addition of silicone. Examples of commonly used silicones include low and high molecular weight dimethicone and dimethiconol, and phenyltrimethicone. A typical cream gel designed for normal and undamaged hair contains a small oil phase so that the oil does not weigh the hair down and negatively affect hair volume and body, while providing enough oil to enhance hair shine, condition and styling.
The level and type of neutralizing agent for fixative polymers that require neutralization, e.g., those with a carboxylate group, will tend to affect film properties as well. Organic amines such as aminomethylpropanol (AMP) and triethanolamine (TEA) will have more of a plasticizing effect than an inorganic alkali such as NaOH. Organic amines may reduce film hardness and, in some cases, high humidity curl retention. Besides the fixative, fixative modifying and gelling ingredients, other components may include preservatives, chelating agents, UV absorbers, fragrance and fragrance solubilizers, feel modifiers and color.
* Adapted from T Evans and RR Wickett, Advances in hair styling, in Practical Modern Hair Science, Allured Business Media: Carol Stream, IL USA (2012)
This is only an excerpt of the full article that appeared in Cosmetics & Toiletries, but you can purchase the full-text version.