COSMETICS AND BATHROOM PRODUCTS:HAIR CONDITIONERS.

HAIR CONDITIONERS

The natural condition of the hair depends on the physical state of the outer protective sheath of the hair shaft (called the cuticle). The cuticle consists of dead cells arranged as stacked transparent plates that reflect light. Factors such as general environmental and chemical exposure, excess heat, and/or excessive mechanical styling dislodge and fray the tile cells, thereby allowing the hair shaft to be exposed to dehydration by progressive cuticle deterioration. The cortex becomes susceptible to damage, especially in the area close to the fiber tips. In addition, the hair takes on a dull appearance as the hair in general has reduced reflective capacity, and the raised tile plates cause the hair to be more susceptible to tangling. Conditioners help keep hair from tangling by leaving a waxy coating on the hair shaft, thereby smoothing the cuticle tile plate cells down in place. Conditioners in general contain active materials that are adsorbed or absorbed onto the hair surface, thereby changing the surface energy and friction, providing gloss, shine, enhanced tactile properties, manage- ability, and body to otherwise potentially dry, brittle, damaged, and dull (non-light-reflective) hair. Different types of conditioners include condi- tioners and cream rinses (to be applied after shampoo and rinsed off shortly thereafter), leave-in conditioners (designed to be left on hair after application with no rinsing), and deep conditioners (to provide intensive treatment; designed to be left on hair between five and twenty minutes and then rinsed off). Generally, conditioner ingredients include water, primary conditioning agents (quaternary ammonium salts, cationic poly- mers, silicones), refatting agents (fatty alcohols, waxes), secondary con- ditioning agents (natural oils, silicones), emulsifier (typically nonionic surfactants), specialty additives (proteins, resins, dyes), thickeners, pH adjusters, fragrance, and preservatives.

Hair consists mainly of the protein keratin, and in general, the sorp- tion of a cosmetic ingredient onto hair is governed by its attraction or binding with the negatively charged composition of keratin amino acids. Other structural elements, such as lipids, may also contribute to the dy- namics of colloidal structure adsorption onto hair. Modern conditioning products are the result of the development of mild detergents and cat- ionic surfactants in the 1940s and 1950s. Modern conditioners consist mainly of long-chain alcohols or long-chain quaternary ammonium salts that coat hair fibers. Cationic surfactants such as quaternary ammonium compounds (e.g., cetrimonium chloride, stearalkonium chloride, quater- nium-18, -27, and -80) are the salts of strong acid or strong base and contain a hydrophilic cationic group (attaches to keratin) carrying one or two hydrophobic hydrocarbon chains (provides conditioning). In addi- tion, cationic polymers (e.g., acrylates copolymer, guar hydroxypropyl- trimonium chloride, polyquaternium-4, -24, -11, -28, -6, -7, -39, -16, and -2) may be used as conditioning agents, as they also display high af- finity for negatively charged keratin.

First introduced in the 1970s, many hair conditioners now contain silicone-based lubricants as their primary conditioning agents. Linear long- chain silicone copolymers applied to wet hair allow for quickened hair dry- ing by their displacement of water molecules. They may also improve hair luster, help the appearance and texture of damaged hair, and reduce hair fric- tion and static, thereby preventing a situation known as “fly-away hair.” Enhanced ability to decrease hair static may be achieved by the addition of functional groups such as amines to the silicone molecules. Silicones com- monly used include dimethicones, dimethicone copolyols, cyclomethicones, phenyl trimethicone, amodimethicones, and trimethylsilylamodimethicones.

Proteins and their hydrolysates are another class of conditioning agents; these include materials derived from animals and vegetables, such as keratin, collagen, elastin, silk, soy, corn, and wheat. They can be used to protect and repair damaged hair, including the temporary mending of “split ends.” Additional ingredients of conditioners include fatty compounds that

provide hair lubrication and luster and act as thickeners, emulsion stabi- lizers and/or emollients (e.g., oleic acid, stearic acid, linoleic acid, lauryl alcohol, cetyl alcohol, stearyl alcohol, glycol stearate, polysorbate 20, beeswax, lanolin, glycerin, mineral oil, almond oil, and avocado oil). Sol- vents (e.g., water), pH adjusters (e.g., lactic acid, citric acid), botanical ingredients (e.g., rosemary, sage, ginseng), vitamins (e.g., B, A, E, pan- thenol, extract of wheat germ), UV absorbers (e.g., benzophenone-4), preservatives (e.g., parabens, disodium EDTA, diazolidinyl urea), color, and fragrance are also often added to provide product substance, ensure product chemical reactivity, enhance antioxidant properties, strengthen hair roots, stimulate natural growth, stimulate keratinization, protect against damaging sun-based UV radiation, ensure product antimicrobial purity, and enhance product quality.