Shampoo & hair conditioners

Shampoos
Shampoo is a basic hair care product representing the largest segment of hair care cosmetics. Shampoo is typically in the form of a viscous liquid with some exception of waterless solid form such as a bar. Shampoo was developed to replace soap for cleansing scalp and hair by removing unwanted sebum, dandruff, environmental dust, and residues of hair care products. Most of the dirt including sebum are water insoluble and cannot be effectively removed by water alone. Therefore, a shampoo containing a combination of surfactants is necessary. The content of surfactants in a shampoo is typically between 10% and 20%. An example of cleansing shampoo formula is given in Table 36.2.

Table 36.2. An Example of Conditioning Shampoo Formula

Ingredient Function % (w/w)
Sodium laureth sulfate Primary surfactant for lathering and cleansing 16.0
Cocamidopropyl betaine Cosurfactant for lathering 2.0
Cocamide MEA Cosurfactant for lathering 2.0
Glycol distearate Pearling agent 1.5
Dimethicone Conditioning agent for dry hair 1.0
Guar hydroxypropyltrimonium chloride Conditioning agent for wet hair 0.5
Citric acid pH adjuster qs
Sodium chloride Viscosity booster qs
Preservatives Preservation qs
Perfume Fragrance qs
Deionized water Solvent qs to 100
Surfactants emulsify oily dirt on hair and scalp, then the dirt can be pulled into water and washed off easily (Fig. 36.1).8 The cleansing effect of a shampoo can be observed by comparing the scalp image under a microscope before and after using shampoo (Fig. 36.2).6 After shampooing, scalp becomes clean and free of the oily dirt until fresh sebum is regenerated. This action helps maintain personal hygiene and reduce the chance of scalp inflammation, itching, and odor.

A class of surfactants called anionic surfactants such as sodium laureth sulfate, ammonium laureth sulfate, sodium lauryl sulfate, and ammonium lauryl sulfate are the primary cleansing agents in shampoo. Amphoteric types of surfactants such as cocamidopropyl betaine and nonionic surfactants such as cocamide MEA are also often used as cosurfactants in shampoo to stabilize micelles formed, helping improve lather stability and viscosity building.

In addition to shampoo’s primary cleansing function, antidandruff shampoos and conditioning shampoos also became popular decades ago.

Dandruff is a common scalp disorder often accompanied by scalp itching.9 It is known that dandruff is associated with a scalp-specific fungus named Malassezia.10–13 Malassezia metabolizes triglycerides in sebum by the expression of lipase, resulting in an unsaturated lipid byproduct. The unsaturated lipid penetrates into top layer of the epidermis, resulting in an inflammatory reaction. Dandruff is considered a result of the inflammatory reaction.

Not only can it wash off dandruff on scalp as ordinary shampoos do, an antidandruff shampoo usually contains antifungal actives for inhibition of Malassezia. Well-known antifungal actives include zinc pyrithione, piroctone olamine also known as octopirox, selenium sulfide, climbazole, ketoconazole, and ciclopirox. Sulfur, salicylic acid, and coal tar are also used sometimes, though they are relatively low in antifungal activity. Among these, zinc pyrithione and octopirox are the most widely applied antidandruff actives. Zinc pyrithione is typically used at a level of 0.5–1%, while octopirox is usually applied in a range of 0.2–0.5%.

Conditioning shampoos, sometimes called 2-in-1 shampoos, were introduced to global markets in the late 1980s. A conditioning shampoo is designed to deposit conditioning actives onto hair while washing off dirt at the same time. In order to make this happen, technology innovations were made in several areas: (1) stable dispersion of the water-insoluble conditioning actives such as silicones and conditioning oils; (2) efficient deposition of the conditioning actives onto hair; and (3) even distribution of the conditioning actives on hair surface.

Shampoo is generally used by applying it to wet hair, massaging the product into the hair, and then rinsing it out thoroughly. While some consumers may follow a shampooing with the use of hair conditioner, there are still consumers who may only use shampoo as daily hair washing and conditioning product. Hair conditioning effects such as making hair smooth, soft, easy to comb, etc. are expected from a shampoo by these consumers at both wet hair and dry hair stages. Wet hair conditioning of shampoo is mainly delivered by a colloid structure called coacervate formed by cationic polymer and anionic surfactant in water. On the other hand, dry hair conditioning is primarily the result of depositing silicones and conditioning oils on hair surface.

Coacervation is a unique type of electrostatically driven liquid–liquid phase separation, resulting from the association of oppositely charged ions.14–16 Coacervate formed during water dilution of shampoo while rinsing involves cationic polymers such as cationic cellulose or guar, and the anionic surfactants in shampoo (Fig. 36.3).8 Anionic polymers such as Carbomer also can be used sometimes in addition to the anionic surfactants to enhance coacervate formation. Functioning as a cushion, the water-containing coacervates provide nonsqueaky hair feel during rinsing and protect the wet hair from being damaged (Fig. 36.4).6

Silicones and/or conditioning oils are usually formulated in a conditioning shampoo to provide smoothness, softness, and shine to dried hair. The hair surface lubrication effect is the basic reason for using these oils. One feels that hair is smooth because of lowered friction between the surfaces of hair and hand skin. When interfiber friction between hair fibers is reduced, there is less resistance to movement, so people may feel that hair is soft and easy to comb. Furthermore, alignment of hair can be improved by the same mechanism, allowing better reflection of hair surface to light, giving shiner looking hair.

Silicones such as dimethicone, dimethiconol, and amodimethicone are the most widely applied oils for conditioning dry hair. Its low surface tension, high hydrophobicity, and variety of molecular weights or viscosities make silicone unique among all of the conditioning oils. A comparison between silicone treated and untreated hair surfaces is shown on Fig. 36.5.6 It is clearly observable that hair surface treated with silicone becomes smoother and covered with a thin protective layer. This is also the main reason for the color-protection effect claimed by some shampoos for consumers who color their hair.

In shampoo, silicones are often applied as preemulsified emulsions for better dispersion in the product. A variety of silicone emulsions are currently available from the silicone manufactures. Optimization of internal phase viscosity and particle size of the silicone droplets in emulsion is critical when selecting appropriate silicones to use. Measurement of hair friction or combing force is a typical tool used to screen silicones for their hair conditioning effect. Quantifying its deposition amount is also important to determine if a silicone is efficient in a given shampoo formula.17

Sulfate-based anionic surfactants, such as sodium laureth sulfate and sodium lauryl sulfate, and silicones have been the most applied ingredients in hair shampoo over the decades. However, recently sulfate-free and silicone-free shampoos are becoming popular in some markets. Consumers select sulfate-free shampoos for lower chance of skin and eye irritation or contact allergy. Some consumers also believe that silicone-free shampoo is a healthier or more environmentally friendly way to choose.

Sulfate-free shampoos and silicone-free shampoos may not be simply achieved by removing these ingredients from the shampoo, requiring new technology innovations. First, to be sulfate-free, low-irritation surfactants are needed to replace sulfate-based surfactants. Several classes of amino acid derivatives are often used for this purpose (Table 36.3). These amino acid-based anionic surfactants are reported to be milder than the traditional sulfate-based ones.18–20 However, other than higher in cost, these amino acid-based surfactants are often found less efficient in building viscosity when used as a primary surfactant in shampoo. The large head group of the amino acid-based surfactants is an unfavorable factor in forming extensive wormlike micelles for high viscosity.21 Adding sodium chloride usually is not highly effective in increasing viscosity of the amino acid–based surfactant systems. In fact, most of the sulfate-free shampoos sold in market have relatively low viscosity compared with the traditional shampoos.

Table 36.3. Amino Acid-Based Anionic Surfactants

Amino acid Structure
Glutamic acid
Aspartic acid
Glycine
Methylalanine
Methyltaurine
Sarcosine
R, lauryl, cocoyl; M+, K+, Na+, TEA+.

Thickening approaches are required to help build viscosity of the sulfate-free shampoos. Optimization of cationic polymers is the first option to explore. Molecular weight and charge density of cationic guar or cationic cellulose have a big impact on shampoo viscosity. Solution viscosity of the polymer per se is a useful parameter to which to refer, although there is not always a linear relationship with the viscosity of the final product.

Using amphoteric or nonionic surfactants as cosurfactants to balance the micelle packing parameter is another effective way to manipulate shampoo rheology.22–25 Cosurfactants that are often used include cocamidopropyl betaine, cocamide MEA, cocamide DEA, lauramide MEA, lauramide DEA, cocamide methyl MEA, laureth-3, PEG-2 laurate, PEG-150 distearate, PEG-120 methyl glucose dioleate, PEG-160 sorbitan triisostearate, butylene glycol laurate, etc. Optimization of the ratio between anionic surfactant/amphoteric surfactant/nonionic surfactant is critical to obtain optimal viscosity.

Polymeric thickeners such as xanthan gum, hydroxyethyl cellulose, hydropropyl methylcellulose, etc. also can be added to increase shampoo viscosity. However, overdosage of these thickeners may cause negative hair feel. Sometimes pH also has an impact on viscosity of amino acid–based surfactant systems. Therefore, optimization of the pH range needs to be considered.

Other than the difficulty in gaining viscosity, amino acid–based surfactant systems can generally deliver equal or higher lathering and conditioning performances versus sulfate-based surfactants.
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Hair conditioner is a hair care product used to improve the feel, appearance and manageability of hair. Its main purpose is to reduce friction between strands of hair to allow smoother brushing or combing, which might otherwise cause damage to the scalp.