|HAIR PHYSIOLOGY
The appearance and function of the hair shaft can be affected by porosity, elasticity, and texture.
Porosity
Porosity is defined as the hair shaft’s ability to absorb moisture. Without cuticular damage, the hair shaft is relatively impermeable to water and other substances. With changes caused by permanent waves, coloring, temperature or pH changes, the cuticle can be rendered more vulnerable permitting penetration and damage to the cortex. With repeated injury, the cuticle can be rendered permanently damaged allowing moisture to escape and making the hairy dry, brittle, and exhibit split ends.
 
Elasticity
Elasticity measures the tensile strength of the hair with a normal hair able to stretch to about 1 and 1/3 its original length with healthy hair able to support a 100-g weight without breaking. Elasticity is dependent upon a healthy cortex, and a hair shaft that has poor elasticity can break easily with grooming and with product application.
Texture
Texture is affected by two determining factors: the thickness of the hair shaft and the feel of the hair itself. Wiry hair possesses its characteristics by virtue of the tight adhesion of the cuticle to the cortex and the flat arrangement of the cuticular scales. Wiry hairs may be more resistant to chemical alteration.
Permeability
Permeability is affected by the degree of porosity, elasticity, and texture of the hair shaft with the porosity and texture having the major influences on permeability. Porosity clearly plays a greater role than texture. However, fine hair will absorb more applied product than coarse hair given the same degree of porosity. Coarse hair with great porosity will still have greater permeability than fine hair with low porosity.
SHAMPOOS
Shampoos have made major advances since they were originally introduced. Besides simply cleaning the hair, they can also repair and protect hair as well as provide luster and shine with certain additives.
Soap Shampoo
This is the original hair cleanser. This alkali-based product also contains oils and salts of fatty acids. Soap shampoos are effective cleansers and are inexpensive. However, they form a scum layer on hair when hard water is used (which accounts for the majority of water out there) so soap shampoos are relatively infrequently used today.
Detergent Shampoo
In the 1950s, detergent shampoos were developed since most people live with hard water. They are composed of principal surfactants for detergency and foaming power, secondary surfactants to condition the hair, and additives. The detergent shampoo works by transferring dirt with a lipophilic component to the rinse water with a hydrophilic component.
Anionic Surfactants
Anionic surfactants are the principal detergents used in detergent shampoos. Sodium lauryl sulfates and ammonium lauryl sulfates are very strong and alkaline cleansers but may be too irritative in individuals with chemically damaged hair. Disodium ricinoleamide MEA-sulfosuccinate may be a suitable alternative to these harsher agents but generally leave the hair in poor condition and are associated with a higher incidence of allergic contact dermatitis. Triethanoloamine (TEA) salts of alkyl sulfates are more easily tolerated and can be mixed with stronger detergents. Sarcosines clean poorly but leave the hair in better condition. Laureth sulfates are less irritating than lauryl sulfates but do not clean as vigorously.
Nonionic Surfactants
In general, nonionic surfactants act as secondary surfactants by increasing the quality of the lather, viscosity, and solubility. Examples are ethoxylated fatty alcohols, ethoxylated alkyl phenols, ethoxylated fatty amines, ethoxylated fatty amides, sorbitol esters, polyglycerol ether and amine oxide.
Amphoteric Surfactants
Amphoteric surfactants contain a balance of both positive and negative charges. They are very gentle cleansers and are the major components of baby shampoos. They are gentle in their cleansing and do not irritate the eyes. Examples include N-alkyl-amino acids, betaines, and alkyl imidazoline compounds.
Additives
Additives are used to provide other benefits other than cleansing. Beautifiers like hydrolyzed animal proteins are used to repair split ends by electrostatic attachment to the damaged hair. Thickeners like sodium chloride are used to give more viscosity to the shampoo product. Sequestering agents like polyphosphates and ethylenediamineetetraacetic acid keep calcium, iron, and magnesium salts from precipitating on the hair shaft. Preservatives like formaldehyde are used to prevent bacterial contamination to a water-based product like shampoo. Aesthetic additives help achieve the desired color and fragrance to improve marketability of the product. Tar, selenium sulfide, zinc pyrithione, salicylic acid, sulfur, and ketoconazole are therapeutic additives to treat conditions like psoriasis, seborrheic dermatitis, and dandruff.
Shampoos for Different Hair Types
A shampoo formulated for oily hair has a higher percentage of anionic surfactants, and a shampoo for dry hair would have a weaker anionic component. Limp or fine hair must be treated with shampoo that has fewer conditioners that can weigh down the hair but instead have more protein additives that can provide extra body. Permed or damaged hair must have a higher percentage of amphoteric surfactants or non-ionic surfactants to preserve the more vulnerable cuticle.
CONDITIONERS
Conditioners are used to increase manageability and shine to the hair and include rinses, cationic detergent conditioners, film-forming conditioners, and protein-based conditioners
Rinses
Vinegar and lemon were the earliest rinses used to combat the soap film left by early soap shampoos. Wax and paraffin have been used to coat the cuticle so as to limit static cling. Balsam is perhaps the best product in this category for that purpose.
Cationic Detergent Conditioners
Quaternary ammonium compounds like stearalkonium ammonium chloride can improve the manageability and shine of the hair. These negatively charged products adhere to the positively charged keratin fibers leaving a coat on the hair that can add shine and body.
Film-Forming Conditioners
Polyvinyl pyrrolidone (PVP) and others can attach to the quaternary ammonium compounds and thereby add body, viscosity, and shine to the hair as well as diminish tangling. These products can attach to the negative charge of the hair shaft at a point of a broken cuticle. Over time, these products can build up and weigh down fine hair (which they should not be used on). Strong anionic detergents can easily strip the hair with this type of conditioner.
Protein-Based Conditioners
Protein-based conditioners are very popular, as the proteins contained within can attach to the inner hair shaft at cuticular breaks, especially in processed hair or with split ends. Proteins can be derived from animal proteins, eggs, placenta, collagen, and keratin.
Combination Conditioner-Shampoo
In general, combined shampoos and conditioners do not work well, as the hair is not cleaned or conditioned well enough. However, in 1994, Rushton et al. found that dimethicone could be used to condition the hair in a 2-in-1 product which would not be removed with the shampoo until a subsequent session of shampooing.
STYLING AIDS
Styling Lotions and Gels
Lotions (thinner) and gels (thicker) are applied to towel-dried or dry hair to provide more shape to the hair with gels being able to create stiffer hair arrangements.
Mousses
Mousses are distinct as they foam and can provide styling to the hair but not be as heavy as gels.
Hair Spray
Current hairsprays contain PVP that is a hydroscopic resin that provides holding power until contact with water. The copolymer concentration determines the degree of hold. Vinykl acetate can be added to waterproof the hair and thereby limit the sagging with perspiration or water exposure.
PERMANENT WAVES AND RELAXERS
The shape of the hair (curly, straight, and kinky) can be changed by breaking and reforming the disulfide bonds within the hair shaft through the use of heat or chemicals.
Mercaptan Permanent Waves
Base Permanents
The use of ammonium thioglycolate is used in a cold process to saturate wet hair when the hair is wrapped over curlers or rods so that the hair hardens to the new shape over 5 to 20 minutes. This technique can be undertaken at home and provides a tight curl for 3 to 5 months.
Acid Permanents
Glycerol monothioglycolate is an acid-based product that is much gentler on the cuticle and can be used on color-processed hair. The acid-based perm requires heat to activate it like a blow dryer. In general, this kind of perm has a higher incidence of dermatitis, does not provide quite as tight a curl, cannot be used with African hair, and lasts a shorter time of 2 to 3 months.
Relaxers
Hot Combs
This is the most common type of relaxer used in which oil is applied to the hair shaft and combed through with a hot comb (300 to 500 degrees F) until the hair is straight. It is most commonly used in African-American children and can be repeated every 2 weeks and lasts until the next shampoo. The major disadvantage is the potential for hot comb alopecia.
Permanent Wave Relaxers
The two types of relaxers are sodium hydroxide (lye) and the guanidine/lithium hydroxide (no-lye). Lye relaxers are used exclusively by professional hairdressers, whereas no-lye relaxers can be used by both professionals and at home. Lye relaxers may cause more burn injury but are more effective in straightening the hair. Permanent hair loss with lye relaxers is unlikely as only the superficial follicle is injured.
COLORING AGENTS
Temporary Hair Color
Temporary dyes are derived from the textile industry and are used more for fun or for a party, as they are washed out with the next shampoo. These dyes can also soil clothing or bedsheets and caution should be exercised.
Metallic Dyes
A gradual change from gray to brown or black can be witnessed with the application of metallic salts to the hair. The colorless lead salt converts to brownish oxides and sulfides. As the dyes precipitate on the outside of the cuticle, they can render the hair dull and brittle. The smell of sulfides that emanate from the dye can also be unpleasant. Also, the metallic coat over the cuticle prevents penetration of permanent waves or permanent color.
Natural Coloring
Henna provides temporary coloring that requires 4 to 6 shampoos to remove. Given the high incidence of asthma, this product has not been widely adopted. It does not preclude permanent waving.
Semipermanent Dyes
Low-molecular weight dyes like nitroaminophenols and aminoanthraquinones can penetrate the cuticle by virtue of their small size. Because they do not contain hydrogen peroxide, they cannot lighten hair. These dyes are washed out with shampoo after 4 to 6 times and can be used at home for someone contemplating a change of hair color but is undecided.
Permanent Color
The most common type of hair coloring is permanent or oxidative hair color. Primary intermediates (“para” dyes) are combined with hydrogen peroxide to yield imines. The imines are then combined with couplers to create indo dyes. After the reaction, the molecules are too large to pass out of the cuticle making the change permanent.
To lighten the hair color, a two-step process must be undertaken in which the hair is first bleached with hydrogen peroxide then recolored with a toner. Individuals who have undergone this two-step process are ineligible for permanent waves. After coloring, an acidic pH shampoo should be used to help the cuticle close.
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