Evidence based information
Written by Medical editorial team head SIAHMSR
Medically reviewed by Dr. Sanjana V.B

Impact of styling processes and chemical treatment on hair

Role of hair conditioners- A research based study

   For intensely moisturizing and imparting glow to dry frizzy hair conditioners are often recommended and used on hair. Both natural as well as chemical based conditioners are available for use in the global market. Do you know how do these hair cosmetics work?  To understand the effect of conditioners on hair it is important to learn the structure and behavior of hair shaft.

Structure &behavior of hair shaft

 The hair shaft comprises cuticle, cortex and medulla. The cuticle is a chemically resistant region and consists of flap overlapping scales (keratinocytes) . The shape and orientation of the cuticle cells accounts for the differential friction effect in hair. The frictional work required to slide one fibre over another is greater in the direction tip-to-root than the converse; this is the so-called differential friction effect (DFE)

The cortex constitutes the major part of the of the human hair, and it is formed by elongated, fusiform cells and contains protein and melanin granules. The cortex cell also contains spindle-shaped macrofibrils.

The medulla is present in coarser type hair such as grey hair, thick hair and beard hair, and it is absent in fine hair of children. The medulla has crucial role in the splitting of hairs.

     Ethnicity has certain role in determining hair behavior and structure. The medulla is more prominent in the coarser hair of Asians than Caucasians. The cuticle is generally formed by 6–8 scales thick for Asians, and it is lower in Caucasians and even less in African hair. The thin cuticle layer makes African hair more vulnerable to breakage.

  Each cuticle cell contains a thin proteinaceous membrane, the epicuticle. The epicuticle is covered with a lipid layer that includes the 18-methyl eicosanoic acid (18-MEA) and free lipids. Beneath the cuticle cells membranes there are three layers, all containing heavily cross-linked protein, mostly cystine, the A-layer, the exocuticle or B-layer and the endocuticle. The first one contains the higher amount of cystine, and the third one contains the lowest. The 18-MEA is responsible for the hydrophobicity of the hair and its removal by alkaline chemical cosmetics procedures may damage hair by increasing hydrophilia.

The cell membrane complex (CMC)

It is intercellular matter that consists of cell membranes and adhesive material (cement) binding the cell membranes between two cuticle cells, two cortical cells and cuticle-cortex cells. The most important layer of the CMC is called the beta-layer, and it is considered to be the intercellular cement and it is sandwiched by other layers from each cell.

  Weathering of hair shaft & role of hair cosmetics in protecting hair

  The CMC and the endocuticle are very vulnerable regions to the chemical treatments such as bleaching, dyeing and hair straightening/perm procedures. Frequent  shampooing friction may disrupt the CMC.CMC fractures may be seen before the hair fiber is ruptured.

  Repeated rough washing, unprotected drying, friction actions, sunlight and alkaline chemical treatments lead to a decrease in the lipid content of the cell surface. These procedures may change its hydrophobicity to a more hydrophilic, negatively charged surface state.

    The cortex matrix is formed by crystalline protein of high cystine content. The cortex cell also contains spindle-shaped macrofibrils. The macrofibrils are arranged in a spiral form. Inside the microfibrils there are subfilamentous units called protofilaments, each contains short sections of alpha-helical proteins in coiled coil form. The alpha-helix is held coiled by chemical forces such as: Ionic forces, hydrogen bonds, Van de Waal forces and disulfide bonds. Hair straightening process consists on breaking the forces that hold the coil, allowing it to be stretched.

   If the rupture of the chemical bonds is followed by curling the hair, it is called “perm,” meaning permanent curling. The process of reduction the hair involves hair swelling and very alkaline substances such as sodium or lithium hydroxide, guanidine, ammonium thioglicolate[ pH higher than 9.0.]

All this styling processes on hair lead to splits or cracks to the endocuticle and the CMC, but the major damage to hair after using hair reducing products is indeed due to misuse of the products and lack of care during combing hair in the reduced state.

Hair damage caused by the use of chemical procedures can be minimized, avoided or repaired by the correct use of hair care products. Hair cosmetics may enhance hair hydrophobicity, strengthen the cuticle and minimize electrical charges and friction forces.

In the wet condition, virgin hair can be stretched by 30% of their original length without damage; however, irreversible changes occur when hair is stretched between 30% and 70%. Stretching to 80% causes fracture. Hair is porous and damaged hair is intensely porous. Water absorption causes the hair shaft to swell.

 Excessive or repeated styling procedures such as chemical treatment, grooming habits, and adverse environmental exposure can affect hair texture and ultimately result in hair breakage.  All these changes of hair shaft due to chemical and environmental exposure can be seen microscopically as “weathering” of the hair shaft. This may lead to tangling, and frizzing of hair.

Weathering is the progressive degeneration of hair from the root to the tip of the hair. When the hair is extremely weathered and chemically treated, there may be scaling of the cuticle layers, removal of the 18-MEA and cuticle crack in the structure of shaft.

 If the cuticle is removed, the exposure of the cortex and further cortex damage may lead to hair fiber fracture.

The use of hair cosmetics may restore hair cuticle damage and prevent hair breakage by reducing friction and water pick up

CONDITIONERS- How do they act on the hair to help dryness& frizz?

 Conditioners are hair cosmetics used to decrease friction, detangle the hair and reduce frizz. Conditioning your hair may help to remove dryness and impart shine and glow. Conditioning is very important for revitalizing your damaged, dry, frizzy hair. It also strengthens the hair by preventing hair breakage.

  Conditioners act by neutralizing the electrical negative charge of the hair fiber by adding positive charges and by lubricating the cuticle that reduces fiber hydrophilicity.

   Conditioners contain anti-static and lubricating substances that are divided into 5 main groups: Polymers, oils, waxes, hydrolyzed amino acids and cationic molecules.

 The most active and commonly used conditioner agent is a silicone. There are different types of silicones with different deposition, adherence and wash out capacity which may account for the different performances of the conditioner.

  The ideal conditioner maybe capable of restoring the hydrophobicity of the fiber and neutralize the static electricity depending on its capacity of entering the fiber. The conditioner may reach the cuticle surface or the inner part of the cortex after applying. Smaller molecules can reach the cortex. Larger ones act on the cuticle. Low molecular weight polypeptides (<10.000 Da) can diffuse into hair. Bigger molecules (500.000 Da) can diffuse into the cuticle.The preferred route is intercellular diffusion or diffusion through the non-keratin regions, although intracellular diffusion may also occur. Higher molecule weight polymers (<600.000 Da) may be absorbed on the surface of the hair shaft.

   Cationic ingredients such as cationic polymers are very popular in hair products. They can be so substantive to the hair that they can be difficult to remove. They are highly substantive to hair because of the hair's low isoelectric point (pH - 3.67). Any cosmetic with higher pH bears a net negative charge on the hair surface, and therefore cationic charges (positive) are attracted to it. Also, Van der Waals forces and entropy are necessary to bind the molecule to the hair fiber, and they must be resistant to rinsing with water. Examples of such polymers are: Benzyl dimethyl ammonium chloride and distearyldimonium chloride.

  It is common to use cationic ingredients in many shampoos' formulations with anionic surfactants in order to result in charge neutralization forming a cationic-anionic complex, a neutral hydrophobic ingredient. Therefore, we can understand that the interaction between the ingredients is more important than the ingredient alone.

 It is very common to think that a new release product that contains a certain ingredient has the magic ability to transform dull hair into shiny and smooth hair. Often in new products, the major ingredients do not change, but the capacity of the ingredients to interact makes the product work better.

 Bleached and chemical treated hair have a higher affinity to conditioning ingredients because they have a low isoelectric point (higher concentration of negative sites) and are more porous than virgin hair.

Functions of the conditioner

·       Restore hydrophobicity

·       Seal the cuticle

·       Reduces  frizz, friction

·       Improves shine, smoothness and manageability.

Hair shine improving and protecting ingredients of hair cosmetics & conditioners

Silicones

   Silicones are hybrid (inorganic-organic) inert, heat-resistant and rubber-like polymers derived from cristal quartz. Silica (silicon dioxide) common in sandstone, beach sand.

 Dimethicone is the most commonly used silicone in hair care products. It is the main ingredient of the two-in-one shampoos. Other ingredients commonly used are: Aminosilicones, siloxysilicates, anionic silicones and others.

   Some silicones can improve the shine of hair fiber by reflecting the light. Dimethicone has the effect of protecting the hair shaft from abrasive actions while siloxysilicates increase hair body. Polysiloxane polymers may re-cement lifted cuticle scales and prevent damage from heat.Amino functional silicones are cationic substances but not necessarily are more substantive to the hair than dimethicone, depending on the size of the molecule and the charge of the system.

   Dimethicones are hydrophobic, so they adsorb better on virgin hair and root rather than tips. To improve the deposition of dimethicone on chemical treated and damaged hair , the hair care products  often use cationic bridging agents which can increase  affinity between hair and the silicone.

Protein hydrolysates

 These ingredients have been known to protect hair against chemical and environmental damage. Many types of protein hydrolysates from plants and animals have been used in hair cosmetic. Keratin  hydrolysates  are obtained from nails, horns and wool.  Recently hydrolyzed hair keratin, feather keratin peptides have been obtained by enzymatic hydrolysis using Bacillus species in submerged fermentation. The hydrolysed protein derived from feather was deposited on the cuticle scales, and helped sealing the cuticle especially after heating with a flat iron, improving hair color and shine.

   A higher amount of protein is often deposited on chemical treated hair, especially bleached. As the hydrolyzed amino acids are positively charged, probably the negative charge of the damaged hair attracts the positively charged molecules neutralizing the electrical charges and diminishing frizz and friction.

   Keratin hydrolysates are usually prepared from keratin-containing animal parts, such as feathers, horns, hoofs, hair and wool, collected from discarded materials.

Some industries or brands  have developed products that use a complex of non-animal  source free amino acids derived from wheat, corn and soy proteins to mimic the natural composition of keratin. However, keratin is an irreplaceable protein in respect to its mechanical and protective properties, and the using of amino acids do not replace or restore the damaged molecule structure.

References

1.      International Journal of Trichology. 2015 Jan-Mar; 7(1): 2–15.doi: 10.4103/0974-7753.153450  PMCID: PMC4387693 Hair Cosmetics: An Overview  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4387693/

2.      Robbins CR. Chemical and Physical Behavior of Human Hair. 4th ed. New York: Springer; 2013. [Google Scholar]

3.      Dawber R. Hair: Its structure and response to cosmetic preparations. Clin Dermatol. 1996;14:105–12.  https://pubmed.ncbi.nlm.nih.gov/8901408/

4.      Robbins CR. Chemical and Physical Behavior of Human Hair. 4th ed. New York: Springer; 2013. [Google Scholar]

5.      Villa AL, Aragão MR, Dos Santos EP, Mazotto AM, Zingali RB, de Souza EP, et al. Feather keratin hydrolysates obtained from microbial keratinases: Effect on hair fiber. BMC Biotechnol. 2013;13:15 https://pubmed.ncbi.nlm.nih.gov/23414102/