Chemical Treatments of Hair, Hair Coloring and Bleaching

 Chemical Treatments of Hair

Chemical Treatments are the leading cause of hair structure changes and ultimately hair damage, but they also drive dramatic changes to either color (e.g. permanent coloring) or style (e.g. perming, straightening). Some people accept the damage tradeoffs for the desired benefits. Damage from these treatments is not just of a higher category but since all chemical treatments results in a breakdown of hairs protein and lipid structures, they render hair more susceptible to subsequent damage from physical and heat processes. Some people often will moderate their habits and practices once they start employing chemical treatments such as coloring by reducing washing frequencies and moderating heat implement temperatures.

 

Hair Coloring and Bleaching

Hair coloring is the most frequent chemical treatment worldwide. Forty percent of women color their hair in the United State, 46% in the United Kingdom and 49% in Japan. Hair coloring is increasing in popularity in large population countries such as China, Brazil and India. The coloring process involves aggressive chemistry designed to lighten the hair bleaching the natural pigments melanin and complex chemistry designed to from artificial color within the hair. It is the combination of lightening and color information that gives the final shades, but is is the oxidant chemistry that is the main source of hair structure changes and ultimately hair damage.

There are two reactive species formed during the coloring process that have significant impact on hair health via several mechanisms. The first species (Figure 1.32) is the perhydroxyl anion (HOO) which is formed from hydrogen peroxide and ammonia at the high Ph used in colorants. This species is crucial for bleaching melanin, so there is always a tradeoff between coloring performance and damage caused. 

 

The perhydoxyl anion is responsible for two major chemistries that directly impact hair health. The first is removal via perhydrolysis of the surface lipid layer (f-layer or 18 methyleicosanoic acid) that is present on each cuticle cell (Figure 1.33).

 

The lipid provides a protective hydrophobic coating which reduces friction forces, especially when hair is wet, and give hair its smooth and soft feel. Once removed after coloring, the surface properties of hair dramatically change, with wet friction increasing significantly in addition to loss of soft feel and shine.

Once friction is increased, damage to hair from combing and brushing also significantly increases, with an accelerated formation of knots and tangles. This additional damage can be reduced with use of conditioners, but removal of the hydrophobic lipid layer also has consequence of reducing deposition levels of conditioning activities, especially silicones. Over the last few years this chemistry has been well explored and strategies to reduce the impact of surface lipid removal via coloring have been introduced. There has been an explosion in the identification of new silicone materials that will have an improved deposition profile on chemically colored hair.

The second chemical effect that the perhydroxyl anion will perform is to break disulfide bonds of the cross linking amino acid cysteine to form cystic acid (Figure 1.34). as a consequence of this breakage, the tensile strength of hair is decrease, and increased protein degradation and loss after washing can be measured. This will potentially be noticed as increase breakage, especially at hair tips where hair may have been exposed to several coloring treatments. 

 

The second reactive species is the highly reactive hydroxyl radical (HO*) which is formed during the reaction of hydrogen peroxide and any low levels of metals such as copper and iron present on hair. In most cases this is an unwanted side reaction that can be avoided by use of specific products, e.g. products that contain chelates which specifically target any copper in hair and prevent formation of highly reactive hydroxyl radicals. This chemistry is catalytic; i.e. low levels of copper will generate multiple hydroxyl radicals. Hydroxyl radicals will not specifically target any part of hair but will react with both proteins and lipids, causing degradation of these structures ultimately leading to easier breakdown with combing. Brushing etc…

All hair types will be impacted in a similar way but those using lighter shades such as extra light blonds will generally have more damage, mainly driven by higher levels of hydrogen peroxide used to achieve the lighter shades.

Hair damage many be lower for those coloring in the salon versus at home, not because of different chemistry being used but due to more skilled application methods. In the salon, the stylist will apply color to hair roots on the regrowth followed either by applying the same color to remaining hair for the last 10 to 15 minutes of total treatment time or using a lower hydrogen peroxide shade on the min and tips. At home, color may be applied over the whole head, giving a less even color and more cumulative damage.

Hair damage is significantly higher for those looking for a more significant shade transition from dark to light, where hair bleaches are use. These bleaches typically come as powders that contain per sulfate salts and silicates to provide alkalinity. These are mixed with hydrogen peroxide, forming chemistry that will significantly bleach melanin in dark hair or performed dyes. The mechanism of bleaching is via formation of highly reactive free radicals which do an efficient job of bleaching melanin but also cause damage to keratin, leading o loss of tensile strength and also making hair vulnerable to subsequent combing and brushing damage. Hair damage can be minimized by only using this chemistry for highlights (i.e. only selected strands) or applying for newly grown roots (Figure 1.35).