The Process of Weathering, Sources and causes of Hair Damage

 

 The Process of Weathering

Hair is an exceptionally resilient structure able to withstand many differing traumas environmental, mechanical, physical and chemical. Hairs take from ancient Egyptian mummies and even from the bodies of our stone age ancestors appear remarkably well preserved even after thousand of years. In the twenty first century, in spite of this resilience, badly weathered hair is epidemic, particularly in the developed world. 

 

When hair first emerges from the scalp, the cuticle consists of up to ten layers of long scales. However, the cuticular layers are only 3 to 4 um thick and may have to last for some six years or more. Natural weathering involves a wearing away of the cuticle of the hair shaft, primarily from physical acts of grooming. Accelerated weathering occurs as a result of additional and excessive physical and most importantly, repeated chemical injury. This accelerated weathering, which is generally retardation of the proteins in the cortex. The later becomes increasingly unable to maintain the structural and homeostatic integrity of the hair and its most extreme, the hair proteins may unravel, causing split ends or breakage in the mid shaft.

Sources of Hair Damage

Major damaging sources include wetting, friction, sunlight, heat from drying and styling appliances, chemicals and heavy metals in swimming pools and even the home. Most devastating are chemical procedures notably bleaching, perming, relaxing and straightening.

Other insults are due to poor habits and practices, and include physical damage from brushing and combing and the use of excessive heat from styling implements such as blow dryers and flat irons. It is now recognized that poor brushing and combing techniques are more detrimental than previously though.

 

Causes of Hair Damage

The major causes of hair damage are environmental, physical, heat and chemical. These insults do not occur in isolation. The final damage to hair can be due to a combination of these factors, their frequency and intensity. If a woman possesses hair of 40 or 50 cm length, there may be four or five years of these cumulative insults. Most of these insults impact at the nano-structural level by causing changes to protein and lipid structures. The insults themselves cannot be detected but can be measured by techniques such as proteomics and lipidomics that identify the exact structural changes.

As a result, there any micro structural and single fiber changes that eventually will manifest as micro structural or bulk hair changes. As an increasing number of fibers lose cuticles, the cortex will eventually be exposed, which further reduces shine and will increase the propensity of hair to from split ends. As more protein damage occurs, the tensile strength of hair will decrease and eventually lead to breakage, which will then be noticed as additional hairs in the brush or lack of smoothness because of the broken ends.

Cuticle integrity of hair from ten individuals with 30 cm long hair, where the cuticle was assessed at the roots, midsection, and tips using an scanning electron microscopy (SEM). Fifty fibers were graded on a scale of 0 to 5 depending on the level of cuticle damage observed, and then the final grade calculated. Where the maximum possible score is 250. In addition, representative images are shown illustrating the cuticle degradation.

Micro structural changes to cuticle integrity that is easily measurable using SEM techniques and correlates well with the level of damage noticed. Nano structural changes are also measured from root to tip from individual ponytails, and specifically the degradation of proteins. These changes are not directly observable but will lead to a weakening of hair, making it more susceptible to further breakage. One manifestation of this protein degradation will be loss of tensile strength (i.e. how easily the fiber is broken).

Data from a set of 26 individual ponytails of 30 cm long where the protein degradation was measured by proteins loss. This measure involves shaking a small sample of hair in water for an hour and the total amount of protein eluted into solution quantified using the Lowery method. The data are for beak load averaged across all the root ends versus tip ends. Significant differences are observed between root valves and tip values.