Hair Strength Of The Human Hair
A single strand of hair can surprisingly support a weight of 100 grams without breaking. This unusual hair strength is attributed to the keratin protein of the cortex.
The long keratin molecules in the cortex are compressed to form a regular structure, which is not only strong but also incredibly flexible.
Most protein chains are made up of various mixtures of the same 20 or so amino acids. Keratin is unique in that its chains contain high concentrations of a particular amino acid called cystine. The proteins in the matrix of the hair contain the highest levels of cystine.
Every cystine unit contains two cysteine amino acids linked together by two sulphur atoms, forming a very strong chemical bond known as a disulphide linkage. Many disulphide bonds form down the length of the keratin chains, joining them together like the rungs of a ladder.
The disulphide bond is one of the strongest bonds known anywhere in nature.
This cross-linking by disulphide linkages between the keratin chains accounts for a large majority of the hair strength.
How hair gets its shape
The shape of a hair depends on several factors, including the shape of the hair follicle and its opening; these vary from one person to another and also between races.
This in turn has an affect on the hair types and colours that are found throughout the globe. As keratin hardens it is compressed into the shape of the hair follicle. The developing hair holds it shape by the influence of chemical bonds around it.
Hydrogen bonds-responsible for hair flexibility- are present in much greater quantities than disulphide linkages, but they are much weaker and more easily broken.
Whenever the hair becomes wet the hydrogen bonds are broken apart and allow the hair to be re-shaped, when the hair subsequently dries it will retain the new shape.
This wetting and breaking of the hydrogen bonds is infinite and allows hairdressers to create the many wonderful hairstyles, they can rely on this natural hair strength for their creativity.
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