The Science of Hair type

The Science of Hair Type

 

Hair is a remarkable bio-composite material with a highly complex structure. The bewildering variability in appearance, properties and behavior may instinctively suggest inherent differences in this structure as a function of “hair type” - but what technical features constitute “hair type”?

 

Hair from individuals of different ethnicity can possess especially different appearance – which has acted as the starting point for much of the historical work in this area. Yet, outside of shape, thickness and color, there appears little evidence for significant compositional and/or structural differences. This said, differences in the reactivity of hair from different individuals has long been recognized. Application of a permanent wave to one person’s hair may produce the desired result; while the exact same product and procedure may yield a wholly ineffectual outcome on the next. Clearly, some unrecognized structural factor is in-play.

 

We are investigating this problem with a variety of measurement techniques, including: reactivity to perms, swelling, penetration rate experiments, mechanical properties, water absorption and differential scanning calorimetry (DSC).

Histograms for Fiber Diameter as a Function of Hair Type

Hair is a highly variable substrate – which prompts a need for classification, while
simultaneously complicating this process. For example, while Asian hair is widely considered to be
thicker than Caucasian hair, huge variation exists in dimensions of fibers from each ethnicity.

Asian hair is generally considered to be least elliptical in cross‐section – but again,
considerable variability exists.

Reaction times for a common perm solution with hair from the heads of 9 different panelists.

Swelling for Single Source Hair Fibers as fn of RH

We speculate that differences in the swellability of hair from different individuals might be a
reason for differing reaction rates with a common chemical treatment.

Swelling for Single Source Hair Fibers as fn of RH

We speculate that differences in the swellability of hair from different individuals might be a
reason for differing reaction rates with a common chemical treatment.

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