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Variations in hair structure
Scientists do not fully understand why the different types of hair
grow straight or curly or wavy. This is probably determined by several
factors, which may vary in their importance during life. This is
why some curly-headed children have straight hair later in life,
and vice versa. These factors include:
- the way the large bundles of keratin are arranged within each
hair shaft
- the position of the hair bulb in the hair follicle - in African
hair the bulb may lie to the side of the follicle, and so the
hair shaft grows out of the follicle at an acute angle
- irregular growth in the hair bulb - if it varies slightly to
one side or the other the hair may grow wavy
- the shape of the hair follicle, whether it is straight or curved
- the number of twists per unit length.
All hair, even the apparently perfectly straight hair of Asian
people, twists as it grows. The number of twists in a given length of hair determine how curly it is: the more twists there are,
the curlier it will be. Some African hair has 12 times as many twists per centimetre as Caucasian hair. |
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In Asian people the keratin bundles
in the hair are all straight. The hair shaft tends to be thick,
and almost completely round.
The keratin bundles in the hair of Caucasoid
people are a mixture: most are straight, some are wavy. The proportions
of the two types vary a lot. The hair shaft is usually oval in shape.
The tightly curled hair of African people
twists much more frequently than in the other groups. The hair shafts
are markedly oval in shape, with definite edges. The cuticle is
sharply kinked at the edges, and is especially easily damaged at
these points. This curious shape is the reason for the vulnerability
of African hair to all forms of physical and chemical trauma, and
its consequent need for extreme care in handling and very thorough
conditioning.
Straight hair sometimes becomes quite wavy
when damp, and wavy hair may become
Compare
these cross-sections of three hairs, all of different racial types:
(left) Asian, (centre) Caucasoid, (right) African
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