What
is hair fiber made of
The primary component of hair fiber is keratin. Keratins are proteins,
long chains (polymers) of amino acids. Keratin proteins form the
cytoskeleton (miniature skeleton within a cell) of all epidermal
cells. Keratin filaments run within a cell from the inside of the
outer membrane to weave a "basket" around the nucleus
of the cell. Keratins are a principle part of the cells in the epidermis,
hair, nails, feathers, hooves, horny tissues and the enamel of teeth.
Keratin accounts for 30% of the cellular protein of living epidermal
cells and 85% of cellular protein of the dead cells in the stratum
corunem (the scaly, dead or horny layer of the outer skin). In hair
fiber, keratin proteins comprise 65-95% of the total hair fiber
by weight. Each molecule of keratin is very small - about 10 nanometers
across. To give you a sense of how small that is, 10,000 keratin
molecules lined up side by side would cover the width of the average
terminal scalp hair.
There are several subtypes of keratin proteins, some are called
"soft" keratins and others are "hard" keratins.
Basically, soft keratins are found in the skin and are relatively
easy to break down whereas hard keratins are very resistant to degradation.
Hard keratins do not dissolve in water and they are highly resistant
to proteolytic enzymes. As you might have guessed, hair fiber is
mostly made from hard keratin proteins.
Hair contains a high amount of sulfur because the amino acid cysteine
is a key component of the keratin proteins in hair fiber. The sulfur
in cysteine molecules in adjacent keratin proteins link together
in disulfide chemical bonds. These disulfide bonds are very strong
and very difficult to break apart. These disulfide chemical bonds
linking the keratins together are the key factor in the durability
and resistance of hair fiber to degradation under environmental
stress. They are largely resistant to the action of acids but the
disulfide bonds can be broken apart by alkali solutions. This property
is exploited in perms and chemical hair straightening processes.
Alkali is used to break the disulfide bonds in the keratins and
make the hair weak. The hair is formed into a new shape and then
acid is applied to neutralize the alkali and enable the disulfide
bonds to reform. The reformed disulfide bonds hold the hair in its
new shape.
Some cosmetics manufacturers claim to make hair products that contain
keratin to strengthen hair or promote hair growth. However, the
cells in hair follicles make all the keratin protein that they require
from amino acids supplied via the blood. Eating keratin protein
does not help hair growth. Eating hard keratins as found in hair
fiber is pointless as they cannot be broken down and absorbed. The
keratins simply pass straight through the gut. It would be much
better to eat the constituent amino acids from which the hair follicle
cells can make keratin. However, it is extremely rare in North America
and Western Europe to have a deficiency in amino acids so severe
that it affects hair fiber quality. Topically applying keratin to
hair also has no long lasting effect. The keratins are mostly washed
away in the shampooing process.
What
amino acids are present in hair fiber
Below is a table of the amino acids present in normal human hair
in order of their quantity.
| Amino Acid |
Amount in residues
extracted |
| Cysteine |
17.5 |
| Serine |
11.7 |
| Glutamic acid |
11.1 |
| Threonine |
6.9 |
| Glycine |
6.5 |
| Leucine |
6.1 |
| Valine |
5.9 |
| Arginine |
5.6 |
| Aspartic acid |
5.0 |
| Alanine |
4.8 |
| Proline |
3.6 |
| Isoleucine |
2.7 |
| Tyrosine |
1.9 |
| Phenylalanine |
1.4 |
| Histidine |
0.8 |
| Methionine |
0.5 |
What
is the carbon, oxygen, hydrogen, nitrogen, and sulfur content
of hair In terms of raw elements, on average, hair is composed of 50.65%
carbon, 20.85% oxygen, 17.14% nitrogen, 6.36% hydrogen, and 5.0%
sulfur. Hair also contains trace amounts of magnesium, arsenic,
iron, chromium and other metals and minerals.
How
many atoms are present in the average hair fiber diameter
The average scalp hair fiber diameter is between 80-120 micrometers.
Hair fiber diameter varies depending on the location of the hair
follicle, the ethnicity of the individual and the activity of hair
diseases. An atom has a diameter 10 to the minus 10 meters. That's
0.0000000001m or 1 preceded by 9 zeros and a decimal point. So the
diameter of the average hair fiber is ... er , umm, er ... (extensive
counting of fingers and toes) ... 800,000 - 1,200,000 atoms.
So the cross sectional area of a hair fiber asuming the cross section
is circular (which is not always the case as curly hair as an oval
cross section while straight hair has a circular cross section)
contains 500,000,000,000 - 1,000,000,000,000 atoms. Remember the
area of a circle is pi times the radius squared.
What
is hair fiber made of references
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