Study Set Content:
which gives colors from yellow- red to red. The hair color of each individual depends on the preponderant type of melanin as well as its quantity and distribution in the skin and hair.
pheomelanin
a polymer of high molecular weight, insoluble in water and most solvents. It originates from melanocytes located in the basal cell layer of the hair matrix
Melanin
involves a complex sequence of chemical reactions corresponding to an oxidative polymerization catalyzed by certain enzymes.
Melanogenesis
¨ Melanin granules are distributed throughout the hair cortex but in greater concentration towards the
periphery
The color of hair is an optical phenomenon attributable to the ()() of incident light from various interfaces, especially the bulk of melanin contained in the cortex.
reflection and refraction
¨ Hair fibers are generally elliptical, with cross sections having minor and major axis ratio in the range of ()()
0.63 to 0.91,
he most elliptical being ()hair, the most circular () hair.
black , Asian
Resistance to ()()() are related to fiber diameter
longitudinal deformation, bending and torsion stiffness, and hold of set hair
The relationship between the constraint and elongation obtained follows a curve of three regions () according to the stretching force.
pre-yield, yield, and post yield
is a strong enough fiber. It behaves like reinforced wire.
hair shaft
is fairly fragile because of the highly twisted configuration and flattening as opposed to Asiatic hair
Curled black hair
The disruptive load for hair varies with age, peaking at about
20 years
The length of hair plays a role in
perception
A typical example is when the hair is cut short, people usually interpret the perception of stubbles as thickening of the newly produced()fiber.
hair
Instead of the soft feel of a non changing full head of hair, one now feels hair growing from
day to day
Another misconception among lay people may be so explained: a haircut does not influence hair growth; it is just becoming
noticeable
The intended desirable effects of cosmetics on hair are very wide and variable. Examples are:
¨ Cleansing ¨ Dyeing ¨ Perming ¨ Bleaching ¨ Straightening ¨ Dressing ¨ Setting ¨ Removing
Some desirable actions are not achievable without inducing damage to the () itself
hair fiber
Example: in permanent or oxidative hair dyeing a degree of damage to the () is necessary to introduce the dyes that are targeting the hair cortex
hair cuticle
When the hair cuticle is weakened it cannot be fully ()(figure 1), but some cosmetic agents may decrease the abnormal fragility and the rough feel of damaged hair. No better results can be achieved than by cutting away the damaged fibers and letting new hair growth proceed without new harsh procedures.
restored
