|
Hair
dryers
Hand
held hair dryers (or hair driers, whatever) are very popular today.
First developed in the 1930s, hair dryers for home use did not
become
common place until after the Second World War. Old hair dryers
with heating elements had no thermostat on them which meant there
was
a risk of applying too much heat and even burning the hair.
Today, thermostats in modern hair dryers should ensure the heat
at the end of the hair dryer nozzle is no higher than 85 degrees
centigrade (153 degrees Fahrenheit).
 Hair dryers should be used with constant movement so the heat
supply is not focused on one area of hair for too long. If the
heat is
applied to just one small area for a long period of time the heat
will build up and may damage the hair. Without simultaneous manipulation
(brushing or combing) irreversible heat damage to hair occurs when
the temperature reaches above 150 degrees centigrade (300 degrees
Fahrenheit). Mild hair damage involves breakage of the outer hair
cuticle which gives hair a rough, dry look. More severe damage
can
occur when too much heat is applied to wet hair for too long. When
water is heated it expands in volume. When water is inside the
hair
fiber and heats up, it pushes on the hair fiber from the inside
and causes "bubbles" to develop in the hair. Surprisingly
enough this condition is called "bubble hair". Once
hair damage is done through overuse of the hair dryer there is
not much
than
can be done to repair it. The only option is to grow out and cut
off the damaged hair.
Hair
is always subject to some damage through any form of manipulation,
but when the hair is wet it is weaker and so more liable to damage
than when it is dry. The hair becomes more plastic and weaker still
when high temperatures are used. When you dry your hair with a
hair
dryer you should be gentle with your brushing or combing. Manipulation
with a brush or comb should be restrained and slow with constant
pulling,
not rapid, jerky, high force strokes. A cool temperature setting
on your hair dryer is preferable to a hot one.
You should not use your dryer to completely dry the hair. It is
better to leave the last dampness in the hair to dry naturally.
Hair holds water within the fibers in a reversible way. Typically,
the amount of water in hair fibers is 33 percent when hair is wet,
about 13 percent at 65 percent relative air humidity and an average
room temperature of 21 degrees centigrade (70 degrees Fahrenheit)
and zero if the hair is over dried with a hair dryer. If you over
dry your hair you are damaging it more than is necessary. The hair
will just take up water from the air until it regains an equilibrium
with the relative air humidity.
By following these procedures you
should significantly reduce the amount of damage done to your
hair.
|
