What Shampoo Does
Unless
you've been rolling around in mud, you probably don't have hair that is truly
dirty. However, it may feel greasy and look dull. Your skin produces sebum, a
greasy substance, to coat and protect hair and the hair follicle. Sebum coats
the cuticle or outer keratin coat of each hair strand, giving it a healthy
shine. However, sebum also makes your hair look dirty. An accumulation of it
causes hair strands to stick together, making your locks look dull and greasy.
Dust, pollen, and other particles are attracted to the sebum and stick to it.
Sebum is hydrophobic. It waterproofs your skin and hair. You can rinse away
salt and skin flakes, but oils and sebum are untouched by water, no matter how
much you use.
How Shampoo Works
Shampoo
contains detergent, much like you would find in dishwashing or laundry detergent
or bath gel. Detergents work as surfactants2. They lower the surface tension of
water, making it less likely to stick to itself and able to bind with oils and
soiling particles. Part of a detergent molecule is hydrophobic. This
hydrocarbon portion of the molecule binds to the sebum coating hair, as well as
to any oily styling products. Detergent molecules also have a hydrophilic
portion, so when you rinse your hair, the detergent is swept away by the water,
carrying sebum away with it.
Other Ingredients in Shampoo
Conditioning Agents
Detergents
strip away the sebum from your hair, leaving the cuticle exposed and
susceptible to damage. If you use soap or dishwashing detergent on
your hair, it will get clean, but it may look limp, lacking body and shine.
Shampoo contains ingredients that replace the protective coating on hair.
Silicones detangle hair, smooth the hair cuticle, and add shine. Fatty alcohols
help prevent static and fly-away or frizzy hair.
Shampoo
typically is more acidic than soap, so it may contain ingredients to bring down
the product of the pH. If the pH of shampoo is too high, the
sulfide bridges in keratin can break, weakening or damaging your hair.
Protectants
Many
shampoos contain additional ingredients intended to protect hair. The most
common additive is sunscreen. Other chemicals protect against heat damage from
hair dryers or styling aids, chemical damage from swimming pools, or build-up
from styling products.
Cosmetic Ingredients
Shampoos
contain aesthetic ingredients that don't affect how well the shampoo cleans
your hair, but may make shampooing more pleasant or affect the color or
fragrance of your hair. These additives include pearlising ingredients, which
add sparkle to the product and may leave a faint glimmer on hair, perfume to
scent the shampoo and hair, and colorants. Most colorants wash out with
shampoo, although some subtly tint or brighten hair.
Functional Ingredients
Some
ingredients are added to shampoo to keep it uniformly mixed, thicken it so that
it is easier to apply, prevent the growth of bacteria and mold, and preserve it
to extend its shelf life.
A Word About Lather
Although
many shampoos contain agents to produce a
lather, the bubbles don't aid the cleaning or conditioning power of the shampoo.
Lathering soaps and shampoos were created because consumers enjoyed them, not
because they improved the product. Similarly, getting hair "squeaky
clean" actually isn't desirable. If your hair is clean enough to squeak,
it has been stripped of its natural protective oils.
Source:
http://chemistry.about.com/od/howcleanerswork/a/How-Shampoo-Works.htm
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