Girls usually have one favorite shampoo brand that they
swear by, and I’m no exception, but on this trip I have used several different
types of shampoos, from the Fuge’s “2-in-1 shampoo and body wash” – which I
thought was really questionable – to a shampoo for “frizzy, curly, thick hair”
from an Italian pharmacy. I wondered if all shampoos function essentially the
same way. How does shampoo work?
I can't do without my Garnier
We all know how soap works from, like, day one of general
chemistry. Well, shampoo works
practically the same way (no surprise there) but there’s more chemistry beyond
that. Shampoos contain several key
ingredients that are necessary to clean hair without damaging it. Hair glands
at your scalp release an oily substance made of fats and wax called sebum,
which prevents the scalp from drying out. This oil accumulates dirt pretty
quickly though, which is why you need to shampoo your hair, since water alone
cannot remove dirt from oil.
Shampoos use cleaning agent called surfactants that produce
the foam/lather that occurs during shampooing. While there are many different
molecules that can be used as surfactants, they all have a similar composition:
a hydrophilic end and a lipophilic end. Remember from soap – the lipophilic end
is attracted to the nonpolar oils, while the hydrophilic head of the molecule
is attracted to the polar water molecules. Surfactants encase oil molecules and
separate them from each other, then the polar heads on the outside attract water
to wash away the dirt and oil.
Surfactants can differ based on the length of their nonpolar
hydrocarbon chain, which can range anywhere from 8 to 18 carbons. Shorter
chains have stronger oil-removing capabilities, while longer chains are more
mild but less lathering. Shampoos use what are called anionic surfactants,
which have a negative charge when ionized. The most common of these are sodium
laureth sulfate and sodium lauryl sulfate – these are used in popular shampoos
such as, say, Herbal Essences Hello Hydration, of which Bhavesh claims to be a
fan for its Hawaiian coconut scent.
sodium lauryl sulfate
The only problem with this highly effective cleaning method
is that shampoos remove all the oil that protects hair, so this oil has to be
replaced. This is where conditioners come in! Conditioners contain essential
fatty acids which are the next best thing to replace the natural sebum. Hair is
composed of 97% keratin, which is a protein with a surface made of
negatively-charged amino acids. Therefore, conditioners contain what are called
cationic surfactants, which are positively charged when ionized. They will
cling to the negatively charged strands of hair, so they aren’t easily washed
off with water.
I looked at the ingredients in the conditioner that Carolyn
bought from the olive oil shop, and sure enough, the third ingredient listed
was cetrimonium chloride, which is the most common cationic surfactant. This
molecule has a single positive charge at its head, which binds to hair strands
and creates the smooth texture and prevents those pesky fly-aways.
Conditioners also contain some kind of silicone-based
ingredient that coats the hair to prevent it from drying out after shampooing.
The most common is dimethicone, which forms a slick coat around each strand of
hair in order to separate the strands, detangling hair and making it easier to
comb. Cetrimonium chloride is also an emulsifying agent, so it helps disperse
the water-insoluble silicone oils into the conditioner.
dimethicone
So now you know why it's important to use conditioner after shampoo. Especially for those of us unfortunate enough to have curly hair, which without fail will turn into some kind of Albert Einstein look when we don't use conditioner. Not a sight anyone wants to see.
Oh and one more thing of dire importance.... FORZA AZZURRI!!!! VIVA ITALIA!!!
<----- that's the face of a champion if I've ever seen one
Sources:
Bhavesh brought up an interesting question about 2-in-1 shampoos (since he's weird and hates separate hair conditioner). Chemically, it doesn't make sense because conditioners are oils, but shampoo surfactants are designed to remove oils, so how exactly can the two work simultaneously? The answer is pretty clever.
ReplyDeleteThese 2-in-1 shampoos contain micro-droplets of silicone held in suspension by polymer encasings. These polymers bind to the surfactant molecules in the shampoo. These silicone-containing polymers are inactive during the lathering period of shampooing. But when you rinse your hair, the water interacts with the shampoo such that the polymers are detached from the surfactant molecules. Since the polymers and the silicone oils are insoluble in the water, they are not washed away with the surfactants. Instead, they precipitate out of the shampoo mixture and coat your strands of hair.
So, technically, 2-in-1 shampoos should be as effective as a separate shampoo and conditioner. But that's not going to stop me from using actual conditioner!
http://www.rsc.org/chemistryworld/issues/2005/january/taketwobottles.asp