Whether you rock sideburns or
baby-smooth legs, all shavers alike share
one thing in common: the existential
threat of razor sharp metal. Razor burn
and nicks and cuts are enough to make
some folks go full lumberjack, but for
the rest of us,
shaving cream packs the custom chemistry
needed to keep our precious skin safe
from harm. What is this miracle substance
you ask? Today, with the help of our
friend Ms. Beautyphile, we're taking a
closer look at this chemically
incredible foam. People have been shaving
for thousands of years. It's said that
Alexander the Great had his soldiers
shaved to stop beard pulling in battle.
But later on in the 1940s when beard
trimming was less of a military strategy,
brush and mug shaving soaps were used to
whip up a foam that helped make the
process a lot smoother. Then in 1949 a
game-changer hit the market. Aerosol
shaving cream was a smooth faced
revolution bringing new levels of
convenience and efficiency to the table.
Shaving cream does a lot more than just
lubricate your face to prevent nicks and
cuts. Its dense foam and tiny bubbles
lift hair away from your skin for a
closer shave while also telling you
where your razor's been. And lastly it
gets your face nice and clean because
shaving cream is actually just soap in a
can. But chemically speaking it's a soap
with a lot of thought put into it. Ms.
Beautyphile, why don't you give us a hand
and explain how? Soaps belong to a class
of molecules called surfactants that
have the ability to hold on to water and
oil at the same time. Here's an example
of what they look like. There's a fatty
acid on one side with a zigzagging tail
and a positive ion on the other. One side
is hydrophilic, meaning it loves water,
and the other side is hydrophobic, which
means it doesn't like water, but it's
attracted to oil. It's this special
quality that allows surfactants to scoop
up oily dirt and whisk it away with
water, getting you squeaky clean.
So if it's just soap then why can't we
splash some water on our face and do
this to get a nice foam to shave with?
You'll notice the bubbles from the bar
soap dissolve almost immediately. One of
the reasons shaving soaps are so much
better at creating that long-lasting
foam is that they're formulated for
optimal lather. When it comes to creating
great lather, part of the equation is the
ion in the hydrophilic head. A sodium or
potassium ion will give you a less dense
lacy air foam, while triethanolamine
will give you a creamier lather,
which is why triethanolamine is the
preferred choice when it comes to
shaving cream formulations. The other
secret to a good lather involves picking
the right fatty acid for the job, because
the length of a fatty acid tail greatly
impacts the texture of the soap. Lauric
acid here has only 12 carbons which is
short by shaving cream standards. Because
the tail is so short, its hydrophilic
head has more influence over the
molecule, allowing it to hold on to water
better. This creates a generous lather
and tons of tiny bubbles. But the problem
is these bubbles aren't structurally
sound on their own, so shaving cream
manufacturers may add in some longer
chain fatty acids to help the bubbles
survive longer on the job. Here is an
example. Stearic acid has a whopping 18
carbons, making it much longer than
lauric acid. That extra length gives the
hydrophobic tail far more influence over
the molecules head, making it much less
soluble in water. It's this insolubility
that adds stability to the bubbles. Now
if we take stearic acid and combine it
with triethanolamine, we get a
particular flavor of soap called
triethanolamine stearate. This is a popular
ingredient in many shaving creams. The
stearic acid helps the bubbles keep
their structure, while the triethanolamine
gives you the copious bubbles necessary
to cover your face, and helps give you
that perfect shave. But we're forgetting the
most important innovation that makes the
soapy mixture into a magical foam:
pressure. Inside a can of shaving cream
our soapy ingredients are packaged under
pressure together with the propellant
such as isobutane. When you press the
button, you release the pressure causing
the propellant to expand. That expansion
causes the contents to woosh up the straw
and out of the can. But the gaseous
propellant is also the source of bubbles!
So as the soapy goo escapes its
pressurized prison, it also becomes a
bubbly foam. Thanks for filling us in, Ms.
Beautyphile. There's a couple of other
things going on in many shaving foam
formulations too. They may contain skin
softeners like glycerol which help make
up for the effects of some of the
harsher soap molecules, and often there
are added fragrances depending on the
manufacturers whims. You know we love us
some chemistry here at Reactions but you
don't have to be a chem PhD to
understand the science behind cosmetics.
Head over to Ms. Beautyphile on Facebook
or YouTube if you want to learn more.
Thanks for tuning in. If you find any
other household products that you want
us to dig into, post your questions down
in the comments and we'll try to get
back to you. Don't forget to hit thumbs
up and subscribe on the way out, and
we'll see you again soon.
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