SOAP VS. DETERGENT -
WHAT’S THE DEAL?
Often
when we read descriptions of pet shampoos in catalogues we see the assertion
“soap-free”. Sometimes we see, “no detergents.” What do these mean?
Before
we get to the answer, let’s take a moment to look at these statements as marketing
tools or techniques. A marketing technique is a device of words or images intended
to produce a favorable impression and a desire to buy. The statement “soap-free”
is intended to convey that soap is a bad ingredient and this product has none.
SOAPS
What’s
so bad about soap? Soap is the simplest surfactant; it is formed by the action
of caustic ash or lye on fats. The first soap was probably accidentally formed
when a cave person tossed some animal fat into the fire and when things cooled
down they found...soap. Today’s soaps are created by the action of a
strong alkali, usually sodium hydroxide (lye) on fats or oils. This basic chemical
reaction is called saponification.
Oils + Lye = Salt (soap) + Glycerin
You will see soaps listing their ingredients as
“coconut oil”, “palm oil” or “olive oil”, etc. Technically, this is not accurate. Even the description “saponified oils of coconut, palm and
olive oils” is not the INCI identification(International Nomenclature of
Cosmetic Ingredients). The
accurate names would be Sodium Cocoate, Sodium Palmate, and Sodium Olivate for
soaps from these oils. Sodium
Tallowate, or soap from beef tallow is still a common ingredient in commercial
soaps.
Soap
has served humans for hundreds, even thousands, of years. Soaps are cheap to
make and are manufactured from renewable resources. They are biodegradable and
don’t pollute rivers.
Sounds
good so far, right? But here’s the
rub (soap joke): soaps have a fatal flaw. Soap has a chemical affinity to the minerals
in water and soil, and will combine to form a hard and sticky precipitate known
as soap “curd” or “soap scum”. This is especially troublesome for hair, as it
does not rinse off and will build up over time. It leaves a troublesome dull
film on the hair. Soap scum also clogs plumbing.
There’s more: Most soaps have a highly alkaline pH of
9.5-10. This is in the same range
as chemical straighteners and permanent wave solutions. This makes soap very harsh on hair,
raising the cuticle and leaving it open and susceptible to moisture loss. This can be very problematic for fine
or thin hair, as well as porous hair.
Porosity can cause cuticle damage and moisture loss from the inner
cortex. To close the hair cuticle
after shampooing with soap, using an acidifying rinse is recommended. This can be as simple as vinegar, ¼ cup
in a pitcher of water, or and acidifying rinse, such as ShowSeason Results
Rinse, that will also improve combability and decrease drying time.
Pictured above is a hair shaft with an
open, rough cuticle, such as might be expected by the use of soap on hair
without a pH correction.
Soap is also very irritating to eyes. Liquid soaps can be pH modified to be less irritating, but soap bars cannot.
Soap is also very irritating to eyes. Liquid soaps can be pH modified to be less irritating, but soap bars cannot.
DETERGENTS
OK,
so much for soap. What is a detergent? Technically, a detergent is any surface
acting agent (surfactant) that cleans. That means that in scientific terms,
soap IS a detergent. But for purposes of clarification, most chemists
distinguish between
soaps
and detergents, in that if it cleans and it is not soap.... ta da.... it is a
detergent.
DETERGENTS
can be derived from some of the same fatty acids as soaps, such as coconut or palm
oil. They undergo a more complex
synthesizing process, called sulfation and sulfonation. Chemically, detergents
are often sulfates or sulfonate salts. Sodium Lauryl Sulfate is a prime
example, found in hundreds of cleansing and personal care products. Fear
mongers who make claims about it causing scary things from birth defects to
cancer have crucified Sodium Lauryl Sulfate (SLS) on the Internet. These claims
have no scientific base.
The
truth is SLS is quite harsh and aggressive; it is an excellent cleanser degreaser,
but it is also responsible for cases of irritation and even eczema, and it can damage
eye tissue. It is our association of detergents as harsh chemical ingredients that
leads the marketing people to utilize the concept of “no detergents.” There
are, however, many less harsh and very mild detergents available to shampoo
formulators. Moreover, the formulation of pet shampoos has evolved so that
products that utilize SLS, or Ammonium Lauryl Sulfate or TEA Lauryl Sulfate
combine these aggressive surfactants with co-surfactants such as Lauramide MEA,
Cocomide DEA, and Cocomidopropyl Betaine that lessen the irritation potential
of the strong cleanser without sacrificing cleaning ability.
ETHOXYLATED
DETERGENTS
Some
surfactants undergo an additional process, called “ethoxylation” where they are
treated with ethylene oxide to form larger molecules. This makes the detergent less
harsh without interfering with the cleaning ability. Ethoxylated surfactants
can be recognized by their names. They contain the suffix “…eth”, as in Sodium
Laureth Sulfate, or “PEG” as in PEG-80 Sorbitan Laurate. Some manufacturers use these ethoxylated
detergents as less harsh alternatives to the lauryl sulfates, such as Sodium Lauryl
Sulfate or Ammonium Lauryl Sulfate. The ethoxylates are less likely to cause
shampoo irritation.
The
cosmetic fear mongers have a heyday with ethoxylated surfactants. During the
process of ethoxylation, a potent carcinogen, 1,4 dioxane is released. It is a
very undesirable by-product of a beneficial process. Early in the history of ethoxylated
ingredients, it was discovered that many final products were contaminated with
1.4 dioxane at significant levels. YIKES, shampoos that can cause cancer!!!
This prompted a fear campaign that has not let up, even though most chemical
suppliers have instituted rigorous vacuum stripping techniques to remove the
1.4-dioxane before the ingredient is distributed to shampoo manufacturers.
Another
distinction amongst detergents is between “synthetic” and “naturally derived”
detergent surfactants. Surfactants can be made from petrochemicals or oleo chemicals
(oils, fats). For marketing purposes, those derived from oleo chemicals have been
labeled “natural” and those from petroleum as “synthetic”. The truth is that
both are treated chemically to synthesize into surfactant molecules and the
difference in the resulting carbon chains derived from petro or oleo chemicals
is very slight. They are all synthetic.
A
product that is labeled “no detergent” might be a soap-based shampoo, in which
case it would leave a residue, or more likely, the company is redefining “detergent”
to suit their own marketing. Most often they mean “no ethoxylated detergent”.
Sometimes they mean “no petroleum derived detergent”. Remember, detergency is a property. It
is the ability of a surfactant to clean.
If a product has no detergency, it cannot clean. It does no good to argue with a sales
rep about the definition of a detergent (been there/done that). The way to get
to the bottom of the conversation is to ask, politely, “What is your primary
surfactant?” You can expect it to be a chemical compound.
MILDER DETERGENTS
There
are hundreds of available detergent surfactants for use in personal care and
cleaning products. Some formulating chemists will go to great lengths to find
the most obscure and least used, in order to allow the product in which it is
used to be marketed as containing “no this”, “no that”, “nothing you’ve seen
before.” Of course with pet products, it hardly matters, because they don’t
have to show us what’s in there anyway. A current trend is away from sulfate
surfactants and substitution with detergents that previously were mostly used
in ultra mild, baby shampoos, such as Sodium Cocoamphoacetate and Decyl
Glucoside. The downside of these
very mild detergents is that they do not clean as well, and can’t be diluted
nearly as well as the sulfates.
They are often formulated with two or three together, sometimes with a
little Sodium Laureth Sulfate slipped in to add cleaning power. Remember, less detergency means more
mildness but less cleaning ability.
Of the cleaning surfactants available,
shampoos must contain either soaps or detergent surfactants.
In addition to owning TRANSFORMATION PET CENTER in Tucson, Arizona, BARBARA BIRD is author of the book Beyond Suds & Scent - Understanding Pet Shampoos & Conditioners. She is also half of The Groom Pod, a weekly podcast for groomers. The Groom Pod can be found on iTunes, Stitcher, Facebook or www.thegroompod.com.
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