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Shampoo Bar vs Soap Bar - What Is the Difference?

Updated: May 4, 2019


You look at the soap bar and the shampoo bar- they look almost the same. So, why not use the soap on your hair and on your body?


What is the difference between shampoo bars and soap?

Sometimes you wonder, maybe you should just use the soap bar on your hair as well as your body it would help simplify the shower routine. But would normal soap be harmful to hair? What do they do to shampoo bars that is different?

After all, they are all just different versions of soap, right?


Well…not exactly. Soap bar or liquid soap are designed to wash your body, while shampoo and conditioner are specifically formulated for your hair.

Although shampoo and soap may look, feel, and smell similar and have some common ingredients, there are many differences.

To start, they have very different targets.


Soap, chemically speaking, is a surfactant (a definition of a surfactant reads: “a substance that tends to reduce the surface tension of a liquid in which it is dissolved”) composed of the salt of a fatty acid, typically lauric, palmitic or stearic acids. Soap is produced by adding a strong hydroxide base (Caustic Soda) to liquefied plant or animal fat, which liberates the fatty acids from the triglyceride via hydrolysation, where they then bind with the free cations from the base forming an amalgam of salts.



Both shampoo and soap are act in a similar way; they have a hydrophilic (water-attracting) side, and a hydrophobic (water-repelling) side. When dissolved in water (which happens slowly unless the surfactants are already dissolved), the hydrophobic side is attracted to anything that isn't water, and so it will loosely bind via various forces to mineral compounds and organics such as those found in dirt, grease, oil etc. These molecules end up surrounding small particles of these substances on all sides in a bid to "shelter" their hydrophobic end, forming a "micelle". The hydrophilic side exposed to the water, then, allows the micelle to float away in the water and resists the substance in the core of the micelle reattaching to the surface it had been on (dishes, clothes, skin, hair etc), so it can be easily rinsed away.


Shampoo is similar, but produced by a different process, to create a surfactant that is less likely to bond to the mineral compounds in hard water, and so is more effective than soap when using it with tap water from most regions.

Proper hair care is complicated by the fact that there are many different types of hair with varying compositions. That's why you'll notice the shampoo shelves at your local store has so many different types of shampoo for a wide variety of applications, such as dry hair, oily hair, color-treated hair, etc.

Each special formulation requires unique ingredients to properly treat a specific type of hair. Shampoos also formulated to be delicate, able to cleanse without degreasing, easy to rinse out, and formulated to minimise eye irritation.


Most shampoos have a pH level between pH-5.5 and pH -6,5 which is close to the natural pH level of hair.

Hair reacts both to acids and alkalis. Each hair has little cuticles, like scales on a snake or shingles on a roof. Acid makes the scales lie down flat, which makes your hair shiny and smooth. Alkali on the other hand makes the scales stand up, which makes your hair look dull and feel rough and tangled. And the soap is highly alkaline, it’s pH is over pH-8!



Little bit about the pH.

We often encounter the term “pH balance." Our skin and hair have their own natural pH levels that, if imbalanced, can lead to all sorts of problems.

PH is stands for Potential Hydrogen, It refers to the acid-basic ratio of a substance. The more hydrogen ions available, the more acidic, and the lower the pH.

There is a 0-14 scale denoting if something is alkaline (with high pH) or acidic (low pH). The middle, 7, is neutral, and anything less than that increases in acidity, whereas anything above it increases in alkalinity.

Different elements and organisms carry different natural levels, and a neutral 7 isn’t necessarily equilibrium.


Maintaining healthy pH levels is essential to keeping your skin and hair happy, especially skin of your face. It can help prevent aging and generally keep your face clear of irritation.

It is obligatory that the pH of the cosmetic products remain in a certain range to guarantee consumers' safety. The pH of cosmetic products designed for everyday application must be compatible with the physiological skin pH (which is 4,5-5,5).


Exception is the soap which by nature has a much higher pH (around 9.0-11.0).

This makes the natural soap a little bit controversial. Soap lovers and admirers use it despite the fact that it kicks the pH of their hair and skin out of balance. People using soap instead of shampoo because they think that soap is more natural.

But what is the definition of "natural"? For example, it's highly unlikely that the Lye- Caustic Soda which is used in soap making process is natural. As caustic Soda is synthetically produced.


Commercial soaps claiming a neutral and balanced pH are not real soap. They are NOT made by Saponification of a fat or an oil.( Saponification is a process that involves conversion of fat or oil into soap and alcohol by the action of heat in the presence of aqueous alkali (Caustic Soda, NaOH).

They are blends of surfactants pressed together as a soap bar (or made as a liquid handwash)


There are certain products with a much higher or much lower pH than the physiological range (4,5-5,5). These include chemical peels, hair dyes and hair strengthening products, chemical hair removal products. These are however, no everyday use products and are applied only occasionally and sometimes by a trained hair stylist or aesthetician. Even for these products, the pH should be measured and adjusted to guarantee their stability, safety and performance.


Soap was created long before shampoo. Over time, however, the need for shampoo became clear, because using soap caused hair to become dry, rough, and damaged. Soap simply tends to be too strong for regular use on hair, as it strips away hair's natural protective oils, and lives hair’s cuticles sticking out and open.


If you use soap to wash your hair, then the combination of your hair’s scales standing up and the soap forming scum makes your hair into an awful mess. And, since your hair is all tangled and rough, it’s impossible to rinse out all the soap, which makes everything even more awful.


Your skin is a living organ that regenerates its outer layer on a regular basis. Your hair, on the other hand, is mostly dead material that has grown from live cells that exist below the surface of the skin.


Even if you're tempted to use shampoo on your skin instead of soap, you'll find that it often leaves your skin feeling slimy. Soap or liquid soap is formulated with stronger detergents for your skin, which can often contain more oil and dirt than your hair usually does.

While soap tends to be less specialised than shampoo, soap manufacturers have expanded their product lines to contain products with moisturisers, conditioners, and fragrant scents.

But- it is impossible to make the soap with a low-acidic pH.


Some products may even claim to be an all-in-one combination of shampoo, conditioner, and soap. If you use these products, though, just be aware that they might not be the best product for either your skin or your hair!

In my next blog post i will show you how to choose the right product.


References:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4158629/




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