I’m a dude without sisters so that means I grew up with the 30-in-1 shampoo combo. The internet has told me so many times that the combo is bad so I got separate shampoo/conditioner/body wash bottles. But I didn’t know why and that's how this post was born.
Soap/Body Wash vs Shampoo
Shampoos and body wash are both surfactants which cause the suds to build up and “catch” the dirt by reducing the surface tension between the water and the greasy matter on the hair, making it easier to remove dirt. Soap is just stronger than shampoo. Soap would just clean too much and take off the sebum which is the outer protective layer of hair which may cause the hair to become brittle.
Shampoo vs Conditioner
Shampoo gets rid of stuff in/on your hair including the natural oils that are protecting the hair and scalp. Conditioners replace those oils by coating the hair with a protective material such as silicone. Silicone particles stick to your hair via static electricity so that it doesn’t wash out when you rinse.
2-in-1 Shampoo Conditioner combo
The 2-in-1 bad combo is not necessarily bad. The biggest issue is that every person has a unique ideal shampoo-conditioner ratio. There's a reason why ketchup-mustard combos are not popular. Another issue is that washing your hair is a process. First you get rid of the dirt with the shampoo; THEN you replace the protective oils with conditioner. The combo compromises so it does an average job on both. If you’re traveling, a 2-in-1 combo is pretty good since it's compact, but it shouldn’t be an everyday thing.
Chemistry
Surfactants have both hydrophilic and lipophilic segments. The hydrophilic portion is usually a polar group that ionizes in solution to yield charged species. The lipophilic position usually contains a hydrocarbon which is usually 12 carbon atoms in length which I guess is the ideal balance between mildness and dirt removal. Soap has a pH of 9-10 and shampoo has a pH of 6-7 which is means soap is very basic and shampoo is just a little acidic (water is neutral at pH 7).
4 groups of surfactants
Anionics:
Negative charge when ionized
Provide a lot of the lather and detergency.
Cationics:
Positive charge when ionized
Mostly used in conditioners.
Cling to hair by static attraction
Nonionics:
No charge
Good degreasing but provide little foam.
Solubilize fragrances and other oily materials.
Amphoterics:
Zwitterionic
Used in baby shampoos
Very mild, but provide less foam.
Positive charge in acid,
Negative charge in alkaline
FDA requirements
Traditional soaps are a combination of fats/oils + an alkali (usually lye). Most soaps today are made of synthetic detergents because they make suds easier and don’t form nasty deposits. The FDA doesn’t really have any definitions for shampoo or conditioner, but there are 3 conditions for the regulatory definition of soap
Content: Mainly of the “alkali salts of fatty acids,”
Active ingredients: The “alkali salts of fatty acids” must be the only material that results in the cleaning action*
Intended use: Must be labeled and marketed only for use as soap.
Cosmetic: intended for moisturizing, scent, or deodorizing
Drug: treat or prevent disease, but still can be labeled “soap”.
*If the product contains synthetic detergents, it’s a cosmetic, but still can be labeled “soap”.
*No definitions for natural or organic. The same requirements apply no matter whether the ingredients are plant, animal, mineral, or synthetic.
