Even though they look kinda similar, shampoo bars and soap are definitely not the same thing. They’re both for cleaning stuff. But they’re specifically designed to clean different things – hair and skin.
Hair and skin have different pH levels so require cleansers with pH levels to suit. Good shampoos should be around 4.5-5.5 (acidic) and traditional soap is usually over 7 (alkaline) so too ‘harsh’ for hair.
It is good for shampoo to be acidic (though that sounds weird). According to cosmetic scientist Dr Barbara Olioso, acidic shampoos won’t strip your hair and scalp of their natural oils, which are there to protect against dryness, frizz and damage. An acidic shampoo will also seal the hair cuticles which keeps it strong and shiny.
Traditional soaps (aka cold pressed and hot process soaps) and our shampoo bars are also made in two very different ways. Traditional soap is made by mixing an alkali (usually lye) with oil in a chemical reaction known as saponification. Our shampoo bars are made with the same melt-and-mix method as our liquid shampoos. Just without the water and with the addition of mango butter and palm-free stearic acid to harden them.
Technically they are ‘sydnet bars’ rather than soaps. Sydnet is a word made up from ‘synthetic’ and ‘detergent’. The detergent we use (Sodium Cocoyl Isethionate) is a synthetic detergent that is originally derived from coconut oil. It’s very mild so it doesn’t damage the acid mantle or remove protective lipids or oils like a traditional alkali soap would.
Syndet bars perform better in hard water than soap, so still give a lovely lather and rinse out easily if you happen to live in a hard water area (like us).
There’s more about washing your hair with soap in this post by The Beauty Brains.