Water is a great solvent. It’s neutral and doesn’t provide any strong positive or negative effects. It just helps components to mix better and to transport active components.
Decyl glucoside is a surfactant. It provides degreasing and wetting effects. It removes dirt and sebum gently. It doesn’t irritate the skin but at the same time, it’s an effective cleanser. It’s considered to be the safest among all the other surfactants.
Cocamidopropyl Betaine is a pH 4.5-5.5 liquid that is used to improve the overall efficiency of the formulation. It’s usually combined with different surfactants and is used because of its cleansing efficiency. It helps to remove sebum and dirt from the skin and hair. It also works as a foaming agent helping to make a pleasant foam.
Butylene Glycol is a very popular synthetic alcohol. It helps the product to absorb deeper and faster. It is also a solvent for other ingredients. As for the skin benefits, it helps to attract water and helps to make the skin softer.
Unlike many other “Glycols”, it is not harmful and that's why it is used in many products. It was approved by US FDA and US EPA for usage.