What actually contributes to the thickness of a product? They are a specific group of ingredients called rheology modifiers or known to most as ‘thickeners’.
Nearly all formulated products will contain rheology modifiers. They can be categorised into 2 groups, depending on what they can thicken.
Oil thickeners thicken the oil component of any lotions/creams (which can exist as cleansers, moisturisers or masks) and waterless-balms. They are typically solid, waxy substances at room temperatures.
Oil thickeners are generally occlusive; they moisturise passively by limiting water loss from skin. Following as some examples; they are all relatively efficient except plant butters which generally require a high concentration (i.e. 10% and above) to thicken significantly.
- Fatty acids: stearic acid, myristic acid, oleic acid
- Fatty alcohols & derivatives: cetearyl alcohol, cetyl alcohol, cetyl palmitate
- Waxes: beeswax, carnauba wax, microcrystalline wax
- Plant butters: shea butter, mango butter, cocoa butter
Water thickeners give body to the water component of any lotions/creams as well as water-only products such as toners, essences, and serums.
They are typically water-soluble powders which absorb a large amount of water after its dissolution, causing the water to gel up and thicken. They are chosen based on the chemical compatibility with the other ingredients in the same formula. Examples are
- Natural gums: xanthan gum, acacia gum, sclerotium gum
- Cellulose derivatives: hydroxyethylcellulose, hydroxypropylcellulose
- Acrylates derivatives: carbomer, acrylates/c10-30 alkyl acrylate crosspolymer
Rheology and variety
Although thickeners do not contribute much to skin benefits (other than occlusivity), they are a vital group of ingredients.
Combining different rheology modifiers will result in a vast range of light to heavy textures. If you are wondering why we need so many different product consistencies, we'll be discussing more of that in the final instalment, so watch this space!