Mannitol is a sugar alcohol. It is a humectant and moisturizes the skin. In vitro (not tested on a living organism), mannitol displays antioxidant properties.

When found in aqueous solutions, mannitol tends to become acidic. This is because it loses a hydrogen ion. This is why mannitol can often be found with pH adjusting ingredients, such as sodium bicarbonate.

This ingredient is derived from caprylic and capric acids. It is an emulsifier with emollient properties.

According to the manufacturer, it is hydrophilic and soluble in aqueous solutions (water). They also state this ingredient is stable in a medium pH range (~5 - 8).

Propylene Glycol is an odorless, colorless liquid. As a humectant, it helps skin retain moisture. It also aids in delivering active ingredients.

Another role of this ingredient is preventing a product from melting or freezing. Propylene glycol also adds antimicrobrial properties to a product, elongating product lifespan.

Water. It's the most common cosmetic ingredient of all. You'll usually see it at the top of ingredient lists, meaning that it makes up the largest part of the product.

So why is it so popular? Water most often acts as a solvent - this means that it helps dissolve other ingredients into the formulation.

Xylitol is a humectant and prebiotic. It can help with dry skin.

In studies, xylitol has been shown to improve dry skin. It decreased transepidermal water loss, or when water passes through the skin and evaporates. Xylitol also showed to help improve the biomechanical properties of the skin barrier.