Plant-derived system boosts hydration and lipid barrier

A certain balance between skin surface lipids and the water content in the skin layers below provides for a water concentration gradient which is necessary for a healthy and functional skin. An even distribution of moisture to the SC is necessary to allow enzymatic activity and to provide skin elasticity and flexibility.² This distribution of moisture happens from the inner to the outer layers of the skin, which means that the process of skin hydration is not about water being absorbed from the outside but about water being transferred from the inside.³ The skin barrier therefore provides protection in two directions, one against environmental factors and, in the other direction, against an uncontrolled loss of water.⁴ In more than 50 years of research in the field of corneobiology the ‘bricks and mortar’ model has been established to describe the skin barrier and the water holding capacity of the SC.⁵ The three main mechanisms of this model are the cornified envelope, the intercellular lamellar lipid bilayer and the presence of natural moisturising factors (NMF).⁶ As the skin is a constantly growing organ, the skin barrier is also under both constant breakdown and renewal. It starts with the development of the cornified envelope in the stratum spinosum and ends with the desquamation process in the outermost layer of the skin. 

A disruption in any of these processes can cause an impairment of the skin barrier, which will lead to dry skin. Dry skin appears reddened, rough and scaly. People so affected describe their skin to be aching, irritated and itchy. They also experience feelings of tension. The development of dry skin has been described in a cyclical model where a disruption of the skin barrier, whether extrinsically (environmental influences like temperature, humidity or exposure to surfactants) or intrinsically (chronological ageing and genetics) induced, causes a loss of skin moisture and NMF. It will also lead to the inactivation of enzymes involved in the desquamation process. These circumstances trigger an inflammatory hyperproliferative state, which causes the production of poor quality cell material and structures and ultimately a further weakening of the skin lipid barrier and additional loss of moisture. 

To regain skin moisture, it is important not to only treat the symptoms of dry skin, but to repair and augment the skin barrier in order to break the dry skin cycle.⁶ Moisturising creams and lotions fight dry skin by creating occlusive oil, or polysaccharide layers, or delivering NMF such as urea, glycerol or other polyols. Following water, glycerol is the second most widely used raw material in the cosmetic industry. It shows excellent solubility in polar solvents, has numerous skin care benefits, and due to its GRAS status, is very safe to use.⁷ Endogenous glycerol maintains the hydration properties of the SC and thus the barrier function and it has been proven that topically applied glycerol is a very potent humidifying agent.⁸ This is why it is reasonable to include glycerol as a benchmark in testing the efficacy of newly developed moisturising actives.