Introduction
The skin is composed of three types of tissue: epidermis, dermis and hypodermis.
The epidermis is the most superficial tissue of the skin which is in turn divided into a basal or germinative layer, a thorny layer, a granular layer and a stratum corneum. It is at the level of the granular layer that the cells synthesize lamellar vesicles rich in lipids. Several enzymes transform the phospholipids, once they have escaped from the cells of the granular layer, into ceramides, free fatty acids and cholesterol.
At the level of the stratum corneum these lipids form together with the corneocytes, a barrier defined as "bricks and mortar" which opposes the loss of water from the underlying tissues.
The corneocytes ("the bricks") constitute about 85% of the stratum corneum, and the intercellular lipids ("the mortar", about 15%) are arranged on about 15-20 layers forming a real barrier against the entry of external substances and the escape of vital fluids. A reduction of the barrier function, due to a lower production of interlamellar lipids or to a lower sebaceous secretion, can be the cause of a greater loss of water through the epidermis (increase of TEWL), therefore of dry skin that is characterized by the lack of tone and elasticity, and for the easy tendency to flaking and cracking.
- Cosmetics containing lipids with emollient properties and with a function similar to those present in the stratum corneum (such as ceramides) can improve the altered conditions of the skin as they favor the recovery of the barrier function.
Emolliency and cosmetic ingredients with emollient properties
The term emolliency derives from the Latin "mollis" and means "soften, soften".
- In the dermatological and cosmetic field the word emolliency indicates the set of phenomena that make the skin perceptibly smooth, soft and elastic.
From this it can be seen that oily substances are the emollients par excellence : oils and fats, of vegetable, animal, mineral and synthetic origin - which constitute a class of water insoluble organic compounds, oily to the touch - for their chemical structure they find a great application in dermocosmetic.
From a chemical point of view, the emollients can have a great variability, going from esters to alcohols, but there are also hydrocarbons, acids, triglycerides and waxes.
Natural lipids are made up of complex mixtures with variable composition, such as vegetable or animal oils and butters, consisting of triglycerides, vegetable and animal waxes, whose composition is based on the presence of esters of acids and higher fatty alcohols, mineral oils and waxes ( aliphatic and aromatic hydrocarbons).
Synthetic lipids, on the other hand, have a well-defined chemical composition; they belong to the chemical class of hydrocarbons, esters, triglycerides or alcohols; a significant part of synthetic lipids is represented by silicone derivatives.
For years, due to its low cost and high stability, the most widely used emollient was Vaseline oil, a mineral oil which, applied to the skin, forms a lipid film that prevents the loss of water from the superficial layers reducing their dehydration and helping to keep it smooth and smooth. To date, there is a tendency to prefer the use of vegetable oils, naturally derived or synthetic hydrocarbons of known composition (hydrogenated polydecenes, silicones). These have the advantage of poor occlusion and non-penetration; they can also form protective films and strengthen the skin barrier, thus acting as water supplements in the skin. The skin lubricating effect is one of their characteristics together with the ability to reduce irritation without occlusive effects.
A substance is all the more emollient the more it increases the sensation of softness of the skin after direct application. The way in which this occurs is closely linked to the concept of spreadability and the formation of an oil / fat film that determines the lubrication of the skin surface. The more fatty emollients will spread with more difficulty on the skin determining also a more occlusive effect compared to the less fat substances. This is why the emollient creams are formulated by adding lipid-rich emollients to night creams (which promote occlusion), emollients that are moderately greasy for day creams, more spreadable emollients and more volatile for milks destined to be applied on larger surfaces (legs, arms, etc.). The emollient ingredients can also have nourishing and moisturizing properties.
- By nourishing property is meant the ability of lipids to penetrate between the cells of the epidermal stratum corneum favoring their elasticity, decreasing the presence of scales and making the skin more homogeneous to the touch.
- The moisturizing effect consists in the ingredient's ability to slow down the natural water loss through the most superficial layers of the skin.
Ultimately, the feeling of emolliency is due to two effects; that of lubrication by means of fatty substances and that of hydration through the use of hydrophilic substances.
