top of page

It is the superficial layer of the skin,  consisting of keratinocytes, which are by far the most abundant cells in the body , arranged in overlapping layers. Primary function  of the epidermis is to place a barrier between the organism  and environment  external.

The basal layer, the deepest, rests on the  dermis , located under the epidermis. The subsequent layers (Malpighian and grainy) contain more and more  keratin , the  protein  characteristic of the epidermis, up to the stratum corneum, superficial, which is extremely rich in it; the cells  death  they are eliminated through a process of  peeling .

The epidermis also contains melanocytes and Langerhans cells and is traversed by structures from the  dermis , such as the ducts of the sweat glands and hair follicles; the latter comprise the root of the hair and act as excretory ducts for the sebaceous glands. The orifices of glands and follicles are said  pores.

Keratinocytes have a very peculiar life cycle: they appear following the division of one  cell  of the basal layer of the epidermis, with the passage of time they move towards the surface, secreting and accumulating  keratin , and when they die they dissolve in the stratum corneum. There  keratin  surface flakes off in very thin flakes to give way to the one that forms in the underlying part.

The epidermis, waterproof, resistant and at the same time elastic, increases the  power  skin protective. There  keratin  protection against water  and physical and chemical aggression, Langerhans cells against injuries that threaten immunity  mobile phone.


Low molecular mass lipophilic molecules enter the stratum corneum essentially through the intercellular pathway , ie between the corneocytes and through the intercellular lipids. The higher the concentration of skin lipids in the bilayers, the slower the penetration rate of the hydrophilic molecules. By increasing the fluidity of skin lipids, penetration is facilitated.

In the intracellular pathway, the molecule passes through the lipid membranes and the cytoplasm of the corneocytes in the stratum corneum. This path is difficult to cross because it must first pass through the lipophilic membrane of each cell, then the hydrophilic center of the cell, and then re-enter through the lipophilic membrane. This therefore tells us that a molecule must have both hydrophilic and lipophilic characteristics to be able to follow this path of penetration. Molecules with hydrophilic and lipophilic character are called anphilic.

The intrafollicular path allows penetration through the hair follicles, which represent 1-2% of the total skin surface. The intrafollicular pathway is used in particular by large molecules, which are generally highly insoluble.  In addition, the pilosebaceous follicles tend to eliminate lipophilic substances and the flow of sebum.  As for electrolytes, the intrafollicular pathway is the only pathway to the skin.

In conclusion, cosmetic products can ...

Distribute across the top of the skin and potentially penetrate the stratum corneum (the outer layer of the skin) a little. This provides hydration to the skin and helps reduce water loss, helping to improve the overall appearance of the skin.  

Penetrate beyond the upper layer of the skin to the central part of the epidermis (granular layer). For example, humectants can do this. When they do, they will draw water from the environment and deeper layers of the skin to give you more supple looking skin. As a result, the active ingredients are often combined with humectants (e.g. glycerin, butylene glycol) to attract them into the granular layer.

Penetrate into the deeper layers of the epidermis (basal layer).  For example, some substances such as peptides, which can stimulate skin changes, such as collagen synthesis. To achieve this level of penetration, the active ingredients are often put into an emulsion base combined with a humectant and / or some sort of delivery agent.

Penetrate into the dermis
Considering all the parameters and variables, we can understand what will be functional on our skin and what will remain on the surface!

bottom of page