I have decided to write a couple of posts about the skin structure because it is very important to understand what goes on at “skin level” if we want to formulate effective and safe cosmetics.
Our skin consists of two main layers (Epidermis and Dermis). Under the Dermis there is a third layer, the Hypodermis (in this picture called “Fatty Tissue”), which is not considered part of the skin organ and it is mainly made of fat cells.
It is very interesting to know that our skin is so well organized: the deepest layer of the Epidermis is the layer where new keratinocytes are formed and with time they go through many of transformations until they reach the Stratum Corneum being eventually shed.
- Stratum Corneum: it is made of flattened dead cells that keep shedding.
- Stradum Lucidum: it is a translucent layer made of densely packed dead cells (we find this layer only in the palm of our hands and the sole of our feet).
- Stratum Granulosum: this is the layer where the keratinocytes begin to die and start flattening.
- Stratum Spinosus: in this layer the cells synthesize proteins and lipids that will be very important for keeping the cells “together” in the following stages and, therefore, the skin protected.
- Stratum Basale: or “basal layer”: it is where the keratinocytes are born. In this layer we also find other kinds of cells: Langerhans cells, Merkel cells and Melanocytes.
In the Stratum Corneum (SC) the cells are in a very particular structure:
they find themselves in a pool of “lipid matter” that makes the layer water-resistant and protects the skin from dehydration. The corneocytes (the dead flat cells in the SC) are covered in a protective mix of proteins and ceramides and they are tightly kept attached to each other by very strong “strings” called corneodesmonosomes (mainly made of proteins and ceramides as well).
Inside of the corneocytes there is a mixture of hygroscopic compounts (aminoacids, minerals, sugars, lactic acid, urea) which are, by definition, compounds that have the ability to attract water and keep it attached to them. These compounds are usually referred to as the Natural Moisturizing Factor (“NMF“) and keep the skin hydrated.
The Dermis supports the Epidermis by supplying it with oxygen and other nutrients in an osmotic mechanism.
In the Dermis we find:
- Extracellular matter: which acts like a cushion and it contains Collagen, Elastin, Glycosaminoglycans (our friend Hyaluronic Acid is one of them),
- Fibroblasts: which produce collagen fibers and extracellular matter,
- Sebaceous Glands: we find them mostly on our face and scalp. They produce sebum, which reaches the surface through pores and lubricates the skin.
- Other components are blood vessels, nerves endings, sweat glands, hair follicles…
It is important to notice that when we formulate a cosmetic, we mostly affect only the Epidermis.
I will write more posts on the subject soon!
Let me know if there are any questions 🙂