Our skin contains many layers including epidermis 表皮, dermis真皮 and subcutaneous 皮下tissue. It is a complex ecosystem. By knowing the skin in and out, we can help enhancing the balance with the system.
What we see and touch is the upper layer know as the epidermis 表皮. It is only about 1mm thin yet it is a many-layered structure.
Creating these layers are keratin 角蛋白 producing cells known as keratinocytes 角質形成細胞 with up to 100 layers of these cell forming the epidermis.
How many layers do the epidermis have? Five.
The deepest layers, Stratum Basale, is the site of keratinocyte production. Stem cells there divide to replicate themselves. All the keratinocytes created there will eventually work their way up through all the other layers, right to the top.
The whole process, from stem cell replication to loss from the surface of the skin typically takes about 1 month.
On the skin, there are trillions of microboes which can be beneficial to us.
Beneath the epidermis lies the dermis which is made up with Fibroblasts 纖維細胞, cells which produces collagen and elastin彈性蛋白, as well as the extracellular matrix which surrounds these protein molecules.
The dermis also contains several specialised structures. They are hair follicles, sweat glands, sebaceous glands 皮脂腺體 and sensory receptors.
In skincare perspective, we would like to talk more about sebaceous glands which produce sebum, the oil secretion分沁. It contributes to the skin waterproof and moisturises the skin. Sebum contains acids and that's why the skin's pH sits within the mildly acidic range. This acidity acts as the first defence against bacteria. So it is important to consider the pH of the skincare products as not to knock the pH off the balance.
Blood and lymphatic 淋巴 vessels also run through the dermis, so skincare products may impact these vessels as well.
Beneath the dermis is a layer rich in fat cells and elastin that serves to support as underlaying structures.
As we age, it starts to take longer than a month for those keratinocytes move up to the top, and the epidermis also becomes thinner. Within the dermis, fibroblasts reduce their synthesis of collagen and elastin. We are losing 1% of the collagen from our dermis annually.
With age, our skin also begins to dry due to a reduction in sebum production. Meanwhile, our aging blood vessels become more fragile and less able to nourish the skin. All this results in a thinner, slacker, wrinkled, less plump and dry skin.