Skincare and LPS

(1) Structure of the Skin

The skin consists of three layers: the epidermis, the dermis, and subcutaneous fat (from outside to inside). The epidermis is about 0.2 mm thick. The most common cell present in the epidermis is keratinocyte. Keratinocytes divide at the lowermost epidermis layer and undergo cellular morphological changes as they are pushed upward through the epidermis. As a result, cell groups of different morphologies are piled up on top of one another in the order of (from bottom to top): the basal layer, the spinous layer, the granular layer, and the stratum corneum. The Stratum corneum consists of dead keratinocytes with sebum filling the gaps around them. The dead keratinocytes and sebum serve as an important barrier in the topmost layer of the skin, similar to that of the bricks and mortar of a wall. As the stratum corneum ages and its barrier function degrades, it scales off as “grime”. Replacement of all epidermic cells, called a “turnover”, takes place at a rate of about once every month in healthy skin.

The epidermis also contains Langerhans cells, which closely resemble macrophages, and T cells, which control immunity and inflammation.

In the second granular layer of the epidermis, there is a structure called a “tight junction”, which tightly seals the gap between adjacent cells. Thanks to the “tight junction”, the skin is protected from the invasion of foreign matter from the outside and the evaporation of moisture from the inside. The skin is structured in such a manner that it does not allow molecules to go in or out easily.