The epidermis is a keratinised, stratified, squamous epithelium. Its thickness ranges from 0.5 to 3mm. depending on its location. Being the most external layer of the skin, it is certainly an important place for microbial invasion.

The most common cell of the epidermis (constituting about 90% of all the cells of the skin) is the keratinocyte. New keratinocytes are constantly being produced in the stratum basale. When they are moved towards the surface, they undergo a process known as keratinization.

This involves the synthesis of a special protein called keratin, and the subsequent death of the cell. The dead keratinized cells (known as squames) populate the outer layers of the epidermis with lipids that fill the intercellular spaces and are slowly sloughed off - a process termed desquamation. It has been calculated that the skin surface of the average adult is composed of about 2 x 10 (9) squames. It takes between 2 and 4 weeks for the passage of a cell from the basal layer to the outermost layer of the skin, and as a consequence of this mechanism, it has been calculated that the stratum corneum is completely renewed every 15 days.

The keratin contained by cells protects the underlying tissues against heat, chemicals, and microbes. Melanocytes are the second most common cells of the epidermis. These have long thin projections that secrete a brown-black pigment termed melanin. This pigment is then moved to the keratonicytes where it blocks ultraviolet light, thus protecting the skin against its harmful effects, and preventing further actinic keratosis symptoms. The only other cells observed in the epidermis are Langerhans cells (which are part of the defensive reaction to microbial intruders) and Merkel cells (which are associated with sensitive neurons and are involved in the sense of touch).

Your skin and the production of acne

The dermis has an extremely complex structure that consists of:

1) Connective tissue containing collagen and elastin fibers conferring the skin elasticity; 2) Tiny finger-like projections (papillae) which reach into the epidermis and have nerve endings sensitive to touch, heat and pain; 3) Hair follicles; 4) Arrector pili muscles for controlling hair movement; 5) Sebaceous glands; 6) Sudoriferous glands; 7) Nerves; 8) Adipose tissue; and 9) Capillaries and veins.

It is essential to know how and why acne issues occur within your skin's anatomy. On the keratin invested follicle canal, where the sebaceous glands reside, Proprionibacterium bactaria exists in symbiosis, feeding on and changing the sebum produced by the sebocytes cells before it submerges on the surface of the skin. The nascent sebum is largely lipid in structure and also contains DNA, RNA, proteins, and other cell components that result from the rupture of sebocytes themselves. Proprionibacterium acne is observed only in sebaceous rich areas.

If the substrates in the follicular canals increase due to an active and large sebaceous system and sebum doesn't flow properly out of the ducts, then colonization and high reproduction rates of Proprionibacterium acne will appear. The resident microbial flora produces biologically active molecules such as histamine, extracellular enzymes and peptides, which can initiate the inflammatory response that characterizes acne breakouts.