The epidermis is a hardened, stratified, squamous epithelium. Its density 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 colonization.

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

This implies the synthesis of a unique protein called keratin, and the eventual death of the cell. The devitalized keratinized cells (known as squames) comprise the outer layers of the epidermis with lipids that fill the intercellular spaces and are gradually sloughed off - a process termed desquamation. It has been estimated that the skin surface of the average adult is made of approximately 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 result of this process, it has been estimated that the stratum corneum is completely renewed every 2 weeks.

The keratin present in cells protects the underlying tissues from heat, chemicals, and microbes. Melanocytes are the next most common cells of the epidermis. These have long slender projections that produce a brown-black pigment called melanin. This pigment is then moved to the keratonicytes where it blocks ultraviolet light, thus protecting the skin from 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 immune reaction to microbial invaders) and Merkel cells (which are associated with sensory neurons and are involved in the sense of touch).

Know your skin's anatomy

The dermis has a highly complex structure that consists of:

1) Connective tissue containing collagen and elastin fibers giving the skin elasticity; 2) Small 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 are found, Proprionibacterium bactaria exists in symbiosis, feasting on and changing the sebum secreted from the sebocytes cells before it submerges on the exterior of the skin. The nascent sebum is largely lipid in structure and also contains DNA, RNA, proteins, and other cellular components that result from the rupture of sebocytes themselves. Proprionibacterium acne is observed only in sebaceous rich areas.

If the nutrients in the follicular canals increase due to an active and large sebaceous system and sebum doesn't evacuate adequately out of the canals, then colonization and high reproduction rates of Proprionibacterium acne will appear. The resident bacterial flora creates biologically active molecules such as histamine, extracellular enzymes and peptides, which may initiate the inflammatory reaction that characterizes acne breakouts.