The epidermis is a hardened, layered, squamous epithelium. Its thickness ranges from 0.5 to 3mm. depending on its location. Being the most external layer of the skin, it is obviously an important site 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 pushed towards the surface, they undergo a process known as keratinization.

This involves the synthesis of a special protein known as keratin, and the subsequent death of the cell. The dead 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 calculated 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 transfer of a cell from the basal layer to the external layer of the skin, and as a consequence of this process, it has been calculated that the stratum corneum is entirely renewed every 2 weeks.

The keratin contained by cells defends the underlying tissues against heat, chemicals, and microbes. Melanocytes are the second most typical cells of the epidermis. These have long thin projections that produce a dark pigment called melanin. This pigment is then moved to the keratonicytes where it absorbs ultraviolet rays, thus defending the skin against its damaging effects, stopping the development of further actinic keratosis symptoms. The only other cells observed in the epidermis are Langerhans cells (which are involved in the defensive reaction to microbial invaders) and Merkel cells (which are linked with sensory neurons and are involved in the sense of touch).

Getting to know skin anatomy

The dermis has a highly complex structure that consists of:

1) Connective tissue including collagen and elastin fibers giving the skin elasticity; 2) Small finger-like projections (papillae) which protrude into the epidermis and contain 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.

Being aware of the bodily process behind acne problems is important in the search for solutions. On the keratin invested follicle canal, where the sebaceous glands are found, Proprionibacterium bactaria live 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 breakdown 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 evacuate adequately out of the canals, then colonization and high growth rates of Proprionibacterium acne will form. The resident microbial flora creates biologically active molecules such as histamine, extracellular enzymes and peptides, which may trigger the inflammatory response that characterizes acne breakouts.