The epidermis is a hardened, stratified, squamous epithelium. Its density varies from 0.5 to 3mm. depending on its location. Being the outermost layer of the skin, it is obviously an important place for microbial invasion.

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

This involves the production of a unique protein known as keratin, and the eventual death of the cell. The devitalized keratinized cells (known as squames) comprise the external layers of the epidermis with lipids that fill the intercellular spaces and are slowly sloughed off - a process called 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 14 and 28 days for the passage of a cell from the basal layer to the outermost layer of the skin, and as a result of this mechanism, it has been estimated that the stratum corneum is completely renewed every 15 days.

The keratin present in cells protects the underlying tissues from heat, chemicals, and microbes. Melanocytes are the second most typical cells of the epidermis. These have long thin projections that produce a brown-black pigment called melanin. This pigment is then moved to the keratonicytes where it blocks ultraviolet light, thus defending the skin from its harmful 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 associated with sensory neurons and are involved in the sensation of touch).

Know your skin's anatomy

The dermis has an extremely intricate structure that consists of:

1) Connective tissue containing collagen and elastin fibers giving the skin elasticity; 2) Small finger-like projections (papillae) which protrude into the epidermis and have nerve endings sensitive to touch, heat and pain; 3) Hair follicles; 4) Arrector pili muscles for coordinating 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 lined follicle canal, where the sebaceous glands are found, Proprionibacterium bactaria exists in symbiosis, feasting on and changing the sebum produced by the sebocytes cells before it reaches the exterior 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 found 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 adequately out of the ducts, then colonization and high reproduction rates of Proprionibacterium acne will form. The resident bacterial flora produces biologically active molecules such as histamine, extracellular enzymes and peptides, which may initiate the inflammatory response that characterizes acne breakouts.