The epidermis is a hardened, layered, squamous epithelium. Its thickness varies from 0.5 to 3mm. depending on its location. Being the most external 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. Fresh keratinocytes are continually being created in the stratum basale. When they are pushed 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) populate the outer layers of the epidermis with lipids that occupy the intercellular spaces and are gradually sloughed off - a process called desquamation. It has been estimated that the skin surface of the average adult is composed 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 external layer of the skin, and as a consequence of this mechanism, 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 second most typical 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 absorbs ultraviolet light, thus defending the skin from 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 immune reaction to microbial intruders) and Merkel cells (which are linked 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) 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 lined 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 reaches the exterior of the skin. The nascent sebum is largely lipid in structure and also has 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 ducts, then colonization and high reproduction rates of Proprionibacterium acne will appear. The resident bacterial flora produces biologically active molecules like histamine, extracellular enzymes and peptides, which may trigger the inflammatory response that characterizes acne breakouts.