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

The most common cell of the epidermis (comprising about 90% of all the cells of the skin) is the keratinocyte. Fresh keratinocytes are continually being produced in the stratum basale. As they are moved towards the surface, they undergo a process called keratinization.

This implies the production of a unique protein known as keratin, and the subsequent death of the cell. The devitalized keratinized cells (called squames) comprise the outer layers of the epidermis with lipids that occupy the intercellular spaces and are slowly sloughed off - a process termed desquamation. It has been estimated that the skin surface of the average adult is composed of about 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 process, it has been estimated that the stratum corneum is completely renewed every 15 days.

The keratin present in cells defends the underlying tissues against heat, chemicals, and microbes. Melanocytes are the next most common cells of the epidermis. These have long slender projections that produce a dark pigment called melanin. This pigment is then moved to the keratonicytes where it absorbs ultraviolet light, thus defending the skin against its damaging 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 sensitive 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 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.

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 live 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 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 augment due to an active and large sebaceous system and sebum doesn't flow properly out of the canals, then colonization and high growth rates of Proprionibacterium acne will form. The resident bacterial flora produces biologically active molecules like histamine, extracellular enzymes and peptides, which can trigger the inflammatory response that characterizes acne breakouts.