Introduction

It has been estimated that about 5% of the population suffer from a chronic skin, hair or nail condition; it is also estimated that over half of individuals over 65 years of age suffer from skin conditions such as seborrheic dermatitis, fungal infections and neoplastic growths such as skin cancers. The skin is a remarkable organ, subjected to the extremes of the external environment and altered by the internal environment (the physiological processes occurring within the body), but responding with amazing resiliency.

The Skin

The skin is the largest organ in the body.  Averaging about 1 to 2 mm in thickness with the thickest skin on the palms and soles and the thinnest on the eyelids and scrotum. The skin is the envelope that wraps our body, keeps all the pieces together and serves numerous functions. It may be light or dark, smooth or wrinkled, but it helps define how we appear to others. This body covering, the skin is composed of the epidermis, dermis and the hypodermis.

The Epidermis

The epidermis (0.075 to 0.15 mm thick) is composed mostly of compact, avascular stratified squamous epithelial cells. There are actually five layers to the epidermis (from the innermost to the exterior); the stratum germinativum, stratum spinosum, stratum granulosum, stratum corneum and the stratum lucidum. The lowest layer, the basal cell layer (stratum germinativum) is where new cells (keratinocytes) divide and move upward. The keratinocytes change from living cells to dead, thick-walled, flat, non-nucleated cells containing keratin as they move towards the skin surface. This layer is especially important in laying down new granulation tissue in conditions such as wounds, ulcers, etc. The next layer, the stratum spinosum contains keratinocytes, melanocytes and melanin granules, important for skin pigmentation. Changes in this region can alter skin colouring. Next the stratum granulosum, containing several thicknesses of flattened polygonal cells, are rich in keratohyalin. The stratum lucidum, a translucent, thin area (in the palms and soles) is a narrow band of flattened, closely packed cells. The surface layer, the stratum corneum, is composed of flat, scaly, dead (keratinised) tissue normally exposed to the environment.

The stratum corneum cells are constantly being shed (desquamated) and are replaced by new cells generated by the mitotic process deeper down in the basal cell layer. Actually, the newer cells push the older cells closer to the surface and the cells become flattened, lose water and are compressed as they move towards the surface. From basal cell formation to desquamation, the complete cycle, ranges from 28 to 45 days. The stratum corneum is about 15-20 cells thick; therefore, approximately half to one cell layer per day is sloughed off the body.

The stratum corneum, where most inflammations and disorders occur, maintains its flexibility because of its water content, which is normally between 10 and 20%. This flexibility is influenced by humidity, temperature, surfactants, and physical or chemical trauma. The keratin can actually absorb several times its weight in water and retain it to maintain the flexibility and integrity. Water is important to the skin. Oleaginous (oily) vehicles such as the paraffins are occlusive and aid in retaining the moisture in the skin. The stratum corneum is primarily lipophilic.

Dermis

The dermis (about 1 to 4 mm thick), or basement membrane separates the epidermis from the lower fatty layers and actually physically supports the epidermis. The dermis is composed mainly of collagen and elastin embedded in a mucopolysaccharide substance, containing fibroblasts and mast cells. The dermis also contains a network of nerves, lymphatic and blood vessels, supplying hair follicles, sebaceous glands and sweat glands. It is this layer where the cutaneous sensations occur, for example, itching from the upper region, stinging from the middle region and pain in the region closest to the subcutaneous fat. The dermis contains the papillary and reticular layers. The former is rich in blood vessels and appears to aid in bringing nutrients to the avascular epidermis. The lower portion, the papillae, contains coarser tissue that connects the der­mis with the hypodermis. Altered pain perception can occur when this layer is damaged, or destroyed.

Hypodermis

The subcutaneous tissue, called the hypodermis is composed of loose connective tissue and adipose tissue. This layer aids in thermal control, holds nutrients and provides cushioning and/or padding. Burns extending into this area require close monitoring of the patient, depending upon the extent of involvement.

PURPOSE OF THE SKIN

The skin, the largest organ in the body, is the protective barrier between the body and the environment. The skin works to protect the body from chemicals and pathogenic organisms; its functions are dependent upon, and in association with, age, immunologic status, underlying disease states, use of oral/topical medications and the preservation of an intact stratum corneum.

In addition to protection. the skin also serves for temperature control, pigment development, water regulation/moisture loss and even vitamin synthesis.

The skin can be challenged by wounds, burns, chafing. drying. internal physiological disorders. chemicals and bacteria. resulting in alterations and may involve the different skin layers. Commonly encountered dermatologic disorders include general classes of dermatitis and dermatoses. Specifically, allergic skin diseases include urticaria, atopic dermatitis (eczema), allergic contact dermatitis and photoallergic reactions. Others include insect bites/stings, acne, burns (including sunburn), minor wounds, skin infections, cancers, skin ulcers, hyperpigmentation, photoaging, lice infestation and even hair loss.