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Skin Health Skin Health Basics

Wound Healing and Pressure Sores

Author:

Gregory Buford, MD

Center for Plastic and Aesthetic Surgery, Englewood, CO

Medically Reviewed On: October 24, 2001

Our Outer Layer...the Skin

Before you can understand how a wound heals, you need to first know something about skin. Our skin, perhaps the organ most commonly disregarded, must withstand assault from a daily barrage of factors including sunlight and UV irradiation, wind, temperature extremes, and the daily insult of cuts, nicks, and scrapes, which leave it susceptible to invasion by fungus, bacteria, and viral invaders.

In addition to keeping the harsh external environment away from our own critically sensitive internal biological environments, skin acts as a regulator of body temperature and a sealant against fluid loss. You can appreciate its many roles by looking at its two major layers-the outer epidermis, and the deeper underlying dermis.

Epidermis
The epidermis is continually exposed to the environment and sustains most of the injury to the skin. As a result, it is shed and regenerated on a daily basis. Its major role is to produce the stratum corneum-a waterproof, semi-permeable membrane on the outermost portion of the epidermis that acts to prevent water loss from the tissues it surrounds. When this upper layer is injured-as can occur with minor scrapes and cuts-it simply regenerates itself without scar formation. The same is not true for deeper injuries.

Dermis
Residing just below the epidermis is the dermis, which constitutes 90% of total skin thickness. Because of its rich collagen content, the dermis is the strength layer of the skin. In addition, it contains blood vessels, nerve endings, hair follicles, and immune cells that act as sentries against infection and cancer.

These two layers are draped over a deeper subcutaneous layer comprised of fatty tissue, blood vessels, and nerves which is generally protected from injury by the overlying epidermal and dermal covering.

Wound Healing

Under normal conditions, the process of healing occurs in three overlapping phases. Roughly speaking, these are divided into inflammatory, proliferative, and remodeling phases and involve contraction (downsizing of the wound), epithelialization (creation of new epithelial cells), and deposition of connective tissue.

Inflammation
When skin is injured-whether in a planned injury such as a surgical incision or as the result of trauma-an inflammatory phase begins. This is initiated by the release of several chemicals from both platelets (tiny cells which initiate the clotting mechanism) and the surrounding injured tissue. The site of injury turns red, becomes swollen, and displays all the normal properties we commonly associate with an acute wound.

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