The skin is one of the most amazing organs of the body. The average adult has about 25 square feet of skin weighing only about seven pounds. It forms the barrier between our tissues and the environment we live in. It makes us waterproof, and it contains nerve endings that allow us to detect hot and cold, as well as even the texture of surfaces touched. Probably the most important aspect of the skin is that it provides a fantastic barrier to infectious agents. We are constantly bombarded with microbes from our surroundings, and our skin keeps these agents from infecting the deeper, sensitive parts of our body. This protection primarily results from the very special architecture of the skin that provides a physical barrier to particles the size of microbes.
Skin architecture
The outer portion of our skin is called the epidermis and is composed of five layers. The outermost layer of the epidermis is called the stratum corneum. It is also known as the horny layer. It consists of about 15 layers, and each is composed of flat dead cells held together by keratin and lipids. The protection provided by these layers is perhaps best understood by considering the cells as bricks and the keratin/lipids as the mortar. Thus, microbes "perceive" the outer portion of our body as several layers of brick walls, which are impossible to penetrate when intact.
The outer layers of the stratum corneum are continually worn off through contact with clothing, taking showers/baths, handwashing, and rubbing with a washcloth or towel. New cells generated from beneath the epidermis replace layers at the rate of about one new layer every day. Thus, all 15 layers may be replaced about every two weeks. As the outermost layers are worn away so are the associated microorganisms. This is good because it keeps microbial accumulation on our skin at a minimum. On the other hand, as we lose the outer epidermis layers, we are constantly shedding microbes into our environment, which may contaminate others.
The skin also has chemically related antimicrobial properties provided by the presence of fatty acids and its normally acidic pH.
Hand hygiene
Hand-washing does a very good job in removing transient microbes from our skin. These microbes are acquired from touching surfaces and have the greatest potential to cause diseases that are spread by the hands. In contrast, the normal flora present on the hands and skin are never completely removed - even with surgical scrub techniques. However, these microbes are not commonly involved in disease spread by the hands, but they still must be part of the barrier offered with gloves in order to avoid direct contact with sterile tissues.
Hand hygiene among all health-care workers is still of primary importance in disease prevention. Hand-washing should occur:
- At the beginning and end of the workday
- Before and after gloving
- Before eating or serving food
- Before applying make-up
- After restroom activities
- At other times after contamination.
Unfortunately, frequent hand-washing can be irritating to the skin. Such irritation can result in less effective hand-washing and greater retention of transient microbes. The irritation also poses a greater risk of hand infection. Thus, some "happy medium" between the frequency of hand-washing and skin irritation must be achieved.
Recommendations to improve the skin health of health-care workers have recently appeared. For example, Emerging Infectious Diseases offered the following in an article titled, "Hygiene of the skin: When is clean too clean?"(http://www.cdc.gov/ncidod/eid/vol7no2/larson.htm).
- For damaged skin, mild, nonantimicrobial skin cleansing products may be used to remove dirt and debris. If antimicrobial action is needed, a waterless alcohol-based product may be used.
- In clinical areas such as an operating room, less traumatic washing regimens may be used instead of lengthy scrub protocols with brushes or other harsh mechanical action.
- Effective emollients or barrier creams may be used in skin-care regimens.
- Skin moisturizing products should be carefully assessed for compatibility with any topical antimicrobial products being used and for physiologic effects on the skin (for example, an anionic surfactant may interfere with the chlorhexidine present in a handwashing product).
In summary, the skin is a fantastic barrier against infection, but if its integrity is lost through injury, microbes may penetrate to deeper sensitive tissues. Hand irritation can result in less effective hand-washing and increased chances of spreading microbes.
Chris Miller, PhD, is professor of oral microbiology and executive associate dean at the Indiana University School of Dentistry.
