Skin Barrier Properties and Effect of Hand Hygiene Practices

The average adult has a skin area of about 1.75 m² . The superficial part of the skin, the epidermis, has five layers. The stratum corneum, the outermost layer, is composed of flattened dead cells (corneocytes or squames) attached to each other to form a tough, horny layer of keratin mixed with several lipids, which help maintain the hydration, pliability, and barrier effectiveness of the skin. This horny layer has been compared to a wall of bricks (corneocytes) and mortar (lipids) and serves as the primary protective barrier. Approximately 15 layers make up the stratum corneum, which is completely replaced every 2 weeks; a new layer is formed approximately daily. From healthy skin, approximately 10⁷ particles are disseminated into the air each day, and 10% of these skin squames contain viable bacteria. The dispersal of organisms is greater in males than in females and varies between persons using the same hygienic regimen by as much as fivefold.

Water content, humidity, pH, intracellular lipids, and rates of shedding help retain the protective barrier properties of the skin. When the barrier is compromised (e.g., by hand hygiene practices such as scrubbing), skin dryness, irritation, cracking, and other problems may result. Although the palmar surface of the hand has twice as many cell layers and the cells are >30 times thicker than on the rest of the skin, palms are quite permeable to water.

Long-term changes in skin pH associated with handwashing may pose a concern since some of the antibacterial characteristics of skin are associated with its normally acidic pH. In one report, pH increased 0.6 to 1.8 units after handwashing with plain soap for 1 to 2 min and then gradually declined to baseline levels over a period of 45 min to 2 hr. Some soaps can be associated with long-standing changes in skin pH, reduction in fatty acids, and subsequent changes in resident flora such as propionibacter.

In an investigation of the effect on skin of repeated use of two washing agents, all skin function tests (stratum corneum capacitative resistance, lipids, transepidermal water loss, pH, laser Doppler flow, and skin reddening) were markedly changed after a single wash, and after 1 week further damage was noted. In a study of irritant skin reactions induced by three surfactants, damage lasted for several days; complete skin repair was not achieved for 17 days.

Soaps and detergents have been described as the most damaging of all substances routinely applied to skin. Anionic and cationic detergents are more harmful than nonionic detergents, and increased concentrations of surfactant result in more rapid, severe damage. Each time the skin is washed, it undergoes profound changes, most of them transient. However, among persons in occupations such as health care in which frequent handwashing is required, long-term changes in the skin can result in chronic damage, irritant contact dermatitis and eczema, and concomitant changes in flora.

Irritant contact dermatitis, which is associated with frequent handwashing, is an occupational risks for health-care professionals, with a prevalence of 10% to 45%. The prevalence of damaged skin on the hands of 410 nurses was reported to be 25.9% in one survey, with 85.6% of nurses reported to have problems at some time. Skin damage was correlated with frequency of glove use and handwashing. Washing with plain soap may actually increase the potential for microbial transmission because of a 17-fold increase in the dispersal of bacterial colonies from the skin of the hands. Skin condition clearly plays a major role in risk for transmission.

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Dr. Larson is professor of pharmaceutical and therapeutic research, The School of Nursing, and professor of epidemiology, Mailman School of Public Health, Columbia University. She is editor of the American Journal of Infection Control and former chair of the Healthcare Infection Control Practices Advisory Committee (HICPAC) and member of CDC's National Center for Infectious Diseases Board of Scientific Counselors. Address for correspondence: Elaine Larson, Columbia University School of Nursing, 630 W. 168th St., New York, NY 10032, USA; fax: 212-305-0722; e-mail: ell23@columbia.edu

The source of this article is http://www.cdc.gov