The Effect of Handwashing on Skin Flora

The skin, the largest organ of the body, is made up of several layers of living and dead cells. The living layers include the connective tissue layers called the hypodermis and the dermis with a rich supply of blood and lymph as well as sensory receptors, sweat glands, sebaceous glands and hair follicles.
Also alive are the lower layers of the epidermis (the stratum basale, stratum spinosum, stratum granulosum and the stratum lucidum) the squamous epithelial cells of which are constantly dividing and synthesizing keratin.

Once keratinized, these cells undergo APOPTOSIS or "programmed cell death" to form the outer surface layer of the epidermis (the stratum corneum); a surface layer composed of multiple layers of dead, keratinized squamous epithelial cells.

The skin's surface is typically a dry environment although perspiration and sebum serve to moisten the skin with a cocktail of salts, lipids, lysozyme and other proteins in water. These secretions are inhibitory to many microorganisms but they are also nutritive and growth promoting for many of the NORMAL FLORA organisms. These normal flora tend to be resistant to drying and tolerant of high salt concentrations. These organisms are highly adapted to this environment, hanging on tenaciously, colonizing the deep layers and spaces between the cells of the stratum corneum as well as the many hair follicles, sebaceous gland ducts and sweat gland pores. Vigorous washing may briefly reduce their numbers but the population will rebound quickly.

The normal skin flora serves some useful purposes. Most notably many of these organisms produce organic acids such as proprionic acid which lowers the pH and makes the skin less hospitable to many of the more harmful TRANSIENT FLORA. Perhaps another beneficial effect of the normal flora would be the production of volatile, aromatic compounds which each of us come to recognize as our own natural scent.

The common skin organisms include: Staphylococcus epidermidis, Staphylococcus aureus, Corynebacterium xerosis and Proprionibacterium acnes.

Numerous studies have shown that handwashing by health care practitioners helps to reduce the spread of infection within the hospital and clinic environment thereby reducing the incidence of NOSOCOMIAL infections (1-5).

In spite of these studies and in spite of the fact that there are many good handwashing agents available; it is often difficult to establish rigorous handwashing habits even by people who have been highly trained and should know better. Overall, routine handwashing before, during and after general patient care occurs in approximately half of the instances in which it is indicated and usually is of shorter duration than recommended. Additionally, hospital staff generally overestimate the frequency and quality of their handwashing behavior (6).

Washing with detergent or plain soap is usually sufficient for the removal of transient flora although repeated handwashings may be necessary if the hands are exceptionally soiled or if contamination has been rubbed in. On the other hand, washing with soap and water has been reported to increase the amount of shedding of normal flora organisms (7,8). (Keep this in mind when interpreting the results of our experiment.)

The purpose of the surgical hand scrub is to not only remove and destroy any transient flora but also to reduce the resident normal flora. A variety of antimicrobial soaps and lotions are used to achieve this in conjunction with vigorous handwashing and brushing. The most common antimicrobial ingredients include:

• ALCOHOLS
  Ethyl and isopropyl alcohols are among the safest antiseptics. They have excellent antibacterial, antiviral and antifungal activity when used at concentrations between 70 - 90%. Alcohols are active against Mycobacterium tuberculosis but they are not active against endospores. The antimicrobial activity is not neutralized by blood. It is necessary to use a sufficient quantity of alcohol and the skin must be thoroughly wetted to achieve good antisepsis. Alcohols are not good cleaning agents, therefore the hands should first be washed with soap and water if there is significant physical dirt present.
• IODINE and IODOPHORS
  Iodophors are complexes of iodine and a carrier such as polyvinylpyrrolidone (povidone). These complexes increase the solubility of iodine and also provide a reservoir of iodine. Iodine and iodophors are good antiseptics with antibacterial, sporicidal, tuberculocidal, antiviral and antifungal activity. However these antiseptics are easily inactivated by organic matter such as blood and sputum and this is a major limitation. Also, iodine antiseptics tend to irritate the skin and may trigger allergic reactions in sensitive people.
• CLORHEXIDINE GLUCONATE
  This agent is usually offered as 2-4% detergent formulations and foams. Alcohol based hand rinses are also available. This agent has good antibacterial and anti-enveloped virus activity, but it has minimal activity against M. tuberculosis and no activity against endospores. This agent is important because it has a very strong residual or persistant effect. After a few days of daily use, skin bacterial counts become as low or lower as that after an alcohol wash. This agent is non toxic when used on skin and it is not neutralized by organic material. There are reports that it is pH sensitive and that it can be neutralized by substances in hand creams and natural soaps. Therefore the effectiveness of this agent may differ between individuals (9, 10).
• TRICLOSAN
  This agent is commonly used in soaps to control body odor. It has good antibacterial activity and poor antifungal activity. There is no conclusive information about its antiviral activity. It has good persistant activity on the skin and may help reduce colonization with methicillin resistant Staphylococcus aureus

REFERENCES:

1. Steere, A.C. and Mallison, G.F., Ann Intern Med, 1975; 83:683
2. Garner, J.S. and Favero, M.S., Infect Control, 1986; 7:231
3. Khan, M.U., Trans R Soc Trop Med Hyg, 1982; 76:164
4. Black, R.E., et. al., Am J Epidemiol, 1981; 113:445
5. Ansari, S.A.,et. al., J Clin Microbiol, 1991; 29:2115
6. Larson, E.L., Am J Infect Control, 1994; 22:25A
7. Lilly, et. al., J Clin Pathol, 1979; 32:382
8. Larson, E., et. al., Infect Control, 1986; 7:59
9. Babb, J.R., et. al., J Hosp Infect, 1991; 18 (Suppl B):41
10. Nicoletti, G., et. al., J Hosp Infect 1990; 15:323
11. Webster, J., J Hosp Infect 1992; 21:137