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The effect of antibacterials on the skin


The microbiome is one of the most popular areas of skin research at present. Many dermatologic diseases are accompanied by abnormal microbiomes beginning with atopic dermatitis, says Dr. Zoe Diana Draelos in her monthly column, Cosmetic Conundrums.

Q. What is the skin microbiome?

Dr. DraelosThe microbiome is composed of all of the organisms that live on the skin’s surface. Believe it or not, there are over 1,000 species of bacteria on the skin’s surface with a distribution of one million microorganisms per square centimeter. The most common species are from the Actinobacteria, Firmicutes, Proteobacteria, and Bacteriodetes families. Fungi, such as Malassezia species, and mites, such as Demodex species, are also found. There are two types of skin organisms: resident microbes and transient microbes.

Resident microbes are a fixed group of organisms found on skin that re-establish themselves after perturbation, such as cleansing. They are commensal and not pathogenic. Transient microbes are not permanently established microbes that are obtained from environment. They can be harmful if the skin is damaged, but remain nonpathogen with good hygiene.

The microbiome is one of the most popular areas of skin research at present. Many dermatologic diseases are accompanied by abnormal microbiomes. Atopic dermatitis has long been thought to be a skin microbiome disease related to staph aureus, a Firmicutes. Staph aureus, a pathogen, is found in more than 90% of atopic dermatitis patients, who exhibit increased levels of staphepidermidis, a nonpathogen. Staph epidermidis expresses endopeptidase and antimicrobial peptides that interfere with Staph aureus colonization.

Thus, a healthy microbiome is key to the prevention of recurrent disease. Research is currently trying to define a healthy microbiome and provide mechanisms to maintain this organism mix.

Q. Why are antibacterials so controversial?

Antibacterials have become very controversial because by definition they are designed to alter the microbiome. If the microbiome contains abundant MRSA organisms, antibacterials can reduce colonization and prevent disease. However, if the microbiome is healthy and composed of nonpathogenic organisms, the antibacterial can create an unhealthy situation. Unfortunately, antibacterials are indiscriminate killers equally destroying pathogenic and nonpathogenic organisms.

The antibacterial controversy was brought to a head by the FDA who announced in September 2016 that it would prohibit the sale of triclosan and 18 other ingredients marketed as antimicrobials by September 2017. Triclosan (2,4,4’-trichloro-2’-hydroxydiphenyl ether), a chlorinated phenolic compound killing gram negative bacteria through cell membrane damage, was widely used in antibacterial and deodorant bar and liquid cleansers. The FDA removed these products from the market because their antibacterial value was unproven. Industry was charged with proving that antibacterials killed bacteria such that the claim could be validated, yet the skin can never be totally sterilized and bacterial repopulation of the microbiome occurs rapidly in healthy individuals. More research is needed to better under the microbiome before the claim of antibacterial can be vetted.

Most manufacturers of deodorant cleansers now use benzalkonium chloride, an organic salt classified as a quaternary ammonium compound a cationic surfactant, as the antibacterial to kill odor causing body bacteria. However, benzalkonium chloride is also under FDA consideration for banning, except the ban was deferred to allow ongoing studies regarding its topical efficacy to be completed. These studies are proceeding slowly.

Q. Are hand sanitizers good antibacterials?

Hand sanitizers have become increasing popular for medical use prior to patient examination in clinics and hospitals. They are easy to use as water is not required. They can be squeezed and rubbed over the hands without rinsing, eliminating the need for a sink, water, and towels. The most commonly used hand cleansers contain ethanol, which kills both gram positive and gram negative bacteria and fungal organisms.

However, ethanol is not effective against bacterial spores and has variable efficacy in killing enveloped viruses. Ethanol hand sanitizers are flammable and cannot be used where open sparks are present, such as in the operating room around electrocautery equipment.

While hand sanitizers may be important in limiting the spread of contagious disease, they are not eff ective against anthrax and Clostridium difficile. Hand sanitizers are not good at removing visible dirt from the hands and are best used on clean hands that might contain nonvisible dirt. While hand sanitizers can solubilize intercellular lipids, a study in health care workers demonstrated better skin condition with the use of hand sanitizers as opposed to frequent hand washing.


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