A decade ago, I gave my senior expert talk at the University of California, San Francisco, department of dermatology on skin care and brought up the controversial topic that sterile or clean skin is bad. At the time, I initiated the conversation on theToday, I not only preach this message to my patients, but I also practice the “less-is-more” philosophy every day. It is my hope that this brief summary of the skin microbiome and the importance of skin bacteria will affect the development of the next generation of skin care products.
The normal human skin is a microbiome colonized by 10,000-1,000,000 bacteria units/cm2 that prevent the growth of pathogenic organisms and maintain the immunity of the skin. The diversity and type of skin bacteria (that is, Staphylococcus or Propionibacterium acnes), as well as their concentration, varies by person, body location, and environment. Symbiotic with bacteria on the skin are yeasts, such as Malassezia, and parasites, such as Demodex. When the composition and diversity of microorganisms are disrupted, the skin can no longer protect its barrier functions, leading to pathogenic bacterial infections, altered skin pH, decreased production of antimicrobial peptides, and increased inflammation. The microbiome also serves to shield the skin from environmental stressors, such as free radicals, UV radiation, and pollution.
What can lead to disruption of our skin is hygiene. Over-washing; stripping of the skin with lathering cleaner; overexfoliation; long, hot showers; and the use of products with antibacterial properties have increased over the last 50 years, and so has skin disease. The removal of these microorganisms, either by overcleansing or with antibiotic use, disrupts the microflora and leads to pH-imbalanced and inflamed skin. Our microflora contains prebiotics, probiotics, and postbiotics. Prebiotics are the “fertilizer” or “food,” so to speak, that encourages these essential microorganisms to grow; probiotics are the microorganisms themselves; and postbiotics are the chemical byproducts of bacteria, such as antimicrobial peptides and fragments of dead bacterial cells that remain on the skin.
Skin care tailored to our unique microbiome is in its infancy. On the frontier of microflora-rich skin care are organisms like Bifidobacterium longum, which increases the skin’s resistance to temperature and product-related irritation. Streptococcus thermophilus has been shown to increase the production of ceramides in the skin, which could help atopic dermatitis. Lactobacillus paracasei has been shown to inhibit the neuropeptide substance P, which increases inflammation and oil production. Enterococcus faecalis, Streptococcus salivarius, and Lactobacillus plantarum have all been shown to decrease Propionibacterium acnes. Bacillus coagulans and Bifidobacterium breve have been shown to decrease free radicals and protect against UV rays.
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