Skin microbiome

Main

The skin microbiome is the collection of trillions of microorganisms, including bacteria, fungi, and viruses, that reside on the surface and in the deeper layers of human skin. The majority are harmless or beneficial, with around 1,000 different bacterial species from 19 phyla. Most inhabit the superficial epidermis and upper parts of hair follicles. These microbes are generally commensal (not harmful) or mutualistic (offering benefits to the host). They can prevent colonization by pathogens, compete for nutrients, secrete antimicrobial compounds, and stimulate the skin's immune defenses. However, dysbiosis (imbalance) in the skin microbiome composition has been linked to various skin disorders.

The four main types of skin microbiota are:

1. Bacteria: The most abundant and diverse, with key genera including Staphylococcus, Corynebacterium, Cutibacterium, and Streptococcus. For example, Staphylococcus epidermidis is a common commensal that can help prevent colonization by pathogenic bacteria.

2. Fungi: Mainly consist of yeasts from the Malassezia genus. Malassezia globosa and restricta are prevalent commensals that help break down sebum, but can become pathogenic in certain conditions.

3. Viruses: Primarily bacteriophages that infect and replicate within bacteria. They may help regulate bacterial populations and transfer genes between microbes.

4. Archaea: Recently discovered and less well-characterized. Examples include Methanobrevibacter and Nitrososphaera species.

Terms

• Skin flora: The microorganisms residing on the skin, also called skin microbiota.

• Skin microbiota: The microbial communities on the skin, also referred to as skin flora.

• Commensal: Microbes that are not harmful to their host.

• Mutualistic: Microbes that provide benefits to their host.

• Dysbiosis: An imbalance in the composition of the microbiome linked to disease states.

Analogy

The skin microbiome is like a diverse city on the surface of our skin. The city contains different neighborhoods (habitats like oily, dry, or moist skin) where various citizens (microbes) live and work together to protect the city and keep it functioning properly. Just as a city relies on the cooperation of its inhabitants, our skin health depends on the balance and interactions of the microbes living on it.

Misconception

A common misconception is that all bacteria and other microbes on the skin are harmful "germs" that should be eliminated. In reality, the vast majority are neutral or beneficial, and only rarely do certain species or strains become pathogenic. Over-sanitizing the skin can actually be detrimental by disrupting the natural balance of the microbiome and allowing opportunistic pathogens to overgrow.

History

1. Ancient times: Skin microbes have co-evolved with humans for millennia.

2. 1683: Antonie van Leeuwenhoek first observes skin microbes under the microscope.

3. 1950s-1970s: Culture-based studies begin to characterize skin bacterial isolates.

4. 2000s: Modern genomic and metagenomic techniques revolutionize the study of the skin microbiome, revealing its immense diversity.

5. 2010s-present: Research expands to elucidate the roles of the skin microbiome in health and disease, and to develop microbiome-based therapies.

How to Use It

1. Avoid over-sanitizing the skin with harsh antimicrobial products, which can disrupt the natural balance of the skin microbiome. Instead, use gentle cleansers and moisturizers that support the skin's natural barrier function.

2. Moisturize the skin regularly to maintain its integrity and prevent excessive dryness, which can lead to imbalances in the microbiome. Choose moisturizers with ingredients like ceramides, hyaluronic acid, and glycerin that help retain moisture and support the skin barrier.

3. Consider using topical probiotics or prebiotics designed to support a healthy skin microbiome. Probiotics are beneficial microbes that can help restore balance, while prebiotics are ingredients that selectively promote the growth of beneficial microbes already present on the skin.

Facts

• A single square centimeter of skin can contain up to 1 billion microorganisms.

• The skin microbiome begins colonizing at birth and becomes more stable and adult-like by around age 3.

• Certain skin sites, like the glans penis and eyelids, have not yet been well characterized in terms of their microbial diversity.

• Some commensal skin bacteria produce antimicrobial peptides that help protect against pathogens.

• Transplanting a healthy skin microbiome is being explored as a potential therapy for inflammatory skin disorders like atopic dermatitis and psoriasis.