by Paolo Giacomoni
Introduction to the Human Microbiome
Our body harbors trillions of micro-organisms. They add up to three to four pounds of bio-material, that is to say about the weight of our brain. New technologies are at hand to identify micro-organisms and to estimate their number in a given sample. Today we know that micro-organisms colonize the guts, the sexual organs and the skin. Micro-organism in our guts participate in the process of digestion and are associated to obesity; micro-organisms in sexual organs can metabolize HIV-preventing drugs and make them ineffective. Micro-organisms colonizing the skin have a variety of effects, as outlined below.
The Formation and Evolution of the Skin Microbiome
The skin microbiome is defined when we are born. Babies born vaginally or via a Cesarean cut have different microbiomes, that are modified during our life by the environment and by our lifestyle. To belong to the cutaneous microbiome, a microorganism must adhere, multiply and invade. Secreted proteases carve a niche in the surface, and biofilms are synthesized to favor adhesion. Skin biochemistry and cutaneous micro-flora find a balance that can be perturbed (1, 2). As a matter of fact, the molecular composition of skin is defined not only by skin cells and microbes but also by our daily routines, including the application of hygiene products.
Key Microorganisms Found on the Skin
In the skin microbiome, we find the well-known Corynebacterium: a micro-organism that is niched in the axillary pits, digests lipids and releases smelling, volatile molecules. We also find Propionibacterium acnes, a pro-inflammatory anaerobic organism associated with acne on the face and with dandruff in the scalp. The scalp is also the niche for the fungus Malassezia furfur and the bacterium Staphylococcus. These microorganisms coexist within the skin ecosystem and contribute to both normal and pathological processes depending on their balance.
Skin Conditions Linked to the Microbiome
Several unwanted skin conditions might be caused by microorganisms. For instance, Atopic Dermatis (A.D.) might be the consequence of modified skin microbiome. A small study with facial swabs pointed out that Stenotrophomonas maltophilia was significantly more common in the 13 A.D. patients tested whereas Dietzia maris was significantly more common in the10 healthy controls (3). These findings suggest that variations in microbial populations may play a role in the development or progression of certain dermatological conditions.
Probiotic Treatments and Their Effects
Probiotic treatments could alleviate pruritus! Forty-four A.D. patients were administered Bifidobacterium animalis subsp lactis or placebo by general route. Pruritus was alleviated in patients receiving probiotic treatment and the anti-pruritus, anti-nociceptive metabolite Kynurenic acid was found in patients with decreased pruritus (4). These results highlight the potential systemic influence of probiotics on skin-related symptoms and the connection between internal microbiota and external skin health.
Topical Treatments for Skin Sensitivity
Topical treatments are effective, too! A topical cream containing a lysate of Bifidobacterium longum sp or a placebo was applied twice a day for two months on volunteers with reactive skin. The volunteers who applied the cream with bacterial extract had a significant decrease in skin sensitivity (5). This demonstrates that targeted topical applications can directly influence the skin microbiome and improve skin conditions locally.
The Role of Cosmetics and Future Perspectives
And what about cosmetics? Microorganisms can provoke pruritus, sensitivity, inflammation, rosacea, malodor, dryness, acne, dandruff, etc. It should be possible to topically apply specific nutrients that favor the growth of beneficial microorganisms so that the harmful ones are outgrown and eliminated. And to fulfill the dream of "beauty from within", it should also be possible to ingest specific prebiotics to associate topical and general "treatments" to improve skin conditions.
Questions and Answers
What is the skin microbiome?
The skin microbiome refers to the community of microorganisms that live on the skin, including bacteria and fungi, which interact with skin cells and influence skin health.
How is the skin microbiome established?
It is defined at birth and differs depending on whether a baby is born vaginally or via Cesarean section, then evolves over time due to environmental and lifestyle factors.
Can microorganisms cause skin problems?
Yes, certain imbalances in the skin microbiome are associated with conditions such as acne, dandruff, and atopic dermatitis.
Are probiotics beneficial for skin health?
Research shows that probiotics can help reduce symptoms like pruritus and may influence skin health through systemic effects.
Do topical products affect the skin microbiome?
Yes, topical treatments containing bacterial extracts can reduce skin sensitivity and positively impact the skin microbiome.
References
(1) Grice EA et al (2008) A diversity profile of the human skin microbiota. Genome Res 18 :1043-1050
(2) Nakatsuji T et al (2013) The microbiome extends to subepidermal compartments of normal skin. Nat Commun. 4 : 1431-1442
(3) Dekio I et al (2007) Characterization of skin microbiota in patients with atopic dermatitis and in normal subjects using 16S rRNA gene-based comprehensive analysis. J Med Microbiol 56 : 1675-1683
(4) Matsumoto M et al (2014) Antipruritic effects of the probiotic strain LKM512 in adults with atopic dermatitis. Ann Allergy Asthma Immunol. 113 : 209-216
(5) Guéniche A. et al (2010) Bifidobacterium longum lysate, a new ingredient for reactive skin. Exp. Dermatol. 19 : 1-8
