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Page 6 of 10 Abadías-Granado et al. Plast Aesthet Res 2021;8:27 https://dx.doi.org/10.20517/2347-9264.2020.199

Figure 1. External and internal factors that influence the composition of the microbiome.

As research on the skin microbiome progresses, there is growing interest in finding ways to help the skin to
recover and regenerate from the numerous microorganisms living on it. In this sense, the manipulation of
the gut microbiota of older adults could be an innovative strategy in the prevention and treatment of age-
related comorbidities; therefore, a balanced skin microbiota could help to prevent premature skin aging .
[26]
Recently, oral and topical probiotics have been proposed as a therapy for restoration of the microbiota
balance, supporting skin barrier function, as well as protecting against environmental factors, especially
ultraviolet radiation-induced skin damage [36-38] . The following are some examples of relevant effects in the
skin caused by different microorganism: Streptococcus thermophiles enhance ceramide levels of the stratum
corneum when is topically applied on the skin ; and some probiotics help to restore the balance between
[39]
[40]
free radical removal and production, which may slow aging . On the other hand, oral and topical
compounds are being investigated to know their potential therapeutic effect on the modulation of the skin
[41]
microbiome : Orobanche rapum extract stimulates skin rejuvenation and protects the cutaneous
microbiota, inducing healthier skin . In addition, the term “Photobiomics” has recently been introduced,
[42]
referring to the use of low levels of visible or near-infrared light to modify the gut microbiome through
photobiomodulation .
[43]

THE MICROBIOME AND SKIN CANCER
The occurrence of malignancies increases with age. The association between the microbiome and
malignancies is a recent and not very well studied hypothesis also in skin cancer. Different studies suggest
the role of microbiome in the tumoral genesis and/or progression, especially the gastrointestinal one.
Additionally, the gut microbiota seems to play an important role in the response to immunotherapy, and,
perhaps, this could also be extrapolated to the skin microbiota [16,17] .

Some of this work indicates that dysbiosis may promote cancer. In normal circumstances, the microbiome
does not induce a pro-inflammatory response due to the tolerance that the immune system has developed to
commensal bacteria, preserving homeostasis . When these mechanisms are disrupted or new pathogenic
[17]
microorganisms enter into this balanced system, dysbiosis occurs and the immune system is activated
towards the microbiome, causing inflammation [18,44] or modifying the local immune response, which can
trigger the tumoral growth in the intestine [16,17] . It has also been reported that intestinal inflammation
enhances the possibility of the microbiota to produce genotoxins that cause damage to DNA, promoting the
[45]
development of tumors .