HYGIENE
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Postbiotics for hair and scalp microbiome balance
Guglielmo Bifulco, Giorgio Tosti, Francesco Rastrelli, Gianbattista Rastrelli - Kalichem
Recent research has discovered the deep connection between microbiota and human skin. The skin is an ecosystem where about 1,000 microbe species live in symbiosis with each other and with the host. Symbiotic microbes support skin barrier function, modulate immune response protecting the skin against pathogens, allergens and so on. Since the skin is a finely organized
ecosystem, a perfect balance between host and microbe communities exists to preserve homeostasis and wellness. Disruption of this delicate balance can induce perturbations in skin barrier function, onset of dermatological and scalp disorders. Skin microbiota interacts with keratinocytes and the immune system, thus inducing beneficial responses in the host. The scalp microbiota shows some
similarities with the skin microbiota, but possesses unique characteristics. Indeed, the scalp surface provides specific environmental conditions to the microorganisms, depending by moisture, pH, sebum content and other typical physiological conditions of the host.1,2 The hair follicles (HFs), directly connected
to the sebaceous glands through the dermis, represent unique hydrophobic niches which selectively allow the growth of specific microorganisms.3 The exchanges between the scalp surface and the microbiota allow biofilm formation in commensal or pathogenic form,4
i.e. a dysbiosis
in the scalp microbiota was observed in the case of dandruff, similarly as reported for skin microbiota in the case of seborrheic and atopic dermatitis.5-8 A microbial dysbiosis has been also
identified on the scalp of subject affected by hair growth disorders.9
Dandruff is generally
recognized as a mild type of seborrheic dermatitis affecting the scalp. Unbalance of the scalp microbiota, with an increase in Staphylococcus spp. and a reduction in Cutibacterium spp., has been identified as a potential trigger in dandruff formation.
Inflammation and microbiome role in hair disorders Androgenetic alopecia (AGA) is a hair growth disorder featuring the miniaturisation of hair and shortening of the anagen phase, caused by an increased androgen activity. The miniaturisation process is accompanied by micro-inflammation in the HF, as suggested by lymphocyte infiltration, presence of activated
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T-cells and degranulation of mast cells. Micro- inflammation can be triggered by UV radiations, micro-organisms biofilm, IL-6 and androgen activity.11 Micro-inflammation takes place mainly in the upper part of HF, where many microorganisms are present. Many patients affected by androgenetic alopecia, show also seborrheic scalp dermatitis, associated with inflammatory processes, dysbiosis featuring increased growth of S. aureus and decreased colonisation by commensals such as Cutibacterium and Corynebacterium. Proteases, antigens and toxins produced by S. aureus amplify inflammation and induce skin barrier function alterations. Inflammation is also involved in ageing of
the hair. The scalp, as the skin, is subjected to intrinsic and extrinsic ageing. Oxidative stress plays a major role in hair ageing. Outcomes in hair ageing are reduction in melanocyte function, associated with hair greying, and decrease in hair regeneration, causing alopecia. Free radicals may damage melanocytes
in hair bulb inducing hair graying and induce apoptosis in hair follicle cells, thus accelerating
the onset of the catagen phase, followed by hair loss. Keratinocytes react to oxidative stress by
releasing IL-1a, a proinflammatory cytokine able to inhibit the growth of isolated HFs in vitro. IL-1 stimulate adjacent keratinocytes to express TNF-a, IL-1a and the chemokines IL-8 and monocyte chemoattractant protein-1 (MCP-1) and -3 (MCP-3), which allow the recruitment of neutrophils and macrophages in the follicle, thus enhancing the inflammatory response. Prevention of oxidative stress and inflammation could therefore represent an innovative approach to counteract hair graying, hair weakness and alopecia. Scalp microbiota interacts with host keratinocytes and innate immune system producing beneficial effects on HFs and hair mediated by the activity of antimicrobial peptides (bacteriocins), biosurfactants and free fatty acids. The use of topically applied probiotics
could therefore represents a targeted approach to hair and scalp disorders. Many studies reported indeed the health-promoting efficacy of probiotics on skin health.
October 2022 PERSONAL CARE
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