The human skin provides a living space for a rich and diverse population of microorganisms collectively known as the skin microbiome. This consists of bacteria, archaea, fungi, viruses and mites, most of which are harmless commensals providing benefits for us. For example, they protect the skin against colonization by pathogens, produce various antimicrobial peptides and influence host innate and adaptive immunity; for a review, see Byrd et al.1 Microbial lipases also hydrolyze sebum triglycerides,2 releasing glycerol and moisturizing the skin;3 and free fatty acids, maintaining the acid mantle, which is important for skin barrier formation and, together with proper skin hydration, for desquamation.4
The most common members of the human skin microbiome are bacteria, with Cutibacterium acnes (formerly Propionibacterium) and Staphylococcus epidermidis being the most abundant species.1 Notably, an imbalance in the skin microbiome is often associated with a wide range of skin diseases such as acne, psoriasis, atopic and seborrheic dermatitis, etc.1
The composition of the human skin microbiome depends on many factors, such as body location, gender, age, diet, hygiene habits, environment and lifestyle. The present study focuses on skin cleansing, which represents one of the most common everyday challenges to the skin microbiome. Moreover, in the context of the recent COVID-19 pandemic, more frequent and thorough skin cleansing with harsher cleaners and disinfectants has become a worldwide standard. Though these simple routines save lives, they also represent a significant threat to the skin, reducing the number of our beneficial skin commensals. For these reasons, cosmetic active ingredients supporting the skin microbiome are coming to the forefront.
Different approaches have been used to support the skin microbiome, including probiotics, prebiotics, postbiotics and synbiotics (see Table 1);5-8 the present work focuses on prebiotics. Historically, most research about prebiotics has focused on gut inhabitants. Gut prebiotics are typically indigestible fibers based on carbohydrates such as galacto- or fructo-oligosaccharides and inulin.9 On the other hand, prebiotics applied to the skin do not need to survive the harsh conditions of the gastrointestinal tract, so they can be less resistant and include a much broader group of compounds.
Many polysaccharides already used as cosmetic actives for moisturizing and/or anti-aging effects could serve as nutritional sources for the skin microbiota and therefore used as skin prebiotics.
The present study evaluated the effects of select cosmetic polysaccharides including hyaluronic acid (HA) of different molecular weights (MW)—i.e.,1.6 MDa, 300 kDa, 16 kDa and 3.6 kDa; carboxymethyl beta-glucan (CM-glucan); glucomannan; and schizophyllan on the growth of bacterial species in vitro using cell cultures, and in vivo on the cleansed skin of human volunteers.
- Byrd, A.L., Belkaid, Y. and Segre, J.A. (2018). The human skin microbiome. Nat Rev Microbiol 16 143–155.
- Ingham, E., Holland, K.T., Gowland, G. and Cunliffe, W.J. (1981). Partial purification and characterization of lipase (EC 22.214.171.124) from Propionibacterium acnes. J Gen Microbiol 124 393–401.
- Fluhr, J.W., Mao-Qiang, M., Brown, B.E., Wertz, P.W., Crumrine, D., Sundberg, J.P., Feingold, K.R., and Elias, P.M. (2003). Glycerol regulates stratum corneum hydration in sebaceous gland deficient (asebia) mice. J Invest Dermatol 120 728–737.
- Harrison-Tryon, et al. (2022, May 27). Microbiota and maintenance of skin barrier function. Science 376 940-945.
- Hill, C., Guarner, F., ... Salminen, S., et al. (2014). Expert consensus document. The International Scientific Association for Probiotics and Prebiotics consensus statement on the scope and appropriate use of the term probiotic. Nat Rev Gastroenterol Hepatol 11 506–514.
- Gibson, G.R., Hutkins, R., ... Cani, P.D., et al. (2017). Expert consensus document: The International Scientific Association for Probiotics and Prebiotics (ISAPP) consensus statement on the definition and scope of prebiotics. Nat Rev Gastroenterol Hepatol 14 491–502.
- Vallianou, N., Stratigou, T., Christodoulatos, G.S., Tsigalou, C. and Dalamaga, M. (2020). Probiotics, prebiotics, synbiotics, postbiotics and obesity: Current evidence, controversies and perspectives. Curr Obes Rep 9 179–192.
- Collado, M.C., Vinderola, G. and Salminen, S. (2019). Postbiotics: Facts and open questions. A position paper on the need for a consensus definition. Benef Microbes 10 711–719.
- Davani-Davari, D., Negahdaripour, M., ... Ghasemi, Y., et al. (2019). Prebiotics: Definition, types, sources, mechanisms and clinical applications. Foods Basel Switz 8.