The scalp, despite being an often-neglected area of beauty and personal care, is essential for our health and wellbeing. The condition of the scalp determines the state of the skin in this area as well as our hair, with a healthy environment preventing irritation and disease and promoting optimal hair growth. However, as well as the scalp itself, it is also important to consider the scalp microbiome.
The role of the microbiome in scalp health, and the importance of keeping it balanced, was first recognized by a study investigating the hair follicles of the scalp area in the 1960s. The research identified that, “In the soil the densest populations of microorganisms are in the rhizosphere, the region that surrounds plant roots. The comparable region in the skin is the hair follicle” [1].
Over years of research, it has come to light that the scalp microbiome has a unique composition of bacteria and yeast which are integral to its health and function. In this blog, we take a look at scalp microbiome composition and how its dynamics influence the skin and hair, taking its role in dandruff as a key example.
Scalp microbiome composition
The scalp microbiome is generally less diverse relative to other areas of the body, which tend to have a bigger mix of microbial residents. It is dominated by two key types of bacterial species – Cutibacterium acnes and Staphylococcus epidermidis – both of which are normal residents of healthy skin but can have negative consequences under certain conditions [2].
Malassezia, a type of yeast, is another key resident of our scalp microbiome. Malassezia are attracted to our scalp as its sebaceous glands, which are present in high concentrations around our hair follicles, produce high levels of lipids that act as a source of food for the yeast. There are many different kinds of Malassezia yeast, but two key species that reside on our scalp are known as Malassezia restricta and Malassezia globosa – each of which are found in varying abundances in populations from different countries [3].
The role of the scalp microbiome in scalp and hair health
Research investigating scalp microbiome composition matters, as it can inform on important aspects of our health. As well as providing the first line of defense against harmful pathogens, these key microbial residents also play a defining role in the maintenance of healthy skin as well as hair growth. This is put at risk when an imbalance – also known as microbial dysbiosis – occurs due to the dense environment of the scalp microbiome and competition between its microbial residents [4,5,6].
Signs of an unbalanced scalp microbiome include flaking skin, itching and irritation. When severe, microbial imbalances can also lead to scalp skin disorders, such as dandruff, seborrheic dermatitis and tinea capitis – all of which have been shown to be associated with altered bacterial and fungal scalp composition [4,7].
Another under-researched field in the microbiome world is the impact of skin microbes on hair growth. The physical proximity of certain microbes to the hair root and associated glands suggests that these microorganisms may potentially influence hair growth, balding and sebaceous lipid production, potentially leading to inhibition of growth and dry, brittle strands, with microbial dysbiosis also shown to contribute to conditions such as androgenetic alopecia [8].
As for the direct cause of the scalp and hair conditions that can arise, Malassezia yeast have been widely implicated [4]. However, a causative link between the yeast and development of such conditions has not yet been established, and more recent work has suggested that it may be an overall microbial imbalance rather than the direct effect of Malassezia or any other individual microbial resident. Here we will explore this in more detail, using dandruff to illustrate.
The role of the scalp microbiome in dandruff
Dandruff is a skin condition affecting the scalp of up to half of the world’s population [9]. The condition is characterized by an itchy and flaky scalp and can cause significant psychological distress. Dandruff is generally associated with colonization of the skin by Malassezia and it often develops during puberty when a hormonal-driven increase in sebaceous lipid production occurs, providing additional fuel for the yeast [10].
Now, for the science behind the link. It has been a running theory that Malassezia yeast secrete several fat-digesting enzymes onto the skin of its host, which break up the lipids secreted by our sebaceous glands to release ‘free’ fatty acids [11]. Only some of these fatty acids will be consumed by Malassezia. The unconsumed fatty acids are left behind and are thought to increase proliferation of keratinocytes – a type of skin cell located in the upper layers of our skin – and consequently cause dandruff-like flaking of human scalp skin [12] (7).
Malassezia yeast also produce additional inflammatory compounds while processing the sebum-derived lipids they use as food [13,14], further worsening the skin’s condition. Certain species have also demonstrated toxicity to skin cells, again suggesting an active role in the acceleration of dandruff [15].
However, more recently, research has suggested that Malassezia yeast alone are not the direct cause of dandruff. Instead, it has been proposed that the association between the yeast and dandruff could instead be an indication of microbial dysbiosis and that it is this overall imbalance that should be defined as the cause.
In support of this view, the yeasts M. restricta and M. globosa, as well as the bacteria C. acnes and S. epidermidis, have all been shown to be present in high abundance in normal, healthy scalps [16]. Also suggesting that the cause of dandruff is not Malassezia or any other microbial resident alone, an increased M. restricta:M. globosa ratio and a reduction in the Cutibacterium:Staphylococcus ratio has been found in the setting of dandruff [16], as well as increased abundance of S. epidermidis bacteria on scalps suffering from dandruff [3] – highlighting again that it is rather a complex interplay between different members of the skin microbiome, rather than single species, that causes scalp conditions.
So, although Malassezia has been shown previously in several publications to be associated with dandruff, these controversial research findings highlight that the causative link between Malassezia and dandruff is missing and that other pathways are also involved.
Gaining a better understanding of these scalp microbiome dynamics is key, as this will have knock-on effects for management and treatment. In the case of dandruff, management is typically via antifungal therapies [17]. However, as the precise roles of microbes in the aggravation of the condition are incompletely characterized, this may not be optimal. Although a reduction of the symptoms has been seen in alignment with a decrease in the proportion of Malassezia species on the scalp when using antifungal treatments, the improvement is usually observed when treatment is stopped, with the relapse restoring the initial symptoms – which may correlate with restoration of scalp microbiome balance.
Managing the scalp microbiome to prevent and treat scalp conditions
Although antifungal treatments may not be optimal for scalp conditions as the dynamics at play are still not fully understood, day-to-day management can help support the scalp microbiome.
One interesting area of beauty and personal care is the repurposing of common skin ingredients that can also help support the scalp and hair. Alpha-hydroxy acids (AHAs) and beta-hydroxy acids (BHAs), chemical exfoliants used often in skincare, can help clarify the scalp from product build-up, excess oil, dead skin and environmental irritants (such as pollen, dirt, pollutants), creating a healthier and more stable environment for the scalp microbiome [18,19]. Hyaluronic acid, which has been rising in popularity due to its benefits in facial care, has also been shown to preserve moisture levels and hydration on the scalp, combatting dry and irritated skin and helping inflammatory conditions associated with an imbalanced scalp [20].
Natural and gentle ingredients with antifungal properties, such as coconut oil, neem oil and tea tree oil, can also help support the scalp and maintain a healthy balance of bacteria and yeast when included in shampoos and other products, with these products shown to decrease dandruff and other symptoms of scalp infection [21].
Coconut oil and its formulations, for example, are commonly applied on the scalp in several parts of the world, including Asia and Africa, to support scalp health. In a recent study investigating the effect of coconut oil on the scalp microbiome, treatment with the oil increased the abundance of C. acnes and M. globosa. This is not surprising, as both species are lipophilic, which means that the fatty oil can be used by the microbes as a source of fuel. However, unexpectedly, the proportional increase of C. acnes and M. globosa was negatively correlated to dandruff parameters [22].
This work provides novel insights on the effect of coconut oil in maintaining a healthy scalp and in modulating the scalp microbiome. Such research also again suggests that it is the relative proportions and balance of microbes that influence scalp health and disease, rather than individual species, laying the way for future research into these dynamics and similar treatment approaches.
Explore more microbiome basics in the How it works section of the Content Hub and follow us on Instagram for the latest updates!
References
1. Marples MJ. Life on the human skin. Scientific American. 1969;220(1):108-15.
2. Grimshaw SG, Smith AM, Arnold DS, Xu E, Hoptroff M, Murphy B. The diversity and abundance of fungi and bacteria on the healthy and dandruff affected human scalp. PloS one. 2019;14(12):e0225796.
3. Soares, R. C. et al. Malassezia Intra-Specific Diversity and Potentially New Species in the Skin Microbiota from Brazilian Healthy Subjects and Seborrheic Dermatitis Patients. PLoS One. 2015; 10(2): e0117921.
4. Gupta AK, Batra R, Bluhm R, Boekhout T, Dawson TL, Jr. Skin diseases associated with <em>Malassezia</em> species. Journal of the American Academy of Dermatology. 2004;51(5):785-98.
5. Polak-Witka, K. et al. The role of the microbiome in scalp hair follicle biology and disease. Exp. Dermatol. 2020 Mar;29(3):286-294.
6. Constantinou, A. et al. The Potential Relevance of the Microbiome to Hair Physiology and Regeneration: The Emerging Role of Metagenomics. Biomedicines 9, 236 (2021).
7. Tao R, Zhu P, Zhou Y, Li Q, Wan Z, Li R, et al. Altered skin fungal and bacterial community compositions in tinea capitis. Mycoses. 2022;65(8):834-40.
8. Suzuki K, Inoue M, Cho O, Mizutani R, Shimizu Y, Nagahama T, et al. Scalp Microbiome and Sebum Composition in Japanese Male Individuals with and without Androgenetic Alopecia. Microorganisms. 2021;9(10).
9. Manuel, F. et al. A New Postulate on Two Stages of Dandruff: A Clinical Perspective. Int. J. Trich. 2011 Jan-Jun; 3(1): 3–6.
10. Turner, G. A. et al. Stratum corneum dysfunction in dandruff. Int J Cosmet Sci. 2012 Aug; 34(4): 298–306.
11. Xu J, Saunders CW, Hu P, Grant RA, Boekhout T, Kuramae EE, et al. Dandruff-associated <i>Malassezia</i> genomes reveal convergent and divergent virulence traits shared with plant and human fungal pathogens. Proceedings of the National Academy of Sciences. 2007;104(47):18730-5.
12. Dawson TL. Malassezia globosa and restricta: Breakthrough Understanding of the Etiology and Treatment of Dandruff and Seborrheic Dermatitis through Whole-Genome Analysis. Journal of Investigative Dermatology Symposium Proceedings. 2007;12(2):15-9.
13. Jourdain R, Moga A, Vingler P, El Rawadi C, Pouradier F, Souverain L, et al. Exploration of scalp surface lipids reveals squalene peroxide as a potential actor in dandruff condition. Archives of dermatological research. 2016;308(3):153-63.
14. Ambaw YA, Pagac MP, Irudayaswamy AS, Raida M, Bendt AK, Torta FT, et al. Host/Malassezia Interaction: A Quantitative, Non-Invasive Method Profiling Oxylipin Production Associates Human Skin Eicosanoids with Malassezia. Metabolites. 2021;11(10).
15. Donnarumma G, Perfetto B, Paoletti I, Oliviero G, Clavaud C, Del Bufalo A, et al. Analysis of the response of human keratinocytes to Malassezia globosa and restricta strains. Archives of dermatological research. 2014;306(8):763-8.
16. Tao R, Li R, Wang R. Skin microbiome alterations in seborrheic dermatitis and dandruff: A systematic review. Experimental dermatology. 2021;30(10):1546-53.
17. Nenoff, P. et al. Cutaneous Malassezia infections and Malassezia associated dermatoses: An update. Hautarzt 66(6):465-84 (2015).
18. https://www.healthline.com/health/beauty-skin-care/alpha-hydroxy-acid
19. https://www.wellandgood.com/remove-scalp-buildup/
20. Sommatis, S. et al. Biological Efficacy Evaluation of a Non-Cross-Linked Hyaluronic Acid Dermal Filler for Biomedical Application in Inflammatory Scalp Conditions. MDPI htps://doi.org/10.3390/life12010002 (2022).
21. https://www.emedihealth.com/skin-beauty/acne/scalp-acne-treatment
22. Saxena R, Mittal P, Clavaud C, Dhakan DB, Roy N, Breton L, et al. Longitudinal study of the scalp microbiome suggests coconut oil to enrich healthy scalp commensals. Scientific reports. 2021;11(1):7220.
