The scalp microbiome

While many articles discuss the role of the microbiome in skin conditions, few focus on the scalp microbiome and its implications in certain pathologies. Yet, interest in this field is growing (1).

The unique ecosystem of the scalp:

The scalp has its own microbiome, distinct from that of other skin surfaces due to its specific environmental conditions (2) :  

• High humidity

• Protection from UV rays

• A pH level conducive to microbial growth

The scalp microbiome is essential for maintaining homeostasis and regulating inflammation (3). 

Advances in sequencing have revealed that the scalp harbors a microbiome mainly dominated by commensal bacteria and fungi, the primary ones being (4) :

• Fungi of the genus Malassezia

• Bacteria of the genus Cutibacterium

• Bacteria of the genus Staphylococcus

Microbial balance and dysbiosis:

A healthy scalp is characterized by a balance between the different populations that make up the hair ecosystem. A disruption of this balance, known as dysbiosis, is in some cases associated with the onset of conditions such as:

• Seborrheic dermatitis or excessive dandruff (1,3) 

• Androgenetic alopecia (1,3)

Seborrheic dermatitis is strongly associated with an increase in Malassezia and Staphylococcus populations, correlated with a decrease in Cutibacterium. Lipases secreted, particularly by M. restricta and also C.acnes hydrolyze sebum into triglycerides, which are in turn hydrolyzed into fatty acids, causing impairment of the skin barrier, inflammation, and accelerated desquamation (3).

Androgenetic alopecia is the most common form of hair loss in both men and women, characterized by the gradual miniaturization of hair follicles. Although it is primarily caused by hormonal and genetic factors, some studies suggest that micro-inflammation at the follicular level, potentially exacerbated by dysbiosis, may accelerate hair loss (1).  

The microbiome is a dynamic ecosystem influenced by several factors:

• The host 

• The environment 

• Lifestyle habits 

Our expertise: 

Together, we can measure the impact of your hair care ingredients on the scalp microbiome by offering you tailored preclinical tests. 

• Efficacy testing on synthetic microbiota 

• Development of synthetic microbiota

• Conventional, targeted, or comprehensive microbiological approaches (ex: characterization of the microbiome in clinical samples)

• In vitro measurement of lipase activity 

• Development of an ex vivo model colonized by microbial species 

Bibliography: 

1.         Polak-Witka K, Rudnicka L, Blume-Peytavi U, Vogt A. The role of the microbiome in scalp hair follicle biology and disease. Exp Dermatol. 2020;29(3):286‑94. doi:10.1111/exd.13935

2.         Saxena R, Mittal P, Clavaud C, Dhakan DB, Hegde P, Veeranagaiah MM, et al. Comparison of Healthy and Dandruff Scalp Microbiome Reveals the Role of Commensals in Scalp Health. Front Cell Infect Microbiol. 4 oct 2018;8. doi:10.3389/fcimb.2018.00346

3.         Shah RR, Larrondo J, Dawson T, Mcmichael A. Scalp microbiome: a guide to better understanding scalp diseases and treatments. Arch Dermatol Res. 29 juill 2024;316(8):495. doi:10.1007/s00403-024-03235-2 PubMed PMID: 39073596.

4.         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. 18 déc 2019;14(12):e0225796. doi:10.1371/journal.pone.0225796