Background:
Around half of the adult population worldwide is affected by the condition known as dandruff (Soares et al. 2016). Dandruff is characterized by small white flakes that are shed from the scalp, which often end up in a person’s hair or on their shoulders. Dandruff can cause intense itchiness of the scalp. Having visible dandruff flakes can lead to social embarrassment, due to the stigma that dandruff is caused by poor personal hygiene (e.g., not washing your hair enough). This is not true, however. It is not known what the exact cause of dandruff is, but Malassezia yeasts, specifically an imbalance/overabundance of them, are/have been suspected to play a role in its development (Wang et al. 2015). Malassezia is a fungal genus, and it is normal for fungi belonging to it to live on human skin (Soares et al. 2016), along with other species of fungi and bacteria, like Propionibacterium acnes and Staphylococcus epidermidis (Clavaud et al. 2013). In 2018, researchers in India conducted a study on the scalps of 140 Indian women to learn more about what kinds of microbes (including bacteria and fungi) were present on dandruff scalps vs. healthy scalps (Saxena et al. 2018).
Central Questions:
One of the main questions the authors of the study were asking was “what is the bacterial and fungal diversity of the scalp microbiome?’ A second question they had was “what is the functional role of those microbes in both healthy scalps and scalps with dandruff?’
Evidence:
Saxena et al. (2018) looked at the scalps of 70 Indian women with healthy (i.e., dandruff-free) scalps and 70 Indian women who had dandruff on their scalps. For each person, the researchers assessed the severity of their dandruff and measured the sebum (oil produced by the sebaceous glands in the body) level, trans-epidermal water loss (how much water passes through the outer layer of the skin and evaporates), and hydration level (the water content of the skin) of their scalp. Sebum is important for scalp health because it reduces water loss from the surface of the skin, and protects the skin from infection by microbes. Although sebum level often correlates with dandruff, it is not the definitive cause of it (Borda et al. 2015). Next, the researchers swabbed the scalp of each participant with a sterile cotton swab to collect a sample from them, then sequenced the DNA of the microbes that were present on the swab. Sequencing the DNA allowed the researchers to learn which species of bacteria and fungi were present on subjects’ scalps.
People who had dandruff on their scalp had a higher alpha diversity for the fungal population than those with a healthy scalp. This means that the dandruff scalps had a higher diversity (how evenly the fungal species were distributed) within each dandruff scalp than the healthy scalps had within each healthy scalp. The frequency of the fungal species M. globosa was significantly higher in the healthy scalp. The dandruff scalp was also found to have a significantly higher frequency of uncultured Malassezia species, unknown species of Malassezia, and species that were similar to Malassezia restricta.
Possible Next Steps:
The next step in further exploring this topic is to do similar studies on different populations, to see if the results are similar to those found in this paper. The climate people live in (dry, humid, cold, hot, etc.) could have an impact on what species of microbes are present on human scalps, because different microbes prefer different kinds of environments to live in. People in different countries or parts of the world might wash their hair more or less often than people living in India, or be more or less likely to use antifungal shampoos or take antibiotics for other medical reasons. I would also be interested to see the same study done on men, to see if there are any differences found.
Perhaps experiments could be done, where different treatment(s) are applied to the scalps of subjects with dandruff and subjects without dandruff, to examine the effect on the scalp microbiome of the subjects. For example, an antifungal shampoo could be applied to both groups, and the abundance/diversity of different microbes could then be determined, to see if the antifungal shampoo affected the two groups differently.
Further Reading:
- For basic information on dandruff, including symptoms, causes, and treatment options: The Mayo Clinic- Dandruff Overview.
- A more technical article about the fungal genus Malassezia, including other health conditions it can be involved in, and factors that are responsible for its overgrowth: Indian Journal of Dermatology- Article on Malassezia.
References:
- Saxena, R. et al. (2018). Comparison of Healthy and Dandruff Scalp Microbiome Reveals the Role of Commensals in Scalp Health. Front. Cell. Infect. Microbiol, Vol. 8, Article 346. DOI: 10.3389/fcimb.2018.00346
- Borda, L. J., Wikramanayake, T. C. (2015). Seborrheic Dermatitis and Dandruff: A Comprehensive Review. J Clin Investig Dermatol, 3(2): 10. DOI: 10.13188/2373-1044.1000019
- Clavaud, C. et al. (2013). Dandruff Is Associated with Disequilibrium in the Proportion of the Major Bacterial and Fungal Populations Colonizing the Scalp. PLoS ONE 8(3): e58203. DOI: 10.1371/journal.pone.0058203
- Soares, R. C. et al. (2016). Dysbiotic Bacterial and Fungal Communities Not Restricted to Clinically Affected Skin Sites in Dandruff. Front. Cell. Infect. Microbiol. 6: 157. DOI: 10.3389/fcimb.2016.00157
- Wang, L. et al. (2015). Characterization of the major bacterial—fungal populations colonizing dandruff scalps in Shanghai, China, shows microbial disequilibrium. Exp Dermatol. 24(5): 398-400. DOI: 10.1111/exd.12684