What are the causes of dandruff?

Dandruff appears as a result of an acceleration of skin cell renewal associated with abnormal desquamation, meaning dead cells are produced in excessive amounts. The epidermal cells, not fully mature, stick together and shed in clusters: dandruff flakes. This process results from various causes.

Like the skin, the scalp is a living ecosystem inhabited by billions of coexisting microorganisms: bacteria, fungi, and, to a lesser extent, viruses and mites. This community forms the scalp microbiota, whose balance is essential for maintaining healthy skin. Disruption of this balance can lead to the development of dandruff in the hair.

A 2015 study by ZHANG and colleagues sheds new light on this subject by sequencing the DNA of microorganisms present on the scalp of 363 volunteers, with or without dandruff. The researchers showed that two bacterial genera dominate this ecosystem: Cutibacterium (formerly known as Propionibacterium) and Staphylococcus. Under normal conditions, these two populations coexist and regulate one another. However, in individuals with dandruff, this balance is disrupted: Cutibacterium, sharply decreases, while Staphylococcus proliferates. Furthermore, the researchers demonstrated that the severity of dandruff was directly correlated with this shift: the greater the proportion of Staphylococcus increases, the more visible the flakes become.

With respect to fungi, the genus Malassezia is also involved in the onset of dandruff. This lipophilic yeast is naturally present in the majority of individuals. Among its species, Malassezia restricta and Malassezia globosa dominate the scalp. However not all strains have the same impact. Certain variants of M. restricta are strongly associated with the presence of dandruff, while others appear rather neutral or even protective. This finding underscores the importance of intra-species differences, and explains why some individuals can harbor large populations of Malassezia without developing dandruff in their hair.

Another noteworthy aspect is that the bacterial and fungal communities seem to operate independently rather than synergistically. More precisely, it isn't necessarily the direct interactions between bacteria and fungi that trigger dandruff, but rather the specific balance shifts within each group. However, the dynamic between Cutibacterium and Staphylococcus could play a role. Indeed, Cutibacterium produces free fatty acids and bacteriocins capable of limiting the growth of Staphylococcus. When this protective population declines, the scalp becomes more favorable to the proliferation of Staphylococcus, and thus to dandruff.

It is therefore not the presence or absence of a specific type of microorganism that explains dandruff, but rather an imbalance in the scalp microbiota.

Sebum is often blamed when it comes to dandruff. This lipid film, secreted by the sebaceous glands, actually serves an essential protective function : it lubricates the scalp, maintains hydration, and forms a natural barrier against external aggressors. But, as is often the case in biology, balance is key: too little sebum weakens the skin, while too much alters the cutaneous ecosystem.

The previously cited ZHANG study also analyzed the relationship between sebum and dandruff. The researchers found that sebum production varies with age: it peaks between 20 and 39 years old, then tends to decline after 40. At first glance, one might expect younger individuals to be more affected by dandruff. However, the opposite is true: older adults often exhibit more flakes despite having less abundant sebum. This paradox shows that sebum alone is not the direct culprit, but that it acts in interaction with the microbiome and the skin barrier.

The effect that sebum depends primarily on its composition. Rich in triglycerides and wax esters, it serves as a genuine nutrient source for lipophilic microorganisms, notably yeasts of the genus Malassezia. These yeasts produce lipase enzymes capable of hydrolyzing sebum triglycerides and releasing free fatty acids. Among them, certain unsaturated fatty acids are known irritants: they disrupt the cohesion of corneocytes in the stratum corneum and increase the permeability of the skin barrier. Consequently, the skin becomes weakened, local inflammation sets in, and scaling intensifies.

Sebum also influences the bacterial population on the scalp. For example, Cutibacterium utilizes certain lipids as energy substrates. Its presence, beneficial under balanced conditions, is linked to the production of organic acids and antimicrobial compounds that limit the growth of competing bacteria such as Staphylococcus. An imbalance in sebum composition can therefore disadvantage some bacterial populations in favor of others, indirectly contributing to the development of dandruff.

Finally, beyond its composition, sebum also acts by modulating transepidermal water loss. Indeed, a deficiency or poor quality of sebum can exacerbate water leakage through the epidermis, further compromising the skin barrier. The study shows that areas of the scalp with elevated transepidermal water loss are also those where dandruff is most pronounced.

Sebum should not be viewed as an isolated factor but rather as a modulator of scalp homeostasis.

Although imbalances in the cutaneous microbiota and changes in sebum quantity and quality are major factors, individuals do not all respond similarly to these disturbances. The development of dandruff also depends on personal characteristics—whether physiological, genetic, or related to localized variations on the scalp.

ZHANG’s study demonstrates that age influences the onset of dandruff. Adults between 40 and 59 years old generally exhibit more dandruff than younger individuals, despite lower sebum production. This phenomenon is explained by several factors associated with skin aging : the skin barrier becomes less efficient, natural hydration declines, and the composition of the microbiome evolves over time. Together, these changes make the scalp more vulnerable to inflammation and flaking.

The genetics also affect the skin’s response. Certain individual variations in sebum lipid composition, cytokine production, or barrier integrity can make some people more prone to irritation or imbalances in the microbiome. Moreover, Zhang’s study highlights that the mere presence of Malassezia is not sufficient to trigger dandruff: it’s the specific strains and their interactions with the scalp that matter. Some individuals tolerate high populations of Malassezia without any symptoms, while others develop pronounced flaking at similar levels.

Individual susceptibility, shaped by genetic background as well as by each person’s physiological and immunological history, is a factor to consider in the development of dandruff.

Note : Stress is often cited as an aggravating factor in dandruff, but the direct evidence of a link remains limited. Some studies, particularly among adolescents, have not shown a direct association between stress levels and the onset of dandruff. Nevertheless, stress can influence scalp health by modulating sebaceous gland activity, a factor involved in dandruff development. Further research is therefore necessary to draw definitive conclusions about the influence of stress on dandruff occurrence.

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• WIKRAMANAYAKE C. & al. Seborrheic dermatitis and dandruff: A comprehensive review. Journal of Clinical and Investigative Dermatology (2015).

• ZHANG M. & al. Dandruff is associated with the conjoined interactions between host and microorganisms. Scientific Reports (2015).

• SHARMA V. K. Comparison of healthy and dandruff scalp microbiome reveals the role of commensals in scalp health. Frontiers in Cellular and Infection Microbiology (2018)

• JEGOU-PENOUIL M.-H. Les pellicules. Dermato-info (2019).

• LIANA D. F. & al. The relationship of stress level to the incidence of pityriasis capitis (dandruff) in students at SMK Panca Karsa Sungai Pinyuh. Enrichment: Journal of Multidisciplinary Research and Development (2023).