Dandruff and hair loss have a relationship most people don't know about. A 2025 review just mapped the mechanism.

Malassezia is a lipophilic yeast naturally present on all human scalps — it is part of the normal scalp microbiome. The problem is not its presence but its dominance. When Malassezia overgrows — due to excess sebum production, compromised skin barrier, disrupted acid mantle pH, or immune dysregulation — it hydrolyzes sebaceous triglycerides and releases unsaturated fatty acids that affect the scalp environment, causing oxidative damage and inflammatory skin reactions.

This is the sebum oxidation mechanism covered in the PIILIF article — and SD is the clinical condition that makes it pathological rather than subclinical. The same antifungal botanical compounds that the Laritelle formula contains (patchouli's patchoulol, clove bud's eugenol) are directly relevant: both demonstrate documented antifungal activity against Malassezia species — the primary driver of seborrheic dermatitis.

The immune response to Malassezia-released fatty acids involves Th1 and Th17 lymphocyte activation — exactly the T-cell pathway that the alopecia areata article identified as the primary autoimmune mechanism in AA. In SD, this is not an autoimmune attack on the follicle per se — it is an immune response to the Malassezia-generated lipid inflammatory substrates that, when chronic, creates a scalp-wide cytokine environment that the follicle grows in continuously.

The cytokines produced by Th1/Th17 activation — TNF-α, IL-17, IL-22, interferon-gamma — are the same inflammatory mediators that the PIILIF research described finding around the upper hair follicle in 81% of AGA patients. SD is generating, continuously, the cytokine environment that PIILIF describes as damaging the follicle stem cell niche.

Seborrheic dermatitis both causes and is perpetuated by skin barrier dysfunction — the barrier disruption that allows Malassezia to proliferate is worsened by the Malassezia-driven inflammation, creating a self-reinforcing cycle. This is the scalp pH and barrier story that has appeared across the clean beauty, hard water, shampoo protocol, and hair dye articles — all of those factors (alkaline shampoos, hard water mineral deposition, chemical processing) are contributing to the barrier disruption that perpetuates the SD cycle.

Conversely, pH-balanced shampoo formulated at 5.5 — which supports the acid mantle and protective Cutibacterium populations — is directly interrupting this cycle at the barrier level. The caffeine article confirmed that topical caffeine also reduces Malassezia and increases Cutibacterium. The formula is working on the SD mechanism through multiple simultaneous pathways.

Malassezia is lipophilic — it feeds on the fatty acids in sebum. Excess sebum production is the primary environmental factor that enables Malassezia overgrowth, and sebum excess is itself driven by DHT (which stimulates sebaceous gland activity through androgen receptor signalling). This creates a direct mechanistic link between androgenic hair loss and seborrheic dermatitis: DHT stimulates sebum → excess sebum feeds Malassezia → Malassezia drives the Th1/Th17 inflammatory cascade → that cascade feeds the PIILIF inflammatory environment around the follicle. In women with androgenetic alopecia, these two pathways are not running separately. They are amplifying each other.