Pityriasis Sicca: Characteristics of the Flakes
The flakes seen in pityriasis sicca (dandruff) are fine, white to gray, superficial scales that represent abnormal desquamation of the stratum corneum, often associated with Malassezia yeast overgrowth. 1
Clinical Characteristics of the Flakes
Appearance and Distribution
- Fine, white to gray scales that are loosely adherent to the scalp surface, easily shed onto clothing and shoulders 1
- The scales represent superficial flaking but lead to significant structural changes in the stratum corneum beneath 2
- Distribution is typically diffuse across the scalp, particularly in seborrheic areas 3
Pathophysiology of Scale Formation
- The flaking results from accelerated epidermal turnover and abnormal keratinization of the stratum corneum 2
- Malassezia (Pityrosporum) yeast plays a pathogenetic role in the formation of these scales, with numerous yeasts often visible microscopically in the squamae 1
- The process involves inflammatory biomarkers and alterations in sebaceous secretion, not just simple surface scaling 2
Differential Considerations
Distinguishing from Other Scalp Conditions
When evaluating scalp flakes, consider these key differentiating features:
- Tinea capitis with diffuse scale: May present similarly to dandruff but typically shows some degree of alopecia or broken hairs, unlike pityriasis sicca which preserves hair 4
- Psoriasis: Produces thick, silvery scales with well-demarcated erythematous plaques, contrasting with the fine, loose scales of pityriasis sicca 4
- Seborrheic dermatitis: Often overlaps with pityriasis sicca but may show more greasy, yellowish scales (pityriasis steatoides) rather than the dry, fine scales of pityriasis sicca 5
Clinical Pitfall
The term "pityriasis sicca" specifically refers to the dry variant with fine white scales, as opposed to pityriasis steatoides which has oilier, more adherent scales 1. This distinction is important for treatment selection, though both respond to antifungal therapy targeting Malassezia.