Pityriasis (Tinea) Versicolor

Definition

Pityriasis (Tinea) versicolor is a superficial fungal infection of the skin caused by Malassezia species, characterized by hypo- or hyperpigmented scaly macules, primarily on the trunk and proximal extremities.

Epidemiology

• Common worldwide, especially in tropical and subtropical climates with high humidity.
• Most frequent in adolescents and young adults due to increased sebaceous gland activity.
• Recurrence is common, especially in warm climates.
• No gender predilection, though more noticeable in darker skin tones.
• Malassezia is part of normal skin flora; infection occurs when it shifts from yeast to pathogenic hyphal form under favorable conditions.

Etiology

• Causative organisms: Malassezia furfur, Malassezia globosa, and other lipophilic yeasts.
• Predisposing factors include hot and humid climate, excessive sweating, oily skin, tight clothing, malnutrition, and immunosuppression.
• Proliferation of the yeast leads to disruption of normal skin pigmentation by interfering with melanin synthesis.
• Not considered contagious as the organism is part of the normal cutaneous flora.

Pathophysiology

• Malassezia species convert from the commensal yeast form to a pathogenic mycelial form under humid or oily conditions.
• Produces azelaic acid and other dicarboxylic acids that inhibit tyrosinase activity in melanocytes, leading to hypopigmentation.
• Local inflammation and keratinocyte turnover can cause hyperpigmentation in some cases.
• Limited to the stratum corneum; does not invade deeper dermal layers.
• Recurrences occur due to persistence of yeast in hair follicles and sebaceous glands.