What causes white scaly patches on the skin?

White Scaly Patches on Skin: Causes and Differential Diagnosis

The most common causes of white scaly patches on skin are pityriasis versicolor (a fungal infection caused by Malassezia species) and pityriasis alba (a benign hypopigmented condition, particularly in children). 1, 2

Primary Fungal Cause: Pityriasis Versicolor

Pityriasis versicolor is a superficial fungal infection presenting as hypopigmented or hyperpigmented macules with fine scale, most commonly affecting the upper trunk, neck, and upper arms. 1, 2, 3

Key Clinical Features:

• Scaly, discolored patches that can be hypopigmented (most common at 85.8% of cases) or hyperpigmented 4
• Distribution: Predominantly chest (31.8%), back (19.4%), shoulders, and upper arms 3, 4
• Scale character: Fine, characteristic scaling that becomes more apparent with gentle scraping 3
• Mild pruritus may be present in approximately 23.8% of patients 4

Causative Organism and Pathogenesis:

• Malassezia species (lipophilic yeast) converts from blastospore to pathogenic mycelial form under predisposing conditions 5, 6
• Predisposing factors include: high temperatures, high humidity, excessive sweating (31.8% of cases), oily skin (21.1%), occlusive clothing (19.4%), outdoor occupation, and immunosuppression 5, 4
• Recurrence is common (60% of patients report recurrent episodes) 4

Diagnostic Confirmation:

• Wood's lamp examination shows yellowish-white or copper-orange fluorescence, helping distinguish from other conditions 2
• KOH preparation reveals the pathognomonic "spaghetti and meatballs" appearance (short hyphae and round yeast cells) 2, 3
• Clinical diagnosis is often sufficient given characteristic appearance 3

Secondary Common Cause: Pityriasis Alba

Pityriasis alba presents as pale, hypopigmented patches with fine scale, particularly common in children, and represents a benign condition often confused with vitiligo. 1

Distinguishing Features:

• Age group: Predominantly affects children 1
• Appearance: Pale patches with fine scale, less distinct borders than vitiligo 1
• No complete depigmentation (unlike vitiligo which shows complete melanocyte loss) 1, 7

Critical Differential Diagnoses to Exclude

Vitiligo:

• Complete depigmentation (white patches) without scale, resulting from melanocyte loss 7
• Distribution patterns: Non-segmental (symmetrical) or segmental (unilateral/dermatomal) 7
• Wood's lamp enhances visualization of depigmented areas 7
• Key distinction: Vitiligo lacks the fine scale characteristic of pityriasis conditions 1, 7

Other Scaly Conditions:

• Psoriasis: Thick, silvery-white scales on erythematous plaques, often with characteristic distribution (extensor surfaces, scalp) 8
• Seborrheic dermatitis: Greasy yellowish scaling in sebaceous areas (scalp, face, central chest), associated with Malassezia 8, 5
• Eczema/atopic dermatitis: Chronic pruritus with erythema, xerotic scaling, and lichenification 8
• Tinea corporis: Annular scaly patches with active advancing border, caused by dermatophyte fungi (not Malassezia) 3

Treatment Approach for Pityriasis Versicolor

Topical antifungal therapy is the primary treatment, with systemic therapy reserved for extensive or recurrent cases. 2, 5, 3

First-Line Topical Options:

• Ketoconazole shampoo or other imidazole preparations 5, 3
• Selenium sulfide 2.5% 5, 3
• Zinc pyrithione shampoo 5, 3
• Ciclopirox olamine 3

Systemic Therapy (for extensive/recurrent cases):

• Fluconazole or itraconazole for short-term treatment in difficult cases 5

Prevention of Recurrence:

• Prophylactic treatment regimen is mandatory to prevent recurrence, particularly during warm, humid periods 5, 3
• Lifestyle modifications: Avoid excessive heat/humidity, wear loose-fitting breathable clothing, maintain good hygiene 2, 3

Common Pitfalls to Avoid

• Failing to recognize hypopigmented pityriasis versicolor as a fungal infection rather than vitiligo or pityriasis alba 1, 9
• Not performing KOH preparation when diagnosis is uncertain, missing the characteristic fungal elements 2, 3
• Inadequate treatment duration or failure to implement prophylactic measures, leading to high recurrence rates 5, 3
• Expecting rapid repigmentation: Hypopigmentation may persist for months after successful fungal eradication and is difficult to improve even with UV therapy 9
• In immunocompromised patients, fungal infections may be more widespread and resistant to treatment, requiring more aggressive management 2