What causes red sores on the head, dandruff, and small hair follicles with hairless long strands in an adult or adolescent?

Red Sores, Dandruff, and Hair Loss: Differential Diagnosis

The combination of red sores on the scalp, dandruff-like scaling, and hair loss with broken hair strands most strongly suggests tinea capitis (scalp ringworm), which requires fungal culture confirmation and oral antifungal treatment. 1

Primary Diagnostic Considerations

Tinea Capitis (Most Likely)

• Inflammatory tinea capitis presents with diffuse pustular lesions, patchy alopecia coexisting with scattered pustules or low-grade folliculitis, and painful regional lymphadenopathy 1
• The "diffuse scale" variant can present as generalized scaling resembling dandruff with minimal or absent alopecia 1
• Endothrix infection with Trichophyton species produces non-inflammatory patches of alopecia with fine scale, studded with broken-off, swollen hair stubs creating a "black dot" appearance 1
• Diagnosis requires fungal culture for confirmation and to guide systemic therapy, as clinical diagnosis alone is insufficient 1
• Treatment requires oral antifungal therapy; topical treatment alone is inadequate 2

Seborrheic Dermatitis (Alternative Diagnosis)

• Presents with scaling, erythema, and itching most often on the scalp, face, chest, back, axilla, and groin 3
• Results from inflammatory response to Malassezia yeast colonization 3, 4
• Clinical presentation ranges from mild patches to diffuse scalp scaling, with yellowish, scaly patches in severe cases 4
• Diagnosis is clinical based on location and appearance of lesions 3
• Treatment involves topical antifungals (ketoconazole, ciclopirox) as mainstay therapy, with short-term topical corticosteroids for inflammation 3, 4

Scalp Folliculitis

• Multiple infectious agents (bacteria, viruses, fungi) and noninfectious causes can present as folliculitis 5
• Diagnosis occasionally requires histologic confirmation and cannot be based solely on clinical appearance 5

Critical Diagnostic Algorithm

Step 1: Examine Hair Loss Pattern

• Look for "black dot" appearance (broken-off hair stubs) which indicates endothrix Trichophyton infection 1
• Check for exclamation mark hairs (short broken hairs at expanding margins) which are pathognomonic for alopecia areata 2
• Assess whether hair loss is patchy or diffuse 2

Step 2: Assess Inflammatory Features

• Red sores with pustules and painful lymphadenopathy strongly suggest inflammatory tinea capitis or kerion 1
• Simple scaling without significant inflammation favors seborrheic dermatitis 3, 4

Step 3: Mandatory Laboratory Testing

• Fungal culture is mandatory before initiating treatment when tinea capitis is suspected 1, 2
• Specimens should be collected by plucking hairs, using blunt scalpel to remove hair and scalp scale, or taking scalp brushings 1
• The most common cause of treatment failure is incorrect diagnosis made on clinical grounds alone 2

Common Pitfalls to Avoid

• Do not misdiagnose inflammatory tinea capitis (kerion) as bacterial abscess, though secondary bacterial infection should not be overlooked 1
• Do not rely solely on clinical appearance for diagnosis of folliculitis; histologic confirmation may be necessary 5
• Do not initiate treatment without fungal culture when tinea capitis is suspected, as this leads to treatment failure 2
• Do not confuse seborrheic dermatitis with psoriasis vulgaris, atopic dermatitis, or candidiasis in the differential diagnosis 6, 7

When to Consider Alternative Diagnoses

• If hair loss is patchy with well-demarcated areas and exclamation mark hairs without significant scaling, consider alopecia areata (autoimmune T-lymphocyte mediated) 2, 8
• If patient has personal or family history of autoimmune disease with nail changes (pitting, ridging), alopecia areata becomes more likely 2, 8
• Dermoscopy showing yellow dots, exclamation mark hairs, and cadaverized hairs confirms alopecia areata 2
• If scaling is prominent on face, chest, and flexural areas in addition to scalp, seborrheic dermatitis is more likely 3, 4, 6