What is the diagnosis and treatment for a 32-year-old male with a pruritic (itchy), erythematous (red) rash on the flexor surfaces of the upper and lower extremities, around the left nipple, and on the torso and back, after recently cleaning a house?

Differential Diagnosis: Contact Dermatitis (Irritant or Allergic)

The most likely diagnosis is contact dermatitis—either irritant or allergic—triggered by cleaning products used during house cleaning, and this should be treated with mid-to-high potency topical corticosteroids and strict avoidance of the causative agent. 1

Clinical Reasoning

The presentation strongly suggests contact dermatitis based on several key features:

• Temporal relationship: The rash developed after cleaning a house, providing clear exposure to potential irritants or allergens (soaps, detergents, cleaning chemicals) 2, 1
• Distribution pattern: Flexor surfaces of extremities and scattered truncal involvement are consistent with contact dermatitis, where the substance contacted the skin during cleaning activities 1, 3
• Morphology: Erythematous, pruritic rash without vesicles or pustules fits the clinical picture of contact dermatitis 1, 3
• Progression: The rash becoming painful with movement (especially behind knees) suggests inflammation intensifying in flexural areas where friction occurs 1

Key Differentiating Features to Assess

Irritant vs. Allergic Contact Dermatitis:

• Irritant contact dermatitis occurs immediately after exposure in all individuals in a dose-dependent manner, caused by direct chemical damage from acids, alkalis, or strong cleaning agents 2
• Allergic contact dermatitis occurs only in sensitized individuals and requires prior exposure, with symptoms appearing 24-72 hours after re-exposure 2, 1

Other Differential Diagnoses to Exclude:

• Atopic dermatitis: Would typically have a chronic history starting in childhood, involvement of multiple body areas with characteristic distribution (antecubital/popliteal fossae), and features like xerosis, lichenification, or hyperpigmentation 2
• Miliaria rubra: Would show discrete pustules in intertriginous areas with recent heat/humidity exposure, not primarily flexor surfaces 4
• Scabies: Look for burrows, inguinal/genital involvement, and nocturnal pruritus worsening 4
• Eczematous dermatitis: Would show oozing, crusting, and less discrete borders 2, 4

Treatment Algorithm

First-Line Treatment (Localized Disease)

For rash involving <20% body surface area:

• Apply triamcinolone 0.1% cream twice daily to affected areas for 7-14 days 5, 1
• Alternative: clobetasol 0.05% for more severe inflammation 1
• Hydrocortisone 1% can be used for milder areas or facial/intertriginous involvement (3-4 times daily) 6

Second-Line Treatment (Extensive Disease)

For rash involving >20% body surface area:

• Initiate oral prednisone tapered over 2-3 weeks (typically starting at 40-60 mg daily) 1
• Rapid discontinuation causes rebound dermatitis—the taper must be gradual 1
• Relief typically occurs within 12-24 hours of starting systemic steroids 1

Essential Supportive Measures

• Immediate avoidance of all cleaning products and potential irritants 1, 3
• Use emollients (non-greasy moisturizers) after bathing to maintain skin barrier 4
• Switch to dispersible cream as soap substitute—avoid all soaps and detergents 4
• Apply cool compresses to reduce inflammation and pruritus 4
• Keep affected areas dry and avoid occlusive clothing 4

Symptomatic Management

• Oral antihistamines (cetirizine 10 mg, loratadine 10 mg, or fexofenadine 180 mg daily) for pruritus control 2
• Antiseptic washes (chlorhexidine or benzoyl peroxide) if secondary bacterial infection is suspected 4

Critical Pitfalls to Avoid

• Do not use potent topical corticosteroids in intertriginous areas (behind knees, axillae) due to increased absorption and risk of skin atrophy—use hydrocortisone 1% instead 4, 6
• Avoid greasy ointments as they can inhibit wound exudate absorption and promote superinfection 4
• Do not discontinue steroids abruptly if systemic therapy is required—this causes severe rebound dermatitis 1
• Mark the borders of lesions with ink and observe for 24-48 hours if there is diagnostic uncertainty between contact dermatitis and other conditions 2

When to Escalate Care

If the diagnosis remains uncertain or treatment fails after 2 weeks:

• Perform patch testing to identify specific allergens 1
• Consider skin biopsy if urticarial vasculitis is suspected (painful lesions lasting >48 hours, systemic symptoms) 7
• Reassess for alternative diagnoses including atopic dermatitis, psoriasis, or systemic causes of pruritus 2

Confirmation Strategy

To confirm contact dermatitis as the diagnosis:

• Determine if the rash resolves with strict avoidance of cleaning products over 1-2 weeks 1
• If symptoms recur with re-exposure to cleaning agents, this confirms the diagnosis 1, 3
• Document which specific products were used during cleaning for future avoidance 1