What are the clinical features and treatment of allergic contact dermatitis?

Clinical Features and Treatment of Allergic Contact Dermatitis

Clinical Features

Allergic contact dermatitis (ACD) is a delayed-type hypersensitivity (Type IV) reaction that manifests as eczematous lesions clinically indistinguishable from other forms of dermatitis, requiring patch testing for definitive diagnosis. 1

Acute Phase Presentation

• Erythema and vesiculation are the hallmark features, often with visible borders demarcating the area of contact 1
• Dramatic flares may involve bullae formation in severe cases 2
• Pruritus and burning sensations are common accompanying symptoms 1

Chronic Phase Presentation

• Dryness, lichenification, and fissuring characterize long-standing disease 1
• Scaling and thickened skin develop with repeated exposure 2
• Cracks and fissures may appear, particularly on hands 2

Distribution Patterns Suggesting ACD

• Marked facial and eyelid involvement suggests cosmetic or fragrance allergens 1
• Increased severity at neck flexures indicates jewelry or clothing-related allergens 1
• Vesicular lesions on dorsal hands and fingertips point to occupational exposures 1
• Unusual distributions (e.g., sides of feet) or atypical patterns for atopic dermatitis warrant investigation 1
• Dermatitis on exposed surfaces (face, neck, arms, "V" area of chest) may indicate aeroallergen triggers 1

Common Allergens

• Nickel is the most prevalent contact allergen, followed by fragrances, formaldehyde, preservatives, lanolin, and rubber chemicals 1
• Neomycin-containing preparations cause contact sensitivity in 13-30% of patients with chronic otitis externa 1
• Topical corticosteroids themselves can cause ACD in a small subset of patients, creating diagnostic challenges 1
• Propylene glycol, thimerosal, and benzalkonium chloride in medication vehicles are common culprits 1

Key Diagnostic Pitfall

Pattern and morphology alone are unreliable in distinguishing ACD from irritant or endogenous dermatitis, particularly on hands and face—patch testing is essential when the diagnosis remains uncertain. 1, 3

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Diagnostic Approach

When to Suspect ACD

• Disease aggravated by topical medications or emollients 1
• Patterns reflecting consistent item exposure (e.g., jewelry, gloves) 1
• Later onset of disease or new significant worsening 1
• Persistent dermatitis despite appropriate treatment for other conditions 1
• Refractory symptoms after prolonged use of antimicrobial otic drops (suggesting neomycin sensitivity) 1

Patch Testing Indications

Patch testing should be performed when history or physical exam suggests ACD, when dermatitis has unusual distribution, or when the condition persists despite treatment. 1, 4

• Test to at least an extended standard series of allergens 3
• Sensitivity ranges from 60-80% with specificity of 70-80% 5, 3
• Apply suspected allergens to unaffected skin (typically the back) for 48 hours 1
• Assess reactions at initial patch removal and again up to 7 days later for delayed reactions 1

Critical Testing Precautions

• Do not apply potent topical steroids to the back within 2 days of testing (causes false negatives) 3
• Avoid oral corticosteroids or immunosuppressants during testing; if unavoidable, keep prednisolone ≤10 mg daily 3
• Positive patch tests only indicate sensitization—clinical relevance to active dermatitis must be demonstrated 4

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Treatment Algorithm

Step 1: Allergen Identification and Complete Avoidance

Complete avoidance of the identified allergen is the most critical step and offers the best chance for resolution. 4

• Replace all soaps and detergents with emollients 3
• Substitute materials in contact with affected areas (e.g., fragrance-free detergents, avoid metal belt buckles if nickel-sensitive) 3
• Consider workplace visits if occupational exposure is suspected to identify hidden allergens 3
• For glove-related ACD, use accelerator-free neoprene or nitrile gloves 3, 4

Step 2: First-Line Topical Therapy

For localized acute ACD, apply mid- to high-potency topical corticosteroids such as triamcinolone 0.1% or clobetasol 0.05%. 2

• Topical corticosteroids are the cornerstone of acute treatment 3
• For persistent dermatitis failing lower-potency steroids, escalate to very high-potency agents (clobetasol propionate 0.05%) for 2 weeks 3
• Very high-potency steroids achieve clear or almost clear skin in 67.2% of patients with severe dermatitis versus 22.3% with vehicle 3
• Adverse events are low, with only 0.8% withdrawals in treatment groups versus 11.3% in vehicle groups 3

Step 3: Barrier Restoration

• Apply moisturizers liberally and immediately after washing to repair skin barrier 3
• Use the "soak and smear" technique: soak affected area in plain water for 20 minutes, then immediately apply moisturizer to damp skin nightly for up to 2 weeks 3
• Use moisturizers packaged in tubes rather than jars to prevent contamination 3
• Apply two fingertip units of moisturizer to hands after each washing 3
• Recommended amount: 100g per 2 weeks for trunk area 3

Step 4: Systemic Therapy for Extensive Disease

If ACD involves >20% body surface area, systemic steroid therapy is required and offers relief within 12-24 hours. 2

• For severe rhus (poison ivy) dermatitis, taper oral prednisone over 2-3 weeks 2
• Rapid discontinuation causes rebound dermatitis 2

Step 5: Second-Line Therapies for Refractory Cases

For steroid-resistant chronic ACD, consider topical tacrolimus 0.1%, PUVA phototherapy, azathioprine, or ciclosporin, all supported by prospective clinical trials. 3

• Topical tacrolimus 0.1% is effective and avoids corticosteroid allergy risk, particularly useful for facial dermatitis 3, 4
• PUVA phototherapy is an established second-line treatment for chronic hand dermatitis 3, 4
• For severe chronic hand eczema, alitretinoin is recommended 3
• Azathioprine or ciclosporin may be considered for recalcitrant cases 3

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Protective Measures

Glove Selection and Use

• Use rubber or PVC gloves with cotton liners for household tasks 3
• Remove gloves regularly to prevent sweat accumulation, which aggravates dermatitis 3
• Apply moisturizer before wearing gloves 3, 4
• Latex, vinyl, and nitrile gloves resist breakdown from ethanol or isopropyl alcohol 3
• In occupational settings, select gloves based on specific chemical exposures and consider permeation time—"impervious" gloves have finite protection duration 3

Barrier Cream Limitations

Barrier creams alone have questionable value and should not be over-promoted, as they may create false security and reduce implementation of appropriate preventive measures. 3

• After-work creams have demonstrated benefit in reducing irritant contact dermatitis incidence 3

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Critical Pitfalls to Avoid

• Facial steroid use: Exercise extreme caution with topical corticosteroids on facial skin—prolonged use causes skin thinning, telangiectasia, perioral dermatitis, and red face syndrome due to increased percutaneous absorption 3
• Avoid washing with dish detergent or other known irritants 3
• Do not use very hot or very cold water for washing 3
• Avoid disinfectant wipes for hand cleaning 3
• Do not apply products containing topical antibiotics without indication 3
• Avoid prolonged occlusion without underlying moisturizer application 3
• Do not continue exposure to suspected allergens—this prevents healing and leads to persistent dermatitis 4

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Prognosis

• Allergic contact dermatitis usually carries a worse prognosis than irritant dermatitis unless the allergen is identified and avoided. 1, 5
• Complete resolution is expected if the causative agent is identified and completely avoided 4
• For occupational ACD, prognosis is often poor: only 25% achieve complete healing, 50% have periodic symptoms, and 25% have permanent symptoms 3
• Changing occupation does not improve prognosis in 40% of cases 3
• Chronicity is most common in those allergic to nickel and chromate 1
• Early identification and complete avoidance of allergens offers the best chance for resolution 3

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Special Considerations

ACD in Atopic Dermatitis Patients

• ACD is increasingly recognized in individuals with atopic dermatitis, with prevalence of 6-60% depending on the study 1
• ACD is at least as common in atopic dermatitis patients as in the general population 1
• Because ACD manifests as eczematous lesions, it is clinically indistinguishable from atopic dermatitis 1

Corticosteroid Allergy

• A small subset of patients develop ACD to topical corticosteroids themselves, posing diagnostic dilemmas 1
• Patch testing to corticosteroid allergens is necessary when this is suspected 3

Neomycin Sensitivity in Otitis Externa

• Allergic contact dermatitis of the external auditory canal can result in refractory acute otitis externa with prolonged antimicrobial otic drop use 1
• Sensitization occurs over 10-14 days, with subsequent delayed-type hypersensitivity causing erythema, pruritus, inflammation, edema, and persistent otorrhea 1
• Blisters and vesicles may be present in severe cases, with reactions extending beyond the ear canal to surrounding skin and neck 1