What is the likely diagnosis for a Continuous Positive Airway Pressure (CPAP) wearer with inflamed red skin, itching, and bumps in areas where the CPAP mask straps are, and could it be an allergic reaction to the mask material if the lesions are localized only to these areas?

CPAP-Related Contact Dermatitis

The most likely diagnosis is irritant contact dermatitis from mechanical friction and pressure of the CPAP mask straps, and if the red patches are localized only to strap contact areas with no other body involvement, this strongly suggests a contact-related etiology rather than a systemic dermatologic condition. 1

Primary Diagnosis: Irritant Contact Dermatitis

The clinical presentation—inflamed red skin with itching and bumps precisely where CPAP straps contact the skin (periauricular area and strap distribution)—is pathognomonic for irritant contact dermatitis (ICD), which occurs through direct mechanical friction and pressure causing physical damage to the epidermis without immune system involvement. 1, 2

• The periauricular area is particularly vulnerable because constant pressure and friction from CPAP head straps creates a dose-dependent inflammatory response based on duration and pressure of contact. 1
• ICD manifests as erythema, edema, scaling, pruritus, and can progress to vesicles or blisters in severe cases—all confined to the distribution of strap contact. 1, 3
• The fact that lesions are only present where straps contact skin and nowhere else on the body is the critical diagnostic feature distinguishing this from systemic dermatologic conditions like atopic dermatitis or generalized allergic reactions. 1, 4

Alternative Diagnosis: Allergic Contact Dermatitis

If the dermatitis persists despite equipment modification or extends beyond the primary contact area, consider allergic contact dermatitis (ACD) to CPAP materials. 1, 4

• ACD is a type IV delayed hypersensitivity reaction to specific materials in CPAP equipment, most commonly silicone in mask cushions and seals, or rubber accelerators (particularly dialkyl thioureas) in neoprene straps. 5, 1, 6
• Unlike ICD, ACD requires prior sensitization and can spread to adjacent skin areas beyond the direct contact zone. 1, 4
• ACD typically carries a worse prognosis than ICD unless the specific allergen is identified and completely avoided. 4, 7
• Clinical features alone cannot reliably distinguish ICD from ACD—both present with erythema, scaling, and pruritus in contact distribution. 4, 3

Immediate Management Algorithm

Step 1: Equipment Modification (First-Line, Curative)

• Immediately replace neoprene or rubber straps with cloth alternatives, as material substitution is often curative. 1, 6
• Assess mask fit to reduce excessive pressure—improper fitting causes both increased friction (worsening ICD) and air leaks. 5, 1
• Consider switching to adjustable masks or custom-made masks that better conform to facial anatomy. 5

Step 2: Skin Barrier Restoration

• Apply fragrance-free, preservative-free oil-based emollients frequently to moisturize and prevent cracking. 1, 7
• Keep the affected area dry during treatment and use protective barriers when showering to prevent secondary infection. 1

Step 3: Anti-Inflammatory Therapy

• Apply mid- to high-potency topical corticosteroids (triamcinolone 0.1% or clobetasol 0.05%) to affected areas 3-4 times daily for at least 7 days, even if symptoms improve sooner. 1, 8, 3
• For children under 2 years or mild cases, hydrocortisone 1% may be used. 7, 8
• If corticosteroids are insufficient, consider calcineurin inhibitors as alternative anti-inflammatory agents. 1

Step 4: Diagnostic Confirmation if Treatment Fails

• If dermatitis persists after equipment modification and topical therapy, perform patch testing to identify specific allergens. 4, 6, 3
• Patch testing has 60-80% sensitivity and requires assessment at 48 hours and again up to 7 days for delayed reactions. 4, 7
• Test both the North American Contact Dermatitis Group standard allergens and samples of the patient's actual CPAP equipment materials. 6

Critical Pitfalls to Avoid

• Never continue using the same CPAP equipment if dermatitis develops—ongoing exposure perpetuates inflammation and risks progression to chronic dermatitis with lichenification and fissuring. 1, 4
• Avoid neomycin-containing topical preparations in the periauricular area, as 5-15% of patients with chronic external otitis develop contact sensitivity to neomycin. 1
• Do not add antimicrobial therapy routinely—antibiotics should only be used if secondary infection develops (purulence, warmth, spreading erythema beyond contact zone). 1
• Avoid scratching or traumatizing affected skin, as this worsens inflammation and creates portals for bacterial entry. 1
• Do not discontinue topical corticosteroids prematurely—continue for at least 7 days even if symptoms improve, as early discontinuation risks rebound dermatitis. 1, 3

Prognosis

Complete resolution is expected if the causative agent (mechanical friction or specific allergen) is identified and eliminated. 7 ICD generally has better prognosis than ACD if the irritant is removed, whereas ACD requires complete avoidance of the specific allergen for resolution. 4, 7 Chronic cases develop when triggers are not identified or eliminated, leading to persistent barrier dysfunction. 7