What causes and treats contact dermatitis with big itchy bumps under bra straps?

Rash Under Bra Straps: Contact Dermatitis Management

Most Likely Diagnosis

Your itchy bumps under bra straps are most likely contact dermatitis—either irritant contact dermatitis (ICD) from friction, sweat, and pressure, or allergic contact dermatitis (ACD) from materials in the bra (elastic, dyes, nickel in hooks, or laundry detergent residue). 1

Immediate Treatment Approach

First-Line Treatment: Topical Corticosteroids + Moisturizers

• Apply hydrocortisone 0.5-1% cream to affected areas 3-4 times daily for mild cases, which temporarily relieves itching associated with minor skin irritations, inflammation, and rashes 2
• For more severe or persistent cases, escalate to mid-potency topical steroids such as triamcinolone 0.1% or high-potency clobetasol 0.05% for 2 weeks 1, 3
• Apply fragrance-free moisturizers immediately after washing the affected area—use at least 2 fingertip units of moisturizer and reapply every 3-4 hours 1
• Use the "soak and smear" technique nightly: soak the affected area in plain water for 20 minutes, then immediately apply moisturizer to damp skin for up to 2 weeks 1

Critical Avoidance Measures

• Immediately stop wearing the offending bra and switch to 100% cotton bras without elastic, underwires, or metal hooks 1
• Wash all bras in fragrance-free, dye-free detergent and avoid fabric softeners, which are common allergens 1
• Avoid washing the area with harsh soaps—use only gentle soap substitutes or emollients 1
• Do not apply products containing topical antibiotics (neomycin, bacitracin) unless specifically indicated, as these can worsen allergic reactions 4, 1

Distinguishing Irritant vs. Allergic Contact Dermatitis

Irritant Contact Dermatitis (80% of cases)

• Caused by friction, pressure, sweat accumulation, and occlusion under tight bra straps 5, 6
• Patients report stinging and burning more than itching 5
• Lesions are typically well-demarcated and confined to areas of direct contact 5
• Occurs immediately or within hours of exposure 6

Allergic Contact Dermatitis (20% of cases)

• Caused by delayed hypersensitivity to bra materials (rubber accelerators in elastic, nickel in hooks, dyes, formaldehyde resins) 1, 6
• Patients report intense itching as the predominant symptom 5
• May spread beyond the area of direct contact 6
• Requires prior sensitization—develops 24-72 hours after re-exposure 6

When Conservative Treatment Fails

Patch Testing Indication

• If dermatitis persists despite 2-4 weeks of topical steroids and allergen avoidance, refer for patch testing to identify specific allergens 1, 3
• Patch testing should include an extended standard series plus specific testing for textile allergens, rubber accelerators, and nickel 1
• Do not apply potent topical steroids to the back within 2 days of patch testing, as this causes false negatives 1

Second-Line Therapies for Refractory Cases

• Consider topical tacrolimus 0.1% where topical steroids are unsuitable or ineffective 1
• Phototherapy (PUVA) is an established second-line treatment for chronic contact dermatitis resistant to topical steroids 1
• Systemic therapies (azathioprine, ciclosporin) may be necessary for severe recalcitrant cases 1

Common Pitfalls to Avoid

• Do not use oil-based moisturizers under occlusive clothing, as they can trap irritants 4
• Avoid excessive occlusion without underlying moisturizer application, which worsens dermatitis 4, 1
• Do not wash the area with very hot water or harsh detergents, which strip the skin barrier 4, 1
• Do not rely on barrier creams alone—they have questionable value and may create false security 1
• Avoid rapid discontinuation of steroids if systemic treatment is needed, as this can cause rebound dermatitis 3

Prognosis and Long-Term Management

• Complete allergen avoidance offers the best chance for resolution 1
• Only 25% of patients with persistent contact dermatitis achieve complete healing, with 50% having intermittent symptoms and 25% having permanent symptoms despite treatment 1
• Early identification and treatment are critical to prevent chronicity 6
• Continue regular moisturizer use even after symptoms resolve to maintain skin barrier function 1