What could be the cause of a recurring round dermatitis dry patch on my arm that didn't respond to antifungals or antibiotics, but improved with hydrocortisone (Cortizone) ointment?

Recurring Round Dermatitis Patch: Most Likely Diagnosis and Management

Your recurring round dermatitis patch that responded temporarily to hydrocortisone but returned after stopping treatment is most consistent with either nummular (discoid) eczema or allergic contact dermatitis, and you should see a dermatologist for patch testing to identify potential allergens and consider stronger topical corticosteroids or alternative treatments for long-term control. 1

Why This Pattern Suggests Specific Diagnoses

Key Clinical Features Point to Eczematous Dermatitis

• The round (nummular) shape, dryness, and lack of response to antifungals definitively rules out fungal infection, which was appropriate to exclude first 2
• The temporary improvement with hydrocortisone followed by recurrence is classic for inflammatory dermatitis conditions that require ongoing management rather than short-term treatment 3, 2
• The fact that it didn't respond to antibiotics suggests this is not primarily an infectious process 2

Two Most Likely Diagnoses

Allergic Contact Dermatitis (ACD):

• ACD manifests as eczematous lesions that are often clinically indistinguishable from other forms of dermatitis and can present as localized round patches 1
• The recurrence pattern suggests ongoing exposure to an allergen that you're contacting repeatedly in that specific location 1
• Common allergens include nickel (jewelry, watch bands, belt buckles), fragrances, preservatives in lotions/creams, rubber chemicals, and even ingredients in topical medications you may be applying 1
• A small subset of patients can even develop allergic contact dermatitis to topical corticosteroids themselves, which could explain why it improved initially but returned 1

Nummular (Discoid) Eczema:

• This presents as coin-shaped (round) patches of dermatitis that are characteristically dry and scaly 2
• It typically requires longer-term management rather than short courses of treatment 3
• Often recurs in the same location 2

What You Should Do Next

Immediate Management Steps

Continue Basic Skin Care:

• Apply fragrance-free moisturizers with petrolatum or mineral oil immediately after bathing to damp skin, as these are most effective and least allergenic 4
• Use lukewarm or cool water for washing rather than hot water, which damages the skin barrier 3, 4
• Pat dry gently rather than rubbing the affected area 3, 4
• Avoid harsh soaps, detergents, and fragrances on or near the affected area 4

Topical Corticosteroid Adjustment:

• The 1% hydrocortisone you used is a low-potency steroid that may be insufficient for this condition 2
• For localized dermatitis patches, mid- to high-potency topical steroids like triamcinolone 0.1% or clobetasol 0.05% are more effective 2
• However, be cautious with prolonged use as this can cause skin atrophy and other complications 5

Critical Next Step: See a Dermatologist

You need patch testing to identify potential allergens:

• Patch testing should be considered for persistent or recalcitrant dermatitis not responding to standard therapies, which describes your situation 1
• The American Academy of Dermatology recommends referral to dermatology for suspected allergic contact dermatitis requiring patch testing 3
• Patch testing involves placing suspected allergens on unaffected skin (typically the back) for 48 hours, with readings at removal and again at days 4-7 1
• The sensitivity of patch testing ranges from 60-80%, and positive results must be correlated with your clinical history 1

Timing for dermatology referral:

• You should be referred when dermatitis does not improve after 6 weeks of treatment or when there is recurrent disease 3
• Your two-month recurrence clearly meets this criterion 3

Think About Potential Triggers

Before your dermatology appointment, consider:

• Does anything touch that specific area repeatedly? (watch band, bracelet, clothing with metal snaps, elastic, specific fabric) 1
• Do you apply any lotions, creams, or products to that area? 1
• Is there any occupational exposure or hobby-related contact? 1
• Have you started using any new personal care products, detergents, or soaps? 1

Important Pitfalls to Avoid

Common mistakes that worsen dermatitis:

• Don't apply known irritants like dish detergent or harsh soaps to the area 3
• Avoid using very hot water for washing 3, 4
• Don't use superglue to seal any cracks or fissures that may develop 3
• Avoid prolonged, continuous use of topical corticosteroids without medical supervision, as this can cause skin atrophy, telangiectasia, and even worsen the condition 5
• Don't assume the hydrocortisone "cured" the problem just because it temporarily improved - inflammatory dermatitis often requires ongoing management 3, 2

If Patch Testing is Positive

Once allergens are identified:

• Strict avoidance of the identified allergen with resolution of the corresponding dermatitis confirms the diagnosis 1
• Your dermatologist will provide specific alternative products you can safely use 6
• Avoidance is the definitive treatment for allergic contact dermatitis 1

If No Allergen is Found or Condition Persists

For recalcitrant cases:

• Consider stronger topical steroids, phototherapy, or systemic therapy options 3
• The British Association of Dermatologists recommends considering topical tacrolimus when topical steroids are unsuitable or ineffective 1
• For severe chronic cases, alitretinoin or PUVA therapy may be considered 1, 3