Skip to main content
ChenDermatologist
ChenDermatologist
Dr. Chen Yi-Jia · Dermatology Notes
English version. Prefer Traditional Chinese? Switch to Chinese
Patient guide · Environment / Occupation Per BAD 2017 + ICDRG · Updated 2026-05-08

Contact dermatitis — complete patient guide
ACD vs ICD, patch testing, allergen avoidance

Contact dermatitis is redness, itching, and scaling caused by skin contact with an external substance. It has two major types: allergic contact dermatitis (ACD), in which T cells recognize a specific allergen (classic examples: nickel, fragrance, preservatives, PPD hair dye); and irritant contact dermatitis (ICD), in which the substance directly damages the skin barrier without immune memory. Identifying type + culprit + avoidance is the cornerstone of treatment.

Note:This article is for general education only. If you suspect contact dermatitis — especially recurrent or occupation-related rashes — please see a dermatologist; patch testing must be interpreted by a trained dermatologist.
Key Fact (Johnston 2017, BJD)

Contact dermatitis accounts for 70–90% of occupational skin disease — hairdressing, healthcare, food service, cleaning, and mechanical industries are the most affected.Nickel is the most common allergen worldwide. Once sensitized to an allergen, the reaction is lifelong and the allergen must be avoided permanently.

What is contact dermatitis?

Contact dermatitis is a skin reaction with redness, itch, scaling, and vesicles after contact with an external substance. It splits into two categories:

  • Allergic contact dermatitis (ACD) — type IV delayed hypersensitivity (T-cell mediated). Requires prior sensitization; small amounts trigger reaction; latency 24–72 hours after exposure. Common allergens: nickel, fragrance mix, MI/MCI, PPD, rubber chemicals.
  • Irritant contact dermatitis (ICD) — direct physical/chemical damage to the stratum corneum. Dose- and time-dependent; affects anyone. Common: soaps, detergents, frequent hand-washing, organic solvents. Accounts for ~80% of all contact dermatitis.

Diagnosis: patch testing

Patch testing is the gold standard for ACD diagnosis (Johnston 2017, BJD ). The European baseline series with ~30 standardized allergens is applied to the back for 48 hours, then read at 48 and 96 hours per ICDRG criteria (and at 7 days for selected agents like PPD, neomycin, corticosteroids). A positive result indicates sensitization but must be correlated to actual exposure (relevance assessment, BAD ).

Treatment ladder

  • Step 1 — Avoidance + barrier protection: tailored allergen avoidance after patch test; daily emollient, occupational gloves (nitrile/vinyl, not latex if rubber-allergic).
  • Step 2 — Topical therapy: topical corticosteroid for active flares (potent for hands/trunk, mild for face/folds); calcineurin inhibitors (tacrolimus/pimecrolimus) for thin-skin sites.
  • Step 3 — Refractory chronic disease: NB-UVB phototherapy (Goulden 2022, BJD), oral alitretinoin (UK indication for chronic hand eczema), short oral prednisolone bursts, ciclosporin or methotrexate per BAD prescribing guidelines, dupilumab and JAK inhibitors as emerging options.

Occupational contact dermatitis

Contact dermatitis accounts for 70–90% of occupational skin disease. Highest-risk occupations: hairdressing, healthcare, food handling, metalworking, cleaning, construction. BAD 2017 emphasizes a workplace visit and employer-led exposure modification. About 50% of occupational contact dermatitis persists even after exposure stops, but earlier diagnosis and intervention improve prognosis.

Bottom line

Contact dermatitis is treatable and preventable, but only if the trigger is identified. Distinguish ACD vs ICD, refer for patch testing when indicated, and combine precise avoidance, barrier care, and topical therapy for flares. For recurrent hand, face, neck, or genital eczema — especially work-related — see a dermatologist for patch testing instead of cycling through "sensitive skin" products.