FFinalistSouthampton · 2027
Dermatology
AKT · Dermatology/Inflammatory & papulosquamous

Contact dermatitis

Irritant (direct toxicity) or allergic (type IV delayed hypersensitivity)

Overview

An eczematous reaction to an external agent. Two mechanisms: IRRITANT contact dermatitis (non-immune direct toxicity — the commonest, e.g. soaps, water, detergents) and ALLERGIC contact dermatitis (a type IV delayed hypersensitivity to a sensitiser, e.g. nickel, fragrances, chromate, hair-dye PPD). The distribution mirroring an exposure is the clue.

Recognise

  • Eczematous change (acute: erythema, vesicles, oozing; chronic: dryness, fissuring, lichenification) at the site of contact
  • Distribution mirrors the exposure — nickel under jewellery/earlobes, occupational on the hands, allergens on the face from cosmetics
  • Irritant: stinging/burning, sharply confined to contact area; allergic: itch predominates, may spread beyond contact site

Red flags

  • Severe occupational/hand disease threatening work; airborne or widespread facial involvement

Differentials & how to tell them apart

Atopic dermatitis/eczemaflexural with a personal/family atopy history, not confined to a contact site
Irritant vs allergic contact dermatitispatch testing separates them — only allergic gives a positive delayed patch reaction
Tineaannular, active scaly edge, KOH positive
Psoriasiswell-demarcated silvery plaques, extensor

Clinical image

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Contact dermatitis — clinical imagesDermNet

Investigations

Irritant contact dermatitis is a clinical diagnosis. Patch testing identifies the responsible allergen in suspected ALLERGIC contact dermatitis (and confirms relevance).

Management

Identify and avoid the trigger + emollients and a topical corticosteroid for the flare

  1. 1Avoid the irritant/allergen + emollients/soap substitute + a topical corticosteroid (potency matched to severity and site).Gate: Persistent dermatitis, or a distribution suggesting a specific sensitiser, warrants PATCH TESTING — it confirms allergic contact dermatitis; irritant contact dermatitis is non-immune and will not patch-test positive
  2. 2Occupational disease → protective measures, gloves, occupational-health referral. Severe/extensive → dermatology; a short oral corticosteroid course occasionally needed.
Emollients + soap substitute — barrier repair; avoid the trigger
Topical corticosteroids — potency matched to severity/site for the flare
Potassium permanganate soaks — for acute weeping/vesicular lesions

Key points

Nickel is the commonest contact allergen. Hand dermatitis is frequently irritant and occupational. Avoidance is curative; continued exposure makes it chronic.

Monitor & prognosis

Resolution after avoidance; recurrence indicates ongoing exposure.

Resolves with avoidance; becomes chronic if the exposure continues.

Source: NICE CKS Dermatitis - contact