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Dermatology

Contact Dermatitis

Contact dermatitis is eczema caused by an external contactant: irritant disease is dose-dependent barrier injury, whereas allergic disease is a delayed T-cell-mediated reaction in a sensitised person.

In a nutshell

Contact dermatitis is eczema caused by an external contactant. Irritant disease is direct dose-dependent barrier damage, commonly from wet work, soaps or detergents; allergic disease is a delayed type IV reaction after sensitisation. Diagnose from the pattern and exposure history, use specialist patch testing for suspected allergy, and manage with avoidance, barrier care, appropriate topical corticosteroids and selective treatment of infection.

Classic presentation

A healthcare worker develops painful fissured hand eczema after frequent handwashing and glove use, or a patient develops itchy sharply demarcated eczema beneath a watch strap several days after wearing it.

Key points

  • Irritant contact dermatitis needs no prior sensitisation and is related to the intensity, frequency and duration of exposure.
  • Allergic contact dermatitis is delayed type IV hypersensitivity; patch testing, not IgE testing, investigates it.
  • Distribution and timing often identify the contactant: hands, eyelids, hairline, feet, jewellery or workplace exposure.
  • Avoidance and barrier protection are the main long-term treatment; use a site- and severity-appropriate topical corticosteroid for active inflammation.
  • Do not equate weeping or crusting with bacterial infection: follow NICE NG190 and do not routinely give antibiotics to people who are not systemically unwell.
  • Persistent, recurrent, severe, occupational or unexplained dermatitis needs dermatology or occupational-health input.
  • Painful rapidly progressive disease, systemic illness, extensive blistering, mucosal involvement or punched-out vesicles requires urgent reassessment.

First-line investigation

Clinical examination with a detailed product, occupational and exposure history; refer for patch testing when allergic contact dermatitis is suspected or the cause remains unclear.

Management

Exclude severe infection or widespread disease

  • Assess systemic state, pain, spread, blistering, mucosal or eye involvement and vesicles; escalate urgently for suspected cellulitis, sepsis, necrotising infection or eczema herpeticum.4,1,3

Map the rash to the exposure

  • Ask what touches the affected site at work, home and during hobbies, including water, detergents, cosmetics, metals, hair products, gloves and medicines; document timing and improvement away from exposure.1,2

Remove exposure and repair the barrier

  • Avoid or substitute the contactant, reduce wet work, use suitable gloves and apply frequent emollients or soap substitutes; provide practical workplace prevention advice.3,5,1

Treat the flare and infection selectively

  • Use a site- and severity-appropriate topical corticosteroid according to BNF or local formulary advice. Continue anti-inflammatory and emollient treatment during suspected infection, reserving antibiotics for clinically indicated cases under NICE NG190.4,3,6

Patch test and refer persistent disease

  • Refer for specialist patch testing when allergy is suspected, the cause is unclear or disease persists; involve occupational health where work exposure, health surveillance or employment is affected.3,5

Safety-net and prevent recurrence

  • Review exposure control, treatment use and response, and give clear advice to seek help for rapid worsening, systemic illness, spreading infection, severe pain, eye or mucosal involvement or failure to improve.4,1

Exam traps

  • Allergic contact dermatitis is type IV delayed hypersensitivity, not an IgE-mediated allergy.
  • Irritant contact dermatitis can affect anyone after sufficient exposure and commonly affects wet-work hands.
  • A positive patch test is not automatically causal; it must match the exposure and clinical pattern.
  • Crusting or weeping alone does not prove bacterial infection, and antibiotics are not routine when the patient is systemically well.
  • Gloves can protect against exposure but sweating, occlusion and glove materials can also worsen dermatitis.
  • Do not miss eczema herpeticum, cellulitis or necrotising infection in a rapidly worsening or systemically unwell patient.

Illustrations

Well-demarcated eczema conforming to a metal contact site, typical of allergic contact dermatitisA clinical photograph of sharply demarcated eczema at a jewellery or jean-stud contact site, illustrating a contact pattern rather than a generalised eczema distribution.Maria Sieglinda von Nudeldorf, Wikimedia Commons · CC-BY-SA-4.0
Patch testingA clinical photograph of standardised patch-test allergens applied to marked sites on the upper back before delayed readings are assessed.Jan Polák, Wikimedia Commons · CC-BY-SA-3.0

Key sources

  1. NHS: Contact dermatitis (Current NHS overview of symptoms, irritant and allergic causes, trigger avoidance, emollients, topical corticosteroids and referral for persistent or severe disease; accessed 4 August 2026.)
  2. HSE: Work-related skin disease—contact dermatitis (UK Health and Safety Executive professional guidance on irritant and allergic mechanisms, occupational clues and exposure assessment; accessed 4 August 2026.)
  3. British Association of Dermatologists: Contact dermatitis patient information leaflet (BAD consensus information on irritant and allergic contact dermatitis, patch testing, avoidance, emollients, topical treatment and specialist referral; updated June 2025 and accessed 4 August 2026.)Updated 1 Jun 2025
  4. NICE NG190: Secondary bacterial infection of eczema and other common skin conditions (NICE antimicrobial-prescribing pathway for suspected secondary bacterial infection of eczema, including when not to swab or prescribe antibiotics, reassessment and referral; published 2 March 2021 and accessed 4 August 2026.)Updated 2 Mar 2021
  5. HSE: Dermatitis in health and social care (Current HSE guidance on wet work, risk assessment, skin protection and health surveillance in health and social care; accessed 4 August 2026.)
  6. British National Formulary (BNF) (BNF online prescribing information for topical corticosteroids, emollients and antimicrobial treatment; current prescribing details must be checked at the point of care; accessed 4 August 2026.)

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.