About This Page
This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
Key points
- Irritant (~80%): non-immune, dose-dependent (water, detergents). Allergic (~20%): type IV delayed hypersensitivity
- Common allergens: nickel, fragrances, preservatives, rubber chemicals, paraphenylenediamine (hair dye)
- Distribution matches exposure — hands (occupational), wrists (nickel jewellery), face (cosmetics)
- Patch testing is the gold standard for allergic contact dermatitis
- Management: allergen/irritant avoidance, emollients, topical corticosteroids
Overview
Contact dermatitis is inflammation caused by direct skin contact with an external substance. Irritant contact dermatitis (~80%) is non-immune and dose-dependent. Allergic contact dermatitis (~20%) is a type IV delayed hypersensitivity reaction requiring prior sensitisation. Common allergens include nickel, fragrances, preservatives (methylisothiazolinone), rubber accelerators, and paraphenylenediamine.
Epidemiology
One of the most common occupational skin diseases. ICD common in healthcare workers, hairdressers, cleaners. Nickel allergy affects ~10-15% of women. Significant occupational morbidity and sickness absence.
Clinical Features
Symptoms
Eczematous rash in distribution matching contactant exposure
Intense pruritus
Acute: vesicles, weeping. Chronic: dry, lichenified, fissured
Occupational pattern — worse during working week, improves on holiday
Signs
Hands: dorsum (irritant) or fingers (allergen) — commonest occupational site
Face/eyelids: cosmetics, hair dye
Wrists/earlobes: nickel (jewellery, watch straps)
Well-demarcated eczematous patch matching contactant distribution
Investigations
First-line
Clinical history + distributionDetailed occupational and exposure history is essential
Second-line
Patch testingGOLD STANDARD for allergic contact dermatitis. Applied to back 48 hours, read at 48 and 96 hours
Management
BAD Guidelines + NICE CKS1
Identification and avoidance
- Identify causative substance via history and patch testing
- Avoidance is the cornerstone
- Workplace modifications if occupational
2
Emollients and barrier protection
- Regular emollients as soap substitute
- Barrier creams, cotton-lined gloves for wet work
3
Topical corticosteroids
- Moderate-potent TCS for flares on hands/body
- Mild TCS for face and flexures
Complications
- Secondary infection: S. aureus superinfection
- Chronic hand eczema: May be disabling
- Occupational impact: Job loss, retraining
UKMLA Exam Tips
- 1Distribution matching exposure = KEY diagnostic clue
- 2Patch testing diagnoses ALLERGIC contact dermatitis (type IV). Does NOT diagnose irritant
- 3Nickel is the most common contact allergen
- 4Paraphenylenediamine (PPD): hair dye and henna tattoos — common exam allergen
- 5Latex allergy causing urticaria is type I (IgE) — NOT the same as contact dermatitis (type IV)
Put your reading into practice
Topic-specific question practice is not linked for this article yet.
Choose UKMLA questions from the existing bank. General exam practice covers your selected topics; it is not filtered to this article. Your usual question-bank access applies.
Choose UKMLA practiceAfter your session, return to this section to revisit the reading and choose your next review.
Verified Sources & References
related resources
Save your place and choose what comes next
Dermatology · Article 9 of 25