Contact Dermatitis

Common allergens include: nickel, fragrances, preservatives, rubber (gloves), hair dye, adhesives, and topical antibiotics. Even tiny quantities of allergen can trigger a rash.

📖 About

• Itchy inflammatory skin condition caused by an allergic immune reaction to a contact substance.
• Chronic or recurrent if exposure continues.

🧬 Aetiology & Pathophysiology

• Type IV (delayed) hypersensitivity reaction.
• 1️⃣ Initial sensitisation → allergen processed by Langerhans cells → memory T-cells generated in lymph nodes.
• 2️⃣ Re-exposure → T-cell activation → cytokine release → inflammatory skin reaction.
• Onset: typically 48–72 hours after allergen contact.

⚡ Common Allergens

• 💍 Nickel (jewellery, watch straps, belt buckles).
• 🧴 Fragrances & preservatives (methylisothiazolinone in wipes, hair products).
• 🧤 Rubber/latex (gloves – accelerators, thiurams, carbamates).
• 🎨 Hair dye (para-phenylenediamine, PPD).
• 💅 Acrylates (artificial nails, nail cosmetics).
• 💊 Topical medications (especially antibiotics such as neomycin).

👩‍🏭 Occupations at Risk

• 🔧 Metal workers.
• 💇 Hairdressers, beauticians, nail technicians.
• 🧑‍⚕️ Healthcare workers (glove use, antiseptics).
• 🧹 Cleaners, painters, florists.

🩺 Clinical Features

• Localized eczema-like rash at site of allergen contact:
  • Nickel → wrist eczema from watch strap.
  • Plaster adhesive → dermatitis under strapping.
  • Rubber gloves → hand dermatitis.
  • Methylisothiazolinone in wipes → facial eczema.
• Symptoms: redness, itching, vesicles, scaling, lichenification if chronic.
• Can spread beyond initial contact site in severe cases.

🔍 Differentials

• Irritant contact dermatitis – from soaps, detergents, solvents, water exposure; more common in atopic patients.
• Contact urticaria – immediate wheals (minutes–hours), e.g. latex.
• Fungal infections – ring-shaped lesions, positive microscopy/culture.

🧪 Investigations

• Patch testing is the gold standard to identify allergens.
• Skin biopsy in severe/atypical cases (shows spongiotic dermatitis).

💊 Management

• 🎯 Avoidance of identified allergen (confirmed via patch test + history).
• 🧤 Protective measures: appropriate gloves, barrier creams.
• 🧴 Topical therapy: emollients, topical corticosteroids for flares.
• 🦠 Secondary infection: topical or oral antibiotics as required.
• 💊 Severe/recalcitrant disease:
  • Short courses of oral corticosteroids.
  • Immunosuppressants: azathioprine, ciclosporin, methotrexate.
  • Topical calcineurin inhibitors (tacrolimus, pimecrolimus).

🧾 Clinical Case Examples – Contact Dermatitis

Case 1 – Irritant 🧴 A 28-year-old nurse develops red, cracked, itchy hands after frequent hand washing. 👉 Diagnosis: Irritant contact dermatitis. 👉 Management: emollients, barrier creams, reduce exposure.

Case 2 – Allergic 💍 A 35-year-old woman has an itchy blistering rash on her wrist 2 days after wearing a new bracelet. 👉 Diagnosis: Nickel allergy (allergic contact dermatitis). 👉 Management: remove allergen, topical steroids.

Case 3 – Occupational 👷 A 50-year-old builder presents with a scaly rash on hands/forearms worsened by cement exposure. 👉 Diagnosis: Allergic contact dermatitis (chromates in cement). 👉 Management: protective gloves, avoid allergen, topical steroids.

📚 References

• British Association of Dermatologists – Contact Dermatitis Guidelines.
• Rook’s Textbook of Dermatology.
• DermNet NZ – Allergic Contact Dermatitis