16th July 2026

Allergic contact dermatitis

Clinical features

Allergic contact dermatitis is associated with Type IV hypersensitivity reaction. It requires previous exposure to the substance (sensitisation). Rash usually takes around 48-72 hours after the exposure to appear. Usually confined to contacted area, but can sometimes extend outside the contacted area or may be generalised. Reaction usually produces erythema, oedema and blisters.  Diagnosis usually can be made with detailed and careful history taking on exposure to common allergens.

Common sources of allergic contact dermatitis include

• Nickel, Chromate
• Hair dyes(paraphenylenediamine), tights, shoes
• Creams, ointments, cosmetics

Investigations

• Diagnosis is mainly from history taking and clinical examination. 
• Patch testing may be used to distinguish between allergic and contact dermatitis. 

Management

• Avoid all potential irritants 
• Emollient 
• Barrier creams +/- topical steroids.