Dermatology · UKMLA & AKT
Allergic contact dermatitis
A free high-yield preview for the UKMLA Applied Knowledge Test. Below are the key points to recognise allergic contact dermatitis — the full SA Note notes add investigations, management, complications and 10 practice questions.
Key high-yield points
- ACD = Type IV (delayed-type) hypersensitivity - T-cell mediated, no antibodies involved
- Sensitisation phase (clinically silent): allergen → Langerhans cell antigen presentation → memory T-cells generated
- Elicitation phase: re-exposure → memory T-cell activation → cytokine release → eczematous rash after 24-72 hours
- Patient may use a product for months/years before sensitisation - absence of previous reaction does NOT exclude ACD
- Common allergens: nickel (most common - jewellery, watches, belt buckles), rubber/latex (condoms, gloves), paraphenylenediamine/PPD (hair dye, black henna), fragrances, acrylates, preservatives (methylisothiazolinone), topical medications (neomycin, lanolin)
Latex condoms are an important cause of pruritus vulvae - contact dermatitis is the most common cause of pruritus vulvae overall.
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