Atopic Eczema — SCE Dermatology MCQ

Correct answer: C — Wet wraps enhance percutaneous absorption of topical corticosteroid by up to 10-fold through occlusion and hydration of the stratum corneum

Option C is correct: wet wraps enhance percutaneous absorption of topical corticosteroid by up to 10-fold through occlusion and hydration of the stratum corneum. The damp inner layer hydrates the stratum corneum, swelling corneocytes and disrupting the intercellular lipid lamellae, while the outer dry layer occludes the skin, preventing evaporation and trapping the corticosteroid against the surface for longer. This markedly increases drug flux across the epidermis, which is why only diluted (often 50 percent) corticosteroid preparations are used under wet wraps, and why treatment is time limited to avoid excessive local and systemic steroid exposure. This mechanism, and the resulting need for caution, is recognised in UK eczema management guidance, which restricts occlusive wet wrap use with topical corticosteroids to short courses under specialist direction. Why the other options are wrong: D. Act as sunscreen: wet wraps have no photoprotective properties; they are bandaging layers over emollient or corticosteroid, not UV filters, and provide no barrier against ultraviolet radiation. A. Purely for emollient delivery: while emollients are frequently used under wraps and benefit from the same occlusive hydration, the question specifically describes corticosteroid-containing wraps, and the enhanced percutaneous absorption effect applies directly to the active corticosteroid, not just emollients. B. Reduce the corticosteroid strength: the wrap itself does not dilute the drug; dilution is achieved separately by mixing the corticosteroid with emollient before application, whereas the wrap increases, not reduces, effective potency through enhanced absorption. E. Provide antibiotic delivery: wet wraps contain no antimicrobial component; they are not indicated as a delivery system for antibiotics, and infected eczema is a caution against their use. Key point: Occlusion plus hydration under wet wraps can increase topical corticosteroid absorption up to tenfold, so diluted preparations and short treatment courses are required to avoid local and systemic steroid toxicity.

Reference: Cochrane Database of Systematic Reviews, Different strategies for using topical corticosteroids in people with eczema (2022 update), PMC8916090, https://pmc.ncbi.nlm.nih.gov/articles/PMC8916090/