Which skin condition increases penetration of topical medications?

• A. Acne
• B. Eczema
• C. Rosacea
• D. Psoriasis

Answer: (B)

The main idea is that how much a topical drug penetrates depends on the integrity of the skin’s outer barrier, especially the stratum corneum. In eczema (atopic dermatitis), this barrier is defective due to genetic factors and inflammation, leading to disrupted lipids, reduced filaggrin function, and increased transepidermal water loss. Those changes create more intercellular space and hydration, so drugs can diffuse more readily into deeper skin layers and even enter the systemic circulation. Because of this barrier compromise, topical medications tend to penetrate more easily in eczema than in healthy skin.

The other conditions don’t consistently produce the same level of barrier disruption. Acne centers on hair follicles and sebum, not primarily on barrier permeability. Rosacea involves vascular and inflammatory features rather than a widespread barrier defect. Psoriasis often thickens the stratum corneum, which can hinder penetration unless the skin is severely inflamed or fissured, so its effect on permeability is not as straightforward as eczema.