Relating plaque psoriasis barrier function changes with the underlying skin morphology and physiology

The relationship between skin barrier function and the underlying morphological and physiological changes in disease states remains incompletely characterised. Improved understanding of these relationships is important for informing topical drug development, as disease-driven alterations may directly influence drug delivery at or near the site of action. This study characterised biophysical and structural properties of psoriatic skin in 28 patients with mild-to-severe psoriasis and compared these with measurements from 28 healthy participants. Assessed parameters included transepidermal water loss (TEWL), dermal blood flow, stratum corneum (SC) thickness, viable epidermal thickness, lower SC cell width, skin hydration, temperature, pH, and hair follicle density. Findings were subsequently contextualised against existing literature on skin structure and physiology in psoriasis. TEWL, a key indicator of barrier function, was significantly elevated in psoriatic lesions compared with healthy skin (12.84 vs. 7.14 g/m²/h, P = 0.0011). Lesional skin also demonstrated increased dermal blood flow (123.3 vs. 32.2 perfusion units, P < 0.0001), SC thickness (3.5-fold), viable epidermal thickness (2.2-fold), and lower SC cell width (P < 0.0001). In contrast, skin hydration was significantly reduced (16.7 vs. 102.0 µS, P < 0.001), while elasticity, temperature, pH, and hair follicle density were not significantly different. Non-lesional skin largely resembled healthy skin across measured parameters. These results suggest that blood flow, viable epidermal thickness and SC dimensions are determinants of healthy and psoriatic skin TEWL driving potential differences in drug transport between psoriatic and healthy skin. The robust and comprehensive characterization of the skin barrier in healthy and diseased (lesional and non-lesional psoriatic skin) populations presented here is in agreement with existing literature providing insights on drug absorption and clinical effects in patients with psoriasis.