Background/Aims: Establishing dermal penetration rates is important to better understand the safety of topically applied materials, especially for premature infant skin with compromised skin barrier function. Skin prematurity involves thinner stratum corneum and underdeveloped epidermis/dermis resulting in decreased barrier function, higher transepidermal water loss and greater chemical penetration, when compared to healthy full-term neonate/adult skin. Methods: We developed an in vitro skin penetration model using human ex vivo skin to estimate penetration for premature/compromised skin barrier conditions by tape stripping. Skin barrier deficiency was characterized by transepidermal water loss. Baby wipe lotion containing 5 mg/cm² [¹⁴C]-PEG-7 phosphate was applied 5 times to human skin samples of intact, moderately or highly compromised skin barrier and once at 25 mg/cm² over 24 h. Results: Overall penetration of [¹⁴C]-PEG-7 phosphate was low (<5%) even for highly compromised skin. The absorption rate was higher (p < 0.001) for compromised skin versus intact skin. No significant difference was seen between moderately and highly compromised skin by repeated dosing. Under single-dose conditions, penetration through highly compromised skin was significantly higher compared to intact skin (p = 0.001). Conclusion: Our model demonstrates that even under highly compromised skin conditions, penetration of [¹⁴C]-PEG-7 phosphate is low (<5%) and only 4-6 times higher compared to mature/intact skin and does not approach 100%. Penetration was unaffected by single or multiple dosing conditions.

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Dandruff and seborrhoeic dermatitis are accompanied by bothersome itch. We have established a novel non-invasive methodology to sample histamine levels in the stratum corneum in order to facilitate an understanding of pruritogenesis in this condition. Histamine levels were assessed in two groups of subjects with dandruff before and after 3 weeks of treatment with a commercial potentiated zinc pyrithione shampoo. A comparative population without dandruff was also studied. Itch self-perception was quantified on a visual analogue scale. The histamine level in subjects with dandruff was more than twice that in those who did not have dandruff. Under conditions known to resolve flaking symptoms, the shampoo led to a reduction in histamine in subjects with dandruff to a level that was statistically indistinguishable from those who did not have dandruff. This reduction in histamine was accompanied by a highly significant reduction in the perception of itch intensity. These findings suggest an association between the subjective perception of itch in the scalp and the level of histamine in the skin.

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