Dislodgeable stratum corneum exfoliation: role in percutaneous penetration?

Abstract

Background: Stratum corneum (SC) readily dislodgeable exfoliation could affect percutaneous absorption and thus influence treatment and toxicological effects. Urea, a classical enhancer, is absorbed less than 1% in vivo in man and might be a useful marker to quantify chemical-drug exfoliation. This study develops a simple model utilizing washing and tape-stripping to quantify surface loss of chemicals topically applied on human skin and estimate the extent of chemical-drug SC exfoliation.

Methods: Urea, 10% as a model hydrophilic chemical marker, was applied to human skin on identical sites (5 cm²/area with 1.8 mg/cm² urea) in vitro and in vivo. At time points 0, 4, and 6 h, the area was washed, rubbed, and stripped five times with cellophane tape. Quantitative urea was performed by colorimetric assay.

Results: The data of the in vitro protected non-exfoliating model, as the control, showed no statistical difference between 0-, 4-, and 6-h recovery (P > 0.05). In the air-exposed model in vivo exfoliation in man, the recovery decreased from 98.8 ± 3.7% to 93.9 ± 6.8% in 4 h and 86.4 ± 3.0% in 6 h (P = 0.02). In the cloth-covered model in vivo, the recovery decreased from 99.4 ± 5.8% to 84.9 ± 5.3% in 4 h (P = 0.04), which reached 73 ± 2.8% within 6 h (P = 0.007).

Conclusions: This study suggests that urea, measured with washing, rubbing, and tape-stripping, can be used as a possible chemical-drug SC readily dislodgeable exfoliation and friction rubbing metric. In addition, this might help to determine the rule of skin exfoliation in dermatopharmacologic and dermatoxicologic assessment.

Keywords::

• Metrics
• percutaneous penetration
• readily dislodgeable stratum corneum exfoliation
• tape stripping; urea

Acknowledgements

The authors greatly appreciate the assistance of Wei Lai, M.D., Fabrice Pirot, Ph.D., Hongbo Zhai, M.D., Xiaoying Hui, M.D., Maxime Fougere, Ph.D, and Tita Reyes. Anonymous reviewers greatly improved the usefulness of the data by suggesting the use of description—“readily dislodgeable” SC.

Declaration of interest

The authors declare that there are no conflicts of interest.