An open assay model to induce subclinical non‐erythematous irritation

Abstract

To avoid the acute irritation and dryness that a single occlusive surfactant application (24-h patch test) may cause, and to approximate clinical use, an open application model was chosen to define subclinical non-erythematous irritation in the stratum corneum. This human test combined a supervised washing at the laboratory with at-home use of the test products by the subjects. Effects of washing with the surfactants on the dorsal hand and volar forearm were compared. The results demonstrated that this situational use model permits the exploration of subclinical surfactant-induced irritation. The forearm appeared to be more discriminative as compared to the dorsal hand. Squamometry proved to be a sensitive, complementary assessment method for detecting surfactant-induced subclinical skin surface alterations and for differentiating surfactant effects in this open assay.

Dirt-binding particles consisting of hydrogenated castor oil beads constitute a nonirritating alternative for abrasive cleaning of recalcitrant oily skin contamination in a three-step programme of occupational skin protection

“…5,11 Protected sites (like the forearm), as chosen in our washing model, have been shown to be more discriminating in an open assay approximating clinical use, as the hands, especially the dorsum, are more exposed to external stresses which probably enhance the effects of the surfactants. 19 In our repetitive washing model (modified from Gehring et al 11 ) we demonstrated that abrasive cleansing constitutes a relevant irritation factor in vivo for the intact human skin. For direct comparison of the properties of walnut shell powder and the castor wax beads on human skin in vivo concerning their irritant potency and cleaning power, no commercial ready-to-use formulas were compared due to their confounding additional ingredients.…”

Assessment of the Subclinical Irritation of Surfactants: A Screening Open Assay Model

“…However, other testing surfactants (except SLS) did not show a significant difference. Squamometry has proved a sensitive assessment for detecting surfactant-induced subclinical irritation [1][2][3]. It has shown its superiority in the evaluation of efficacy of moisturizers and barrier creams against surfactant irritant [10,11].…”

“…Finally, the investigator scored the disks in a blinded manner with a microscope at 30 magnifications according to the following scales [1][2][3]. Intercorneocyte cohesion used: 0 = large sheet; 1 = large clusters + few isolated cells; 2 = small clusters + many isolated cells; 3 = clusters in disruption, most cells isolated; 4 = all cells isolated, many cases of lysis.…”

“…Visual scoring was judged according to the following rating scale [1][2][3]: for erythema, 0 = no redness, 1 = very slight redness, 2 = slight redness, 3 = moderate redness, 4 = strong redness, 5 = very strong redness, 6 = extreme redness; for dryness, 0 = no dryness, well hydrated and completely smooth, 1 = very slight, dry without scaling, no whitening in the ridges, 2 = slight dryness, dry with possibly very slight powdering, 3 = moderate dryness, scaling is obvious, mainly on limited areas, scales are small, 4 = strong dryness, same as score of 3, but on a larger surface, 5 = very strong, scales are larger in size in some areas, small cracking can be seen, slightly rough surface, 6 = extreme dryness, large scales on large surface + cracking + roughness.…”

“…Previously, an open application method utilizing an exaggerated forearm washing model has demonstrated its superiority in determining subclinical (nonerythematous) surfactant irritant effects [1][2][3]. To screen numerous surfactants, we modified this model in combination with a novel stratum corneum metric.…”