Marc Paye

EEMCO Guidance for the in vivo Assessment of Skin Greasiness

Sebaceous gland activity has four distinct components which are sebum production (a secretion rate function), storage (a volume function), surface output (a delivery rate function) and stratum corneum permeation (an influx rate function). The oily appearance of skin results from an excess of sebum excretion and spreading over the body surface and its interaction with the skin surface. A multi-pronged approach is often useful to assess skin greasiness with precision. The clinical evaluation of skin greasiness and its shiny appearance should be further complemented by quantifying the large pores, follicular plugs and comedones. The sebum amount present at the skin surface can be measured non-invasively using one of several methods based on solvent extraction, cigarette paper pads, photometric assessment, bentonite clay and lipid-sensitive tapes. Quantitative parameters include the sebum casual level, the sebum excretion rate, the sebum replacement time, the instant sebum delivery, the follicular excretion rate, the density in sebum-enriched reservoirs and the sustainable rate of sebum excretion. A series of environmental and biological features influence the data. Hence rigorous methodological designs are mandatory to support claims. As a rule, accuracy of the methods is adversely affected by skin temperature, degree of hydration and surface roughness. An additional confounding factor is the inherent difficulty of collecting the surface lipids without a contribution from the follicular reservoir. A better understanding of factors that alter the sebum amount at the skin surface may well assist in the development of sebosuppressive agents to help the reduction of the skin greasiness and improve acne.

Use of the Reviscometer® for measuring cosmetics‐induced skin surface effects

Background/purpose: The Reviscometer® RVM600 that measures resonance running time (RRT) has been shown to be inversely related to the skin stiffness. However, very few publications describe the use of this instrument for testing the effect of cosmetic products.

Comparison of in vitro predictive tests for irritation induced by anionic surfactants

Skin compatibility of anionic surfactants may often but not always he predicted by vitro tests. For instance, the correlation between in vivo and in vitro data is classically hampered in the presence of magnesium. This ion is known to interfere with in vitro skin irritation predictive test based on protein denaturation. This study was conducted to compare a recently introduced assay, corneosurfametry, with other in vitro tests including the pH‐rise of bovine serum albumin, collagen swelling, and zein solubilization tests. Corneosurfametry entails collection of eynoacrylate skin surface strippings and short contact time with surfactants, followed by staining samples with toluidine blue and basic fuchsin dyes. Measurements are made by reflectance colorimetry. Data show that irritation potentials predicted by corneosurfametry agree with those obtained by established in vivo and in vitro irritation tests. Moreover, corneosurfametry data are not artificially lowered by addition of magnesium in surfactant solutions. In conclusion, corneosurfametry should be viewed as one of the realistic predictive tests for surfactant irritancy.

Subclinical, non-erythematous irritation with an open assay model (washing): sodium lauryl sulfate (SLS) versus sodium laureth sulfate (SLES)

Compared to exaggerated hand washing procedures, an open non-exaggerated assay better approximates consumer surfactant use. Our goal was to observe skin surface modifications induced by an open test with regard to discriminating between surfactant solutions. This human in vivo assay provided information about the effect of only three washes at the laboratory and a week of at-home use. Dorsal hand and volar forearm were compared. The results demonstrated that this clinical model permits exploration of subclinical surfactant-induced irritation. Both the volar forearm and the dorsal hand are capable of discriminating between the effects of sodium lauryl sulfate (SLS) and sodium laureth sulfate (SLES). Squamometry proved to be a sensitive assessment technique for detecting surfactant-induced subclinical skin surface alterations and for differentiating surfactant effects in this open application assay, in as few as three washes.

Dansyl chloride labelling of stratum corneum: its rapid extraction from skin can predict skin irritation due to surfactants and cleansing products

The irritation potential of surfactants and body cleansing products was determined by evaluating the removal of dansyl chloride from the skin. Dilute solutions (2% active ingredient, w/v) of surfactants and soap extract fluorescence from the skin within 30 min. This is probably a physicochemical effect as it is too rapid to be due to a modification of epidermal cell turnover rate. Such an extraction of the fluorescent dye occurs without any clinical sign of irritation. However, it may represent an early phase of skin irritation process, because it is related to the ranking of irritant products as determined by other assessment methods.

A comparative study of the effects on the skin of a classical bar soap and a syndet cleansing bar in normal use conditions and in the soap chamber test

Background/aims: The skin irritation potential of a body cleansing product is often compared under exaggerated test conditions, although the product is intended to be used at home with repetitive and brief contact with the skin. The aim of this study was to determine how much patch testing is predictive of the clinical, sub‐clinical and subjective cutaneous effects of products used at home by consumers for their normal hygienic cleansing.

A Hand Immersion Test under Laboratory-Controlled Usage Conditions: The Need for Sensitive and Controlled Assessment Methods

Exaggerated test conditions were frequently used to investigate the cutaneous tolerance of detergent products in the past. As the sensitivity of newly designed biometric methods is steadily improving, the trend towards more realistic test conditions should be encouraged. A hand immersion test under laboratory‐controlled usage conditions is presently described, fulfilling such principles. Panelists soaked their hands in 2 different hand dishwashing liquids, 2× daily for 10 min each (with successive in‐solution/out‐of‐solution cycles) for 4 consecutive days. Products were at usual dilution for dishwashing liquids and were randomized between the dominant and non‐dominant hands of panelists. Visual scoring of erythema and dryness developing on the whole hands (scoring scales including interdigital areas and joints) during the week did not allow discrimination between the 2 products. However the dominant hands were significantly more susceptible to alterations than the non‐dominant hands, regardless of product attribution. In contrast, skin electrical measurements (Corneometer® CM800 and Skicon® 200) on the dorsum of the hands (muscle mass between thumb and index) and squamometry analysis of tape stripping (harvested from the same site) yielded significant differences between the 2 products. In conclusion, a hand immersion test under realistic conditions has been described, which discriminates between products when sensitive assessment methods are used to explore skin sites partially protected from daily‐life skin aggressions.

Open application assay in investigation of subclinical irritant dermatitis induced by sodium lauryl sulfate (SLS) in man: advantage of squamometry

Background/aims: After a single occlusive application (24 h patch test), SLS can cause irritation, dryness, and tightness. In typical use, clinical surfactant exposure is usually brief, of open application, and cumulative. The open application model becomes relevant when phenomena, such as dryness and subclinical, i.e., non‐visible, irritation are induced.

An open assay model to induce subclinical non‐erythematous irritation

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.

Comparative Clinical and Electrometric Assessments of the Impact of Surfactants on Forearm Skin

Surfactant-based skin care products can induce minimal to severer alterations of the human stratum corneum (SC). These changes can be conveniently assessed using electrometric devices. Four different surfactant-based solutions were applied to the forearms of 10 healthy volunteers following a soap chamber test method. The 2-day patch testing was followed by a 2-week follow-up. Clinical and instrumental assessments were performed at 7 time points. Data generated by the Corneometer® CM820, the Dermalab Moisture Module® and the Nova Dermal Phase Meter® (DPM) 9003 were compared. The significant differences between the product aggressiveness to the SC were similarly disclosed by the Corneometer and the Dermalab Moisture Module. The ranking of product aggressiveness given by the 3 devices 5 days after patch removal was similar to that given by the clinical assessment of erythema. A high level of correlation was found between the values yielded by the immediate and continuous mode assessments using the Dermalab Moisture Module with the pin probe, while the correlation was weaker with the Nova DPM. This finding may be related to the fact that the Nova DPM is influenced by the accumulation of the transepidermal water loss in the continuous mode assessment while there is no significant occlusion effect of the Dermalab Moisture pin probe that is more representative of the initial level of SC hydration. In conclusion, the Corneometer and the Dermalab Moisture Module respond similarly to changes in the SC content. This finding is different from some previous reports.