Didier Saint-Leger

How Does Sodium Lauryl Sulfate Alter the Skin Barrier Function in Man? A Multiparametric Approach

The effects of topically applied sodium lauryl sulfate were studied in vivo, in man, through noninvasive methods and compared with those obtained in vitro, using human stratum corneum as a model. The results show that the very marked increase of transepidermal water loss obtained in vivo cannot be related to any removal of epidermal lipids. The most likely explanation of our findings lies in the hyperhydration of stratum corneum consecutive to the inflammation process and a possible disorganization of the lipid bilayers.

Androgenetic alopecia and microinflammation

Today, androgenetic alopecia (AGA) is considered to be an alteration of hair growth and/or a premature aging of the pilosebaceous unit with a multifactorial and even polygenic etiology.1 The fact that the success rate of treatment with either antihypertensive agents, or modulators of androgen metabolism, barely exceeds 30% means that other pathways may be envisioned. The implication of various activators of inflammation in the etiology of AGA has progressively and recently emerged from several independent studies.2–11 A fibroplasia of the dermal sheath, which surrounds the hair follicle, is now suspected to be a common terminal process resulting in theminiaturization and involution of the pilosebaceous unit in AGA.2–8 We review here several observations underlining the possible implication of a slow, silent, and painless process in AGA. Because we think that it should not be confused with a classical inflammatory process, we have called it microinflammation. An early study referred to an inflammatory infiltrate of mononuclear cells and lymphocytes in about 50% of the scalp samples studied.2 Another more recent study by Jaworsky et al.3 confirmed an inflammatory infiltrate of activated T cells and macrophages in the upper third of the hair follicles from transitional regions of alopecia (i.e. which are characterized by actively progressing alopecia). This study also reported the occurrence of a developing fibrosis of the perifollicular sheath, together with the degranulation of follicular adventitial mast cells. The miniaturization of the hair follicles was found to be associated with a deposit of so-called ‘‘collagen or connective tissue streamers’’ beneath the follicle,2,7 as well as a 2–2.5 times enlargement of the follicular dermal sheath composed of densely packed collagen bundles.3 This thickening of the dermal sheath in progression zones of AGA has also recently been observed in our laboratory using immunohistochemical staining (Fig. 1). Horizontal section studies of scalp biopsies indicate that the so-called perifollicular fibrosis is generally mild, consisting of loose, concentric layers of fibrotic collagen that must be distinguished from cicatricial alopecia.4 It is unclear whether or not the fibrosis seen in follicular streamers (stelae or fibrous tracts) is permanent and/or alters the downgrowth of anagen hair follicles. Only 55% of male pattern AGA patients with microinflammation had hair regrowth in response to minoxidil treatment, which was less than the 77% of patients with no signs of inflammation,4 suggesting that, to some extent, perifollicular microinflammation may account for some cases of male pattern AGA which do not respond to minoxidil.4 Another study on 412 patients (193 men and 219 women) confirmed the presence of a significant degree of inflammation and fibrosis in at least 37% of AGA cases.5 The upper location of the infiltrate near the infrainfundibulum2–7 clearly distinguishes AGA from alopecia areata (AA), the latter disease being characterized by infiltrates in the bulb and dermal papilla zone.12 The aim of this review is to determine the location and chronology of the microinflammation process within the complex pathophysiology of the human pilosebaceous unit in order to improve the possible approaches for the reduction or prevention of the development of AGA.

Worldwide diversity of hair curliness: a new method of assessment.

Background  For many years, cosmetic scientists have attempted to measure the physical features of human hair, such as its shape and colour, as these can be artificially modified using cosmetic products. With regard to hair shape, previous anthropologic studies have emphasized its variability within and between human ethnic groups. Many studies have broadly distinguished three ethnic human subgroups: African, Asian, and Caucasian. Such a broad classification cannot account for the great complexity of human biological diversity, resulting from multiple, past or recent mixed origins. The verbal description of hair shape ranges from the classic to the more sophisticated, with terms such as straight, wavy, curly, frizzy, kinky, woolly, helical, etc. Although these descriptions evoke a global appearance, they remain confusing as their definitions and limits are unclear. Assessments are therefore required to more accurately define such verbal attributes.

Shape Variability and Classification of Human Hair: A Worldwide Approach

ABSTRACT Human hair has been commonly classified according to three conventional ethnic human subgroups, that is, African, Asian, and European. Such broad classification hardly accounts for the high complexity of human biological diversity, resulting from both multiple and past or recent mixed origins. The research reported here is intended to develop a more factual and scientific approach based on physical features of human hair. The aim of the study is dual: (1) to define hair types according to specific shape criteria through objective and simple measurements taken on hairs from 1,442 subjects from 18 different countries and (2) to define such hair types without referring to human ethnicity. The driving principle is simple: Because hair can be found in many different human subgroups, defining a straight or a curly hair should provide a more objective approach than a debatable ethnicity-based classification. The proposed method is simple to use and requires the measurement of only three easily accessible descriptors of hair shape: curve diameter (CD), curl index (i), and number of waves (w). This method leads to a worldwide coherent classification of hair in eight well-defined categories. The new hair categories, as described, should be more appropriate and more reliable than conventional standards in cosmetic and forensic sciences. Furthermore, the classification can be useful for testing whether hair shape diversity follows the continuous geographic and historical pattern suggested for human genetic variation or presents major discontinuities between some large human subdivisions, as claimed by earlier classical anthropology.

Comparison of the Kinetics of Sebum Secretion in Young Women with and without Acne

We utilized a sebum-sensitive adhesive film, Sebutape, to visualize the pore patterns of women with and without acne with computerized image analysis. In normal young women, we found a positive correlation between the number of active sebaceous follicles and total sebum excretion. When seborrhea was intense, this correlation was however lost. The situation was more complex in acne. The severity of seborrhea was positively correlated with the mean sebum excretion of individual follicles but not with the number of active follicles.

The use of hydroxy acids on the skin: characteristics of C8-lipohydroxy acid.

The hydroxy acids are widely used in skin creams because of their exfoliating and rejuvenating effect on photoaged skin. As a member of this family, the salicylic acid derivative known in the literature as 2‐hydroxy‐5‐octanoyl benzoic acid or β‐lipohydroxy acid has also been proposed as an exfoliant and as a treatment of photoaged skin and acne. This article reviews the effects of the hydroxy acids and compares them to those of the salicylic acid derivative. We propose the name C8‐lipohydroxy acid (C8‐LHA) for this derivative to differentiate it from other related compounds. The lipophilic nature of C8‐LHA and its relatively slow penetration in the skin afford it an exfoliating effect that is efficient at low concentrations. It appears to have antimicrobial, anti‐inflammatory, and anticomedogenic properties, which make it effective against acne. Its antifungal and exfoliating properties are also likely to prove useful in combating dandruff.

Chronological ageing of human hair keratin fibres

Examination of very long hair (length > 2.4 m) using a large range of evaluation methods including physical, chemical, biochemical and microscopic techniques has enabled to attain a detailed understanding of natural ageing of human hair keratin fibres. Scrutinizing hair that has undergone little or no oxidative aggression – because of the absence of action of chemical agents such as bleaching or dyeing – from the root to the tip shows the deterioration process, which gradually takes place from the outside to the inside of the hair shaft: first, a progressive abrasion of the cuticle, whilst the cortex structure remains unaltered, is evidenced along a length of roughly 1 m onwards together with constant shine, hydrophobicity and friction characteristics. Further along the fibre, a significant damage to cuticle scales occurs, which correlates well with ceramides and 18‐Methyl Eicosanoic Acid (18‐MEA) decline, and progressive decrease in keratin‐associated protein content. Most physical descriptors of mechanical and optical properties decay significantly. This detailed description of natural ageing of human hair fibres by a fine analysis of hair components and physical parameters in relationship with cosmetic characteristics provides a time‐dependent ‘damage scale’ of human hair, which may help in designing new targeted hair care formulations.

Relationships between hair growth rate and morphological parameters of human straight hair: a same law above ethnical origins?

After measurement of individual growth rates, natural hair fibres from Asian and Caucasian subjects were analysed using scanning electron microscopy. In total, more than 1000 hairs were analysed. Measurements of diameter, medulla and interscale distance (average distance between two successive cuticle scales) show these parameters strongly correlated with hair growth rate. A thicker hair fibre corresponds to a faster growth rate, a shorter interscale distance and greater probability to have a medulla, and vice versa, a thin hair fibre shows slower growth rate, a larger interscale distance and a lower probability to have a medulla. Very interestingly, this finding appears to be unrelated to the ethnic origin of the subjects, suggesting a common characteristic of human hair, at least for the straight or semi‐straight hair studied. From a practical viewpoint, this finding clearly suggests an alternative method for measuring hair growth rates, by measuring the interscale distance, which appears easier than using common laboratory equipments.

Isolation and identification of human hair ceramides.

The analysis of the lipids extracted from human hair by silica‐gel‐column liquid chromatography permitted an isolation of the fraction enriched in free ceramides. These were identified by GC/MS and are related to ceramide classes 2 and 5 in which the long‐chain base was predominantly sphinganine. This differs from that observed in the free ceramides found within the stratum corenum.

Effect of topical corticosteroids on human sebum production assessed by two different methods

SummaryTopical corticosteroids are widely used in cutaneous diseases. Although their mode of action on different skin compartments has been documented, little is known about their effects on the human sebaceous gland. We investigated the effects of two corticosteroids of differing potency on the excretion of sebum by means of two validated techniques: the Sebutape and the Lipometre. This study was conducted on the forehead skin of normal healthy subjects. The results obtained with both techniques correlated well. The application of both corticosteroids during a 4-week period led to a significant decrease in sebum excretion. This decrease was more pronounced with the more potent corticosteroid (Dermovate). In the light of these findings, it is likely that topical corticosteroÏds exert an anti-proliferative action upon the sebaceous cells in a similar manner to their effect in other skin compartments