International Journal of Cosmetic Science20, 53–61 (1998)
Surfactants and the skin
P. D Y K E S
Cutest Systems Ltd, 174, Whitchurch Road, Heath, Cardiff, CF4 3NB, UK
Clinical Scientist, Department of Dermatology, UNCH, Heath, Cardiff, CF4 4XN, UK
Prented at the SCS Symposium, Bristol, 7–8 April 1997
Received 4 April 1997
Accepted 23 September 1997
Keywords: surfactant; irritant dermatitis; stratum corneum; sodium lauryl sulphate; soap chamber test; tranpidermal water loss
Synopsis
The skin surface is the interface between us, the organism, and the outside world. When we clean the skin we remove not only the bacteria, dirt and grea which have accumulated, but also part of our natural barrier – the stratum corneum. Corneocytes, both singly and in clumps, are relead from the skin surface by the action of detergents and mechanical stimulation. So too are the lipids and proteins which make up the intercorneocyte region of the stratum corneum. The analysis of the types and amounts of materials relead by a standard scrub procedure may prove uful in the lection of surfactants with particular properties. Changes in the physical properties of the skin occur after washing. For example, changes in skin surface pH and tranpidermal water loss (a nsitive index of barrier function) are easily demonstrable. Excessive exposure to surfactants results in repeated damage to the stratum corneum which can in turn lead to an irritant dermatitis. Individual susceptibility to irritant dermatitis varies and this may be demonstrated using a simple patch test technique. This test is a way of potentially increasing the nsitivity of human bad assays such as the soap chamber test by prelection of subjects. Alternatively it may be possible to u measurements of function such as tranpidermal water loss or lar Doppler blood flow as an index of damage rather than conventional cutaneous irritancy. The approaches may help in the arch for the ideal of a non-irritant cleanr.
R´e sum´e
La surface de la peau est l’interface entre nous, notre organisme, et le monde ext´e rieur. Lorsque nous nettoyons notre peau nous ´e liminons non ulement les bact´e ries, la poussi`e re et la grais qui sont accumul´e es, mais aussi une partie de notre barri`e re naturelle, l’´e piderme. Des corn´e ocytes, que ce soit uls ou en pellicules, sont lib´e r´e s de la surface de la peau par l’action des d´e tergents et de la stimulation m´e canique. Le sont aussi les lipides et prot´e ines qui remplisnt la zone intercorn´e ocytaire de l’´e piderme. L’analy des types et des quantit´e s des mat´e riels relˆa ch´e s par unde proc´e dure standard de nettoyage peut s’av´e rer utile dans la s´e lection de tensioactifs ayant des propri´e t´e s particuli`e res. Des modifications des propri´e t´e s physiques de la peau interviennent apr`e s le lavage. Par exemple, des modifications dans le pH de la surface de la peau et la perte d’eau trans´e pidermique (indicateur nsible de la fonction de barri`e re) sont facilement mis en ´e vidence. Une exposition excessive aux tensioactifs conduit `a des dommages r´e p´e t´e s de l’´e piderme qui peuvent `a leur tour mener `a une dermatite irritante. La susceptibilit´e individuelle `a la dermatite irritante varie et on peut le d´e montrer en utilisant une technique de simple test par patch. Ce test est une façon d’augmenter potentiellement la nsibilit´e d’essais sur l’homme tels que le test de la cuve `a savon par pr´e s´e lection de sujets. D’une autre façon, il peut ˆe tre possible d’utilir des mesures de param`e tres tels que la perte d’eau trans´e pidermique ou le flux sanguin par lar Doppler, comme indices des dommages plutˆo t que l’irritabili
鬼谷子七十二术李白有什么之称t´e cutan´e e conventionnelle. Ces approches peuvent aider dans la recherche de l’id´e al du nettoyant non irritant.
0142–5463©1998 International Journal of Cosmetic Science
54Dykes Introduction
The skin surface is the interface between us, the organism, and the outside world. As such it becomes soiled by extraneous particulate matter, microorganisms, bodily cretions and excretions. The need to be regularly removed from the skin surface, although the need is partly biological and partly cultural. Biologically it would be reasonable to expect that regular removal of microorganisms would reduce the risk of skin infection. There may also be other biological aspects of skin cleansing including the need for regular stimulation of the nsory nerves of the skin. Culturally we need to be clean and odour free, although this need varies in different cultures and historically was not always so. It is alleged that when Napoleon was about to visit Jophine he would nd her specific instructions not to wash! In Elizabethan times a bath was something of an annual event. Fortunately we live in more odour-free times and the skin surface is usually subjected to application of a cleansing agent at least once daily. Removal of the unwanted surface material requires that the clea
nsing agent has veral properties. First, it must wet the naturally water repellent skin surface. Secondly, it must solubilize or emulsify and remove surface debris, including some of the stratum corneum. Thirdly is must do the things without causing harm to the skin. Unfortunately this is an almost impossible dilemma to overcome and the cleansing process, if repeated regularly, may lead to cutaneous irritant reactions.
参商歌词Skin surface
The epidermis is the outermost layer of skin and its main function is to produce the stratum corneum, our interface with the outside world. The stratum corneum consists of individual cells called corneocytes embedded in a lipid rich matrix in an arrangement akin to a brick wall. To produce the stratum corneum, the epidermis must undergo a complex process termed keratinization [1]. Many biochemically different molecules and mechanisms are involved in the process by which a viable epidermal cell is converted into a flattened, shield like, anucleated corneocyte. Keratins are central to the process of keratinization and form the bulk of the centre of the corneocyte. Surrounding the corneocyte is a tough cross-linked cell envelope which helps give the stratum corneum its rigidity and chemical resistivity.
流水人家
It must be remembered that the epidermis is a dynamic structure and in the normal situation renews itlf approximately every 30 days. There is therefore a constant movement of cells outwards and a continuous but imperceptible loss of corneocytes from the skin surface. It is only when we deliberately cover the skin surface, such as when a limb is plastered following a break, that a build up of scale occurs and we become aware of this process. The outward movement of cells may have evolved as a defence mechanism to prevent large scale colonization by infectious agents. Regular removal of the surface corneocytes by cleansing could rve as a stimulus to epidermal growth and differentiation and therefore aid this function.望庐山瀑布作者
As well as the products of keratinization, other materials are prent on the skin surface. At certain body sites, for example, the face and back, the skin appears greasy and this is due to the output of bum from the dermal baceous glands which are common is the acne-prone areas. Another dermal gland, the apocrine gland also discharges onto the skin surface but this gland is restricted mainly to the axillae and groin areas. Commensals such as bacteria and yeasts are also prent at various body sites particularly the face, axillae and groin. Bacteria, by their actions on baceous and apocrine cretions, contribute
significantly to body odour. Sweat residues are also prent on the skin surface at many body sites a
nd may also be the subject of bacterial action. The longer the interval between washing the greater the changes induced by the bacteria and the greater the odour problem.
When we clean the skin we produce changes in the skin surface which range from removal of bacteria and grea to imperceptible biochemical changes in the stratum corneum to removal of corneocytes. This process, if repeated frequently, results in irritant skin reactions in some individuals. The reactions may be transient in nature or, if the stimulus is prolonged, may give ri to chronic conditions such as hand eczema, or ‘houwives dermatitis’.
Action of surfactants
If viewed microscopically, the most obvious feature of skin surface washings, are the corneocytes both singly and in clumps. Different detergents lead to the relea of different amounts of corneocytes. This can be demonstrated by using a simple scrub device consisting of a rotating perspex blade in a cylindrical chamber [2]. In the prence of a known volume of liquid containing a detergent, the blade is rotated at a fixed speed and pressure for a predetermined time. In an experiment using the scrub device, 12 volunteer subjects were tested with two wash products A and B. The results shown in Fig. 1 clearly show the enhanced relea of corneocytes compared to the bu
ffer alone control and also differences between the two wash products. In a human irritation assay B scored more highly than A, but with the limited data it is not possible to say that there is a direct relationship between the number of corneocytes relead and irritation potential.
走进西柏坡In the same experiment the amount of stratum corneum protein solubilized was also measured. The results, shown in Fig. 2, indicate that wash product A solubilized far more protein than B. Clearly the amount of protein relead does not correlate with the number
of corneocytes relead nor for that matter with the irritancy potential.
Figure 1.Mean number of corneocytes relead by the scrub device in the prence of two wash products (A and B) and a control without detergent in 12 volunteer subjects.
55Surfactants and the skin
In a parate experiment we have examined the types of lipid relead by the action of a surfactant on the skin [3]. In this study Triton X100 was ud and the washings extracted by using the standard Folch extraction procedure (chloroform/methanol ϭ2:1). Individual lipid class were estimated quantitatively by thin layer chromatography followed by flame ionization detection. Comparisons were made with the Folch extractions of whole stratum corneum. The results, shown in Fig. 3, indicate that a greater percentage of hydrophilic lipids, such as triglycerides and free fatty acids, are relead in preference to the more hydrophobic lipids such as ceramides. Interestingly it has been reported that a proclivity to surfactant-induced irritation is related to low levels of ceramides in the stratum corneum [4].
Surfactant induced changes
It is perhaps not surprising that in view of the above obrvations, washing can lead to changes in some basic properties of the skin surface. Two important ones as far as surfactants are concerned are the skin surface pH and the barrier function of the skin as measured by tranpidermal water loss (TEWL).
The skin’s surface is naturally acidic, ranging from pH 4 to pH 6. This is in contrast to the pH of the internal environment of near neutrality (pH 7.2–7.5). It is generally believed that this change in pH is a result of the production of certain amino acids and lactic acid by the epidermis combined with the acidic substances in sweat and bum. This ‘acid mantle’ may be important in preventing microbial and fungal infections. U of soaps and detergents in general leads to increas in pH, i.e. the skin becomes more alkaline [5].However the degree of change and the time to recovery does vary with different products.In a parate study, Korting et al
. [6] showed clearly that the increa in pH after repeated Figure 2.Mean concentration of stratum corneum protein relead by the scrub device in the prence of two wash products (A and B) and a control without detergent in 12volunteer subjects.
56Dykes
高尔夫的起源
washing with a soap bar was associated with an increa in Propionibacterium acnes , a commensal implicated as a causative factor in acne. In contrast, the smaller increa in pH obrved with a detergent bar was not associated with incread bacterial numbers.
It is generally assumed that the greater the change in pH induced by a soap or surfactant,the more irritant the product. However the importance of pH has been questioned [7,8] and other factors have therefore to be considered. For example, skin compromid by low level exposure to surfactant is more susceptible to other chemical irritants [9]. The irritancy potential of a surfactant may therefore be due to synergism between different factors.Tranpidermal water loss (TEWL) is a measure of the barrier function of the skin and is a nsitive index of damage to that barrier. Prolonged contact (24h) under occlusion with surfactants such as sodium lauryl sulphate leads to cutaneous inflammation with incread TEWL [10]. Perhaps more relevant to the u of products containing sur
factants,is the fact that increas in TEWL can be demonstrated after single washes with further increas after repetitive washes [11]. The nature of the changes is not clear but undoubtedly involves the initial interaction of surfactant with the intercellular lipids of the stratum corneum leading to penetration of the surfactant into the viable epidermal cell layer underneath. The surfactant can then cau cell damage or even cell lysis with the development of a clinically obvious irritant reaction.
九寨沟的春天Surfactants and dermatitis
Excessive exposure to surfactants often leads to cutaneous irritant reactions such as hand dermatitis. Clinically the reactions are typified by erythema (redness) and scaliness (cracking and fissuring in extreme cas). Other less obvious symptoms of surfactant damage include dryness and tightness, which can be a problem particularly on the face.The incidence of adver reactions to surfactants in the community is difficult to judge.
One survey on the adver effects of cosmetics and toiletries indicated that in females Figure 3.Percentage composition of Triton X-100-extracted lipid (ᮀ) compared to whole
stratum corneum lipid (ٗ
րր).57
Surfactants and the skin
