The prevention of actinic damage has become

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1 Protection from visible light by commonly used textiles is not predicted by ultraviolet protection Caroline Van den Keybus, MD, a Jan Laperre, PhD, b and Rik Roelandts, MD, PhD a Leuven and Zwijnaarde, Belgium Interest is increasing in the prevention of acute and chronic actinic damage provided by clothing. This interest has focused mainly on protection against ultraviolet irradiation, but it has now also turned to protection against visible light. This change is mainly due to the action spectrum in the visible light range of some photodermatoses and the increasing interest in photodynamic therapy. The ultraviolet protection provided by commercially available textiles can be graded by determining an ultraviolet protection factor. Several methods have already been used to determine the ultraviolet protection factor. The fact that protection from visible light by textiles cannot be predicted by their ultraviolet protection makes the situation more complicated. This study attempts to determine whether or not the ultraviolet protection factor value of a particular textile is a good parameter for gauging its protection in the visible light range and concludes that a protection factor of textile materials against visible light needs to be developed. This development should go beyond the protection factor definition used in this article, which has some limitations, and should take into account the exact action spectrum for which the protection is needed. ( J Am Acad Dermatol 2006;54:86-93.) The prevention of actinic damage has become increasingly important in recent years. The change in sun exposure habits over the past few decades has increased the incidence of a variety of photodermatoses, skin aging, and skin cancer. Not only is the incidence of skin cancer increasing, but the age at which first symptoms appear is decreasing, which is even more frightening. Because of the long interval between the sun exposure and the development of skin cancer, a higher increase may be expected in the future. Therefore adequate sun protection is becoming even more necessary. Up to quite recently, sun protection was considered mainly a matter of use of sunscreens. However, the use of broad-spectrum sunscreens with high sun protection factor (SPF) values often resulted in people exposing their skin much longer to the damaging From the Photodermatology Unit, University Hospital, Leuven, a and Scientific and Technical Centre of the Belgian Textile Industry, Centexbel, Zwijnaarde. b Funding sources: None. Conflicts of interest: None identified. Accepted for publication August 30, Reprint requests: Rik Roelandts, MD, PhD, Department of Dermatology, Photodermatology Unit, University Hospital, Kapucijnenvoer 33, B-3000, Leuven, Belgium. Rik. Roelandts@uz.kuleuven.ac.be. Published online November 15, /$32.00 ª 2005 by the American Academy of Dermatology, Inc. doi: /j.jaad Abbreviations used: ALA: aminolevulinic acid SPF: sun protection factor UPF: ultraviolet protection factor UV: ultraviolet : protection factor for visible light effects of sun exposure, the precise opposite of the intended effect. 1 Therefore sun protection by textiles has become more and more important because it can provide better protection than sunscreens. Clothing fabrics have been proposed in the treatment of photosensitive patients 2,3 as well as for protection against xeroderma pigmentosum 4 and premalignant lesions. 5,6 Clothing can be labeled with a protection factor in the ultraviolet (UV) range (ultraviolet protection factor; UPF), 7,8 in the same way as the SPF for sunscreens. Different methods have been used. 2-5,7,9-11 Commercial summer fabrics, however, frequently provide insufficient UV protection. 12 Labeling is already available in Australia, New Zealand, Europe, the United States, and Canada, although this may vary from one country to another. In Australia, the measured UPF is marked if the UPF is between 15 and In the United States, the test method for determining the UPF was developed by the American Association of Textile Chemists and Colorists. 14 The classification and labeling of clothing follows the Australian classification system. 15 In 86

2 JAM ACAD DERMATOL VOLUME 54, NUMBER 1 Van den Keybus, Laperre, and Roelandts 87 Europe, clothing can bear a UV-protective label only if the UPF is higher than 40 and if, at the same time, UVA transmission is less than 5%. A UPF of 401 seems to be sufficient even in extreme exposure situations. 16 The European standard further specifies clothing design requirements such that as much skin as possible is covered. 17,18 In general, in vivo methods (eg, erythemaresponse methods) produce lower UPF values than do in vitro methods (eg, transmission measurements). 11,19,20 Not only the method used but also environmental factors such as wetness may increase or decrease the UPF depending on the fabric. 19,21,22 Indeed, even everyday use may improve the UPF of pure cotton, at least in the short term. 23 The addition of UV absorbers, optical brightening agents, and dyes may also alter the degree of protection. In the meantime, industry is increasing the research into UV protective textiles in the effort to improve this protection. There is also a growing awareness on the part of consumer organizations. Textiles offer protection against visible light, a spectrum for which sunscreens offer much less protection than for UV light. Some photosensitive patients have an action spectrum in the visible light range. In addition, visible light sources are used for photodynamic therapy for precancerous lesions or superficial skin cancers, so it may also be wise to protect the skin against visible light. When protection in the visible light range becomes important, this protection needs to be evaluated. Only a few such studies have been done. 24 The purpose of this study is to evaluate the protection of textile materials against visible light and to determine whether the UPF used to grade the protection in the UVrange is also a valid parameter for the classification of protection in the visible light range. MATERIAL AND METHODS Fabrics Thirty-four different textiles, suitable for summer clothing, were evaluated for the protection they provided against visible light after a UPF had been determined for each of them. The series contains cellulosic materials (eg, cotton, viscose, flax) and synthetic materials of various kinds (eg, acrylic, polyester, polypropylene). The materials, either woven or knitted, were all plain materials. The composition, color, density, and structure of the materials are given in Table I. Determination of the UPF The UPF was determined according to the European Committee for Standardization Norm EN using the following formula 17 : EðlÞSðlÞDðlÞ 290 UPF ¼ EðlÞSðlÞTðlÞDðlÞ 290 where E(l) is the irradiance of the sun expressed in watts per nanometer per square meter; S(l) is erythema action spectrum; D(l) is the bandwidth; and T(l) is the transmission coefficient of the material, as determined by the relation between the intensity of the transmitted radiation to the intensity of the incident radiation. Since S(l), E(l), and D(l) are known, the UPF can be calculated by means of the transmission coefficient T(l). The transmission percentage of the radiation was measured with a spectrometer. Normal incident monochromatic radiation was used in combination with collection of radiation from an integrating sphere (UV/VIS/NIR PerkinElmer Lambda 900; PerkinElmer, Boston, Mass) to measure direct and diffuse radiation simultaneously. A UG11 Schott filter of 2-mm thickness (Schott, Mainz, Germany) was used between the sample and the integrating sphere to minimize the fluorescence that could be induced by the optical brightening agents. Fluorescence emission could increase the transmission and thus lead to underestimating the UPF. Approximately 90% of all white materials contain optical brightening agents, which have fluorescent characteristics. They absorb radiation around 350 to 360 nm and re-emit these rays at higher wavelengths, namely 400 to 430 nm. With this absorption, they have a favorable effect on the UPF. Determination of the visible-light protection factor To determine the protection factor of the textile materials at a particular wavelength in the visible light range, two methods were used. In the first method a 900-W xenon lamp was used in combination with a monochromator (Applied Photophysics, London, UK). The transmission was measured at different wavelengths in the visible light range: 400, 450, 500, 550, 600, 650, and 700 nm. The bandwidth for each of these wavelengths was 32 nm. The intensity was measured with a thermopile. The transmission was determined by comparing the intensity at each wavelength through the textile sample and without the textile sample (the control). The second method used a spectrophotometer equipped with an integrating sphere. The light generated by a xenon source passes through a monochromator with a bandwidth of 1 nm and impinges perpendicular to the sample. The sample is positioned in front of the integrating sphere for collection

3 88 Van den Keybus, Laperre, and Roelandts JAM ACAD DERMATOL JANUARY 2006 Table I. Characteristics of the tested materials No. Composition Color Density (g/m 2 ) Structure UPF* 400 nm 450 nm 500 nm 550 nm 600 nm 650 nm 700 nm % cotton Ecru 193 Woven % cotton Ecru 296 Woven % cotton Marine 256 Knit % cotton White 260 Knit % cotton Green 260 Knit % cotton Blue 188 Knit % cotton White 184 Knit % cotton Blue 208 Knit % cotton Light green 472 Woven? % acrylic fiber White 204 Woven % acrylic fiber White 262 Woven % acrylic fiber White 175 Woven % acrylic fiber White 270 Woven % acrylic fiber White 243 Woven % acrylic fiber White 207 Woven % acrylic fiber White 303 Woven % polyester White 114 Woven % polyester White 192 Woven % polyester White 116 Woven % polypropylene White 185 Woven % polypropylene White 202 Woven % polypropylene White 249 Woven % polypropylene White 201 Woven % cotton 50% White 252 Knit modal 25 50% cotton 50% Blue 252 Knit modal 26 50% cotton 50% Yellow 280 Knit modal 27 Viscose/flax Khaki 183 Woven Cotton/flax White 106 Woven Flax Ecru 100 Woven Flax Ecru 110 Woven Flax Ecru 192 Woven Flax Ecru 190 Woven Flax Ecru 105 Woven Flax Ecru 129 Woven Polyester Pastel green 57 Woven Polyester Light green 57 Woven Polyester Dark green 57 Woven *UPF and as determined with a xenon lamp in combination with a monochromator at different wavelengths. of direct and diffuse transmitted radiation. The wavelength step used was 1 nm. On the basis of this transmission, a protection factor for visible light () was determined as follows, where T(l), the transmission coefficient, is at a particular wavelength: ðlþ¼ 1 TðlÞ RESULTS As shown in Table I, the protection offered by textiles in the visible light range is, in general, better for shorter than longer wavelengths. This can be partly explained by the better penetration of the longer wavelengths as compared with the shorter ones. However, this may vary from one material to another because of several factors. Influence of the density of the material on the transmission of visible radiation For a given color and a given textile, the density of the material inversely influences the transmission of visible radiation, that is, an increase in density

4 JAM ACAD DERMATOL VOLUME 54, NUMBER 1 Van den Keybus, Laperre, and Roelandts 89 Fig 1. Cover factor as a function of ratio of yarn thickness and length of repeat for a simple material. results in a decrease in transmission. The density of a material is increased by either increasing the yarn count (the linear mass of the yarn) or by increasing the yarn density (the number of yarns per unit length). This increase results in an increase in the cover factor and subsequently in a decrease of the transmission of visible radiation. The higher the cover factor, the more textile material is present in a unit cell. The cover factor for a simple material for a given dimension of warped weft yarns is plotted as a function of the ratio of the yarn thickness and the length of the repeat (Fig 1). The repeat is a unit cell describing the way yarns in warp and weft direction are arranged. The figure represents the most simple way of arranging yarns and cannot be extrapolated to other more sophisticated repeats. In this simplified model it is clear that the cover factor first increases steeply but levels off with the yarn-thickness repeat ratio. This leveling off is observed for each wavelength tested. Influence of color of the textile material on transmission of visible radiation The higher the cover factor, the more important becomes the polymer type of which the textile yarns are composed and the chemicals carried by the yarns, such as the dye, which generates the color and other chemicals that may be present. Together with the polymer composition, the dye determines the color and thus affects the transmission. Color is an important parameter for the reflection and transmission of visual radiation. The coloration of textiles is obtained by the incorporation of dye molecules in the fibers. Dyes are organic compounds that are able to selectively absorb and reflect visible radiation. A dye must have conjugated double bonds. In this structure, specific groups are present that are called chromophores, which provide Fig 2. Influence of color on in materials with same structure (50% cotton and 50% modal) and density. Sample 24 is white, sample 25 is blue, and sample 26 is yellow (see Table I). the color, and auxochromes, which intensify and deepen the color by increasing the absorption maximum. 25 The color of a fabric is determined by the wavelengths it reflects, and this reflection in specific wavelength regions produces color. The importance of color in the protection against visible light is illustrated in Fig 2, where the is given for 3 different colors of the same fabric containing 50% cotton and 50% modal (Viscose, a man-made cellulose fiber) with the same structure and density. The white sample offers only feeble protection over the entire visible light range. The yellow sample has an absorption peak at 400 nm and absorbs the blue light, whereas the other wavelengths combine to form yellow. If red is also removed, then the color turns to green. The blue sample has an absorption peak at 600 nm and absorbs the yellow light, so the other wavelengths combine to form blue. As shown in Table I, white fabrics, in general, do not offer high protection over the entire visible light range. It is, however, very difficult to predict which wavelength regions the dye will absorb and how much for a particular color. In general, darker colors absorb more than lighter colors. This is shown in Fig 3 in which transmission spectra are given for a polyester fabric dyed in different grades of green. The wavelength dependency of the transmission of darker colored fabrics is clearly lower than for lighter colored fabrics. At 700 nm, however, the protection offered by the light green material is higher than the protection offered by the dark and pastel green material. Relationship between UPF and To determine which fabrics should be advised for protection in the visible light range, the s for a

5 90 Van den Keybus, Laperre, and Roelandts JAM ACAD DERMATOL JANUARY 2006 Fig 3. Transmission spectra for polyester fabric dyed in different grades of green. All materials are 100% polyester and weigh 57g/m 2. They are woven materials with 48 threads/cm in the warp (direction of production of a woven textile material) and 28 threads/cm in the weft (direction perpendicular to production direction of a woven textile material). UPF of these fabrics is 14.8 for the pastel green sample (No. 35), 20.6 for the light green sample (No. 36), and 24.0 for the dark green sample (No. 37) (see Table I). series of fabrics were compared at 400 and 600 nm. In addition, these values were compared with the fabric s UPFs to determine whether a fabric with a high UPF also offers adequate protection in the visible light range. The results seem to vary for the different materials. One has to be careful in comparing the with the UPF because the UPF is a composite, integrated metric, whereas the, as defined in this study, is always a function of the wavelength. The first material that was evaluated is flax. For fabrics with a low cover factor and, consequently, a considerable degree of open spaces between the yarns, it can be expected that the degree of protection in the visible range is of the same degree as the protection in the UV range. This is illustrated by a series of ecru flax materials (Table I, Nos. 29, 30, 31, 32, 33, 34). The low protection they provide may be due to the type of raw material used, its low density, and its lack of dye. The role the type of raw material plays in the influencing of the UPF depends primarily on its chemical structure. The presence of many conjugated compounds will have a favorable effect on the UV absorption. 26 Flax is 80% cellulose, which has no double bonds in its chemical structure. Flax thus has a low intrinsic UV absorption capacity. The same is true for nylon, acryl, viscose, and cotton. In contrast, polyester is a synthetic material with double bonds in its chemical structure. Therefore it gives a good protection in the UV range, especially for wavelengths under 310 nm. 25 Fig 4. Increase in UPF and of flax at 400 nm as a function of density. In general, materials with a high density and thus a high degree of coverage have a high UPF. Some dyes absorb wavelengths in the UV spectrum so they are able to increase the UPF of textiles. Ecru materials have no dyes, so for ecru flax materials the difference in density determines the difference in permeability. In both UV and visible light, the protection factor increases with the increase in density (Fig 4). We evaluated not only flax but also other materials such as polyester, polypropylene, and acryl, which were all white. With these materials a clear difference is noted between the UPF and the. The UV protection factors of 100% acryl materials (Table I, Nos. 10, 11, 12, 13, 14, 15, 16) are slightly higher than the protection factors at 400 nm, which in their turn are higher than those at 600 nm. Because they are white and thus contain an optical brightening agent, they have some degree of UV absorption. Because of this absorption, the brightening agents will thus have a favorable effect on the UPF but not on the protection factor for visible light. Their effect is not so spectacular since the influence of the wavelengths between 350 and 360 nm is very little in comparison with that of 310 nm as far as erythema formation is concerned. 27 For the 100% polypropylene materials (Table I, Nos. 20, 21, 22, 23), there are several reasons for a higher degree of protection in the UV spectrum than in the visible-light spectrum. First, polypropylene, as already noted, is routinely given a UV absorber. Second, they are white and thus one can expect a limited effect of the optical bleaching agent. The higher degree of protection in the UV range than in visible light for 100% polyester materials (Table I, numbers 17, 18, 19) is due to the raw material itself and the white color. Polyester has a

6 JAM ACAD DERMATOL VOLUME 54, NUMBER 1 Van den Keybus, Laperre, and Roelandts 91 Table II. values of a common green terrycloth towel at different wavelengths Wavelength (nm) terrycloth towel Fig 5. Increase of UPF and of acrylic fabric at 400 nm as a function of density. conjugated structure, so it has good intrinsic UV absorption. The presence of an optical bleaching agent also somewhat enhances the UV absorption. The difference in density within one material class (polyester, polypropylene, or acryl materials) determines the difference in permeability. The increase in the protection factor with increasing density, however, is more pronounced in the UV spectrum than for visible light (Fig 5). For white materials that have a higher density and are further identical, the UPF is higher than the because the absorbing effect of the optical bleaching agent in the UV range has more effect at a higher density. High-UPF as well as low- UPF materials provide little protection in visible light. A material with both a high UPF and a high density thus does not necessarily offer good protection in visible light. Only if a material with a high UPF is yellow will the patient be protected at 400 nm. Blue material will offer more protection at wavelengths around 600 nm. Protection against visible light in photodynamic therapy In the United States, the wavelengths emitted by most light sources used for photodynamic therapy in combination with 5-aminolevulinic acid (ALA) are between 400 and 420 nm. In Europe, red light (between 600 and 700 nm) is used for topical photodynamic therapy. When several skin areas treated with ALA have to be irradiated the same day, it may be necessary to protect already irradiated areas to prevent overlapping irradiation. In addition, protection against visible light is also important in the interval between application of the ALA and the irradiation. As has been already noted, the most protection is observed for materials with a high cover factor. Color or color depth should not be relied upon in the choice of a material, nor is it advisable to use a material with identical color as the color of the source because, in general, an increase in transmission is observed in this region. An ordinary terrycloth towel may have a very high cover factor because of the protruding yarns and its 3- dimensional structure. Table II gives an example of the values of a green, 100% cotton terrycloth towel with a fabric weight of 472 g/m 2 that was evaluated for its transmission in the visible light range at different wavelengths (400, 450, 500, 550, 600, 650, and 700 nm). As shown, the values between 400 and 700 nm are sufficiently high to avoid much transmittance at these wavelengths. DISCUSSION Several fabrics are available that can provide broad-spectrum sun protection, some with protection factors of more than The UPF has been proposed as a parameter for the UV protection of fabrics. 7-9 As with sunscreens, this protection factor will mainly indicate the degree of protection against UV(B). The main purpose herein has been to evaluate the protection against UV-induced erythema because UV-protecting fabrics have been promoted primarily as protection against sunburn for which the information provided by the UPF will be sufficient. However, there are many more reasons for the use of fabrics, such as to protect the skin against photoaging and skin cancer or to protect photosensitive patients. Because the action spectrum of these end points can also include UVA, such fabrics should also offer good UVA protection and therefore should be tested for the degree of UVA protection they provide. In the same way, protection against visible light can be of importance for patients with different types of porphyria, with chronic actinic dermatitis, or with solar urticaria with action spectrums in the visible light range. Patients receiving photodynamic therapy may also benefit from fabrics with protection in the visible light range. Our study has attempted to determine whether a fabric with a high UPF value could offer an adequate protection in the visible light range. The results vary

7 92 Van den Keybus, Laperre, and Roelandts JAM ACAD DERMATOL JANUARY 2006 according to the different materials of the fabric. In general and apart from flax, the UPF value is higher than the value of the materials tested. Even in the visible light range, there can be large differences for the same material depending on the wavelengths tested. In addition, the materials with the highest UPF values do not necessarily have the highest values. Therefore the UPF value is not a valuable parameter for evaluating protection in the visible light range, which suggests the need for a separate evaluation method. Although our study shows that some commercially available materials do offer very high protection in the visible light range, large differences in protection are noted from one material to another. If one needs information about the protection a particular fabric offers in the visible light range, it is advisable to determine a, which is comparable to the SPF of a sunscreen and the UPF of a fabric. There is, however, one main difference. For protection against erythema, one may propose a minimal SPF or a minimal UPF, which is much more difficult for a. Not enough data are available to predict the minimal needed to protect a patient with, for example, chronic actinic dermatitis or solar urticaria. Nor is it clear whether a of 20 at a particular wavelength will be sufficient to protect a patient with a photodermatosis. In addition, such patients can also be photosensitive to wavelengths other than visible light. Another problem is the large differences in photosensitivity from one patient to another for the same wavelength in the visible light range. In this respect, the main value of determining a will be to compare the protection in the visible light range provided by different fabrics in order to select those with the highest protection available at the wavelengths to which the patient is photosensitive. In addition, the material must be pleasant to wear in a particular situation, so that the patient will wear the clothing. Until now this aspect has been neglected too much. The main limitation of the conclusion is that the is not taking into account the action spectrum for the visible light. This action is spectrum is, to a large extent, unknown and varies significantly with the biological endpoint and skin type. For protection under 310 nm, polyester seems to be the preferable fabric. For the longer UV wavelengths, acryl, viscose, cotton, nylon, and flax offer mostly higher protection than polyester, although their UV protection is rather low. Color can also be important. 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