Photochemistry and Photobiology, 2014, 90: 1199–1206
New Advances in Protection Against Solar Ultraviolet Radiation in Textiles for Summer Clothing Aguilera*, Marıa Victoria de Ga lvez, Cristina Sa nchez-Rolda n and Enrique Herrera-Ceballos Jose Photobiological Dermatology Laboratory, Medical Research Centre, Department of Dermatology and Medicine, Faculty of Medicine, University of Malaga, Malaga, Spain Received 10 March 2014, accepted 14 May 2014, DOI: 10.1111/php.12292
ABSTRACT Clothing is considered one of the most important tools for photoprotection against harmful solar ultraviolet radiation (UVR). The standard for sun-protective clothing is based on erythema despite other biological effects of UVR on the skin. We analyzed the potential protection against UVR in fabrics destined for summer clothing based on several action spectra. We examined 50 garments classified by type of fabric composition, structure of the fiber yarn and color. The ultraviolet protection factor was calculated based on fabric ultraviolet transmittance corrected for erythema according to the EU standard E-13758 as well as the UVA transmittance of fabrics. UVR protection was also analyzed in base of different action spectra as for previtamin D3, nonmelanoma skin cancer, photoimmunosuppression and photoaging. Most knitted fabrics used for sports T-shirts offered excellent ratings for ultraviolet protection while normal shirts showed very low ratings, particularly against photoaging. The cover is the most influential variable in fabric photoprotection, having an exponential relationship with the UPF. The relation between cover and UVA protection was linearly negative. Information about ultraviolet protection in textiles used for summer clothing should be included in labeling as some types of fabrics, especially those used for shirts, offer very low UVR protection.
INTRODUCTION Several epidemiological studies have shown a significant increase in the incidence of diseases resulting from solar ultraviolet action. Reasons for this increase include an increased life expectancy, changes in lifestyle habits resulting in increased sun exposure (and its artificial alternative), the type of clothes worn, and in certain latitudes a decrease in the ozone layer. In Spain, photoprotection is one of the most important social objectives in the prevention of the risks incurred by sun exposure. This is related with the geographical situation of Spain in latitudes with more than 300 days of sunshine per year, and the associated national and international tourism. The incidence data of skin cancer are similar to those of other European Mediterranean countries. During the first decade of this century, the adjusted mean incidence per 100 000 habitants was 82.6 for basal cell *Corresponding author email: [email protected] (Jose Aguilera) © 2014 The American Society of Photobiology
carcinoma, 19.03 for squamous cell carcinoma and 6.7 for malignant melanoma (1). In view of these figures, primary prevention is seen as paramount to tackle the problem of skin cancer from the standpoint of public health. Accordingly, application of the standards on the degree of protection afforded by the various photoprotection methods (sunscreen, hats and sunglasses) is fundamental. These laws are now clearly disseminated and accepted in the community. Considerable interest has recently been given to the degree of solar protection afforded by fabrics. WHO and several photoprotection associations have recommended the protection by fabrics as the first line of defense against solar UV, in addition to the use of photoprotective creams, hats and glasses. This has led textile manufacturers to establish new lines of research and development in fibers, dyes, detergents and finished products to ensure the highest degree of photoprotection (2–5). Thus, as an information about the degree of protection provided by these fabrics needs to be given in a standardized form, different in vitro methods of study have been examined (6,7), methods that correlate perfectly with the in vivo protective measurements (7–9). Recently, the European Commission for Standardization (CEN) has developed and standardized the method for estimating protection offered by solar radiation fabrics in Europe (European standard EN 13758) (10,11). The method, based on in vitro measurements from the transmittance values of the fabric and corrected for the erythemal action spectrum determines the Ultraviolet Protection Factor (UPF) of textiles. A UPF value of 40 or higher has been determined to represent a sufficient level of fabric protection for extreme exposure in any location. This level also takes into account protection in situations of decreased fabric UPF values (e.g. stretching, moisture and washing) (11). Although it is generally considered that clothing provides sufficient protection against solar ultraviolet radiation, in many cases this may not be entirely the case. Even fabrics that a priori appear not to possess light transmittance are able to let significant amounts of ultraviolet radiation through, enough to produce erythema (12,13). In the case of fabrics with light textures, such as those used for summer clothes, the erythema risk is even higher (14). In latitudes like those of central and southern Spain, which have more than 300 days of sunshine per year, the mean erythemal irradiance at midday in summer reaches ultraviolet index values of 8–9 (15,16). Therefore, clothing should incorporate solar protection, at least that designed for summer wear and particularly that made for children, the elderly, professionals exposed to high solar doses and, if possible, photosensitive
1199
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patients. Herein lies one of the limitations in the standardization of ultraviolet protection offered by fabrics. Despite the existence of official standards based on erythema for ultraviolet protection of textiles, a series of biological effects take place in the skin after exposure to solar radiation that need to be considered for the complete evaluation of the photoprotection offered by fabrics, with special emphasis on UVA protection and such conditions as photoaging or skin photosensitivity. Yet many fabrics that provide good protection against sunburn may provide inadequate protection against photosensitization by the intrinsic or extrinsic absorbance of molecules or against (pre)malignant lesions. Patients with xeroderma pigmentosum or solar urticaria have been reported to experience typical lesions of the disease in areas covered by light-colored fabrics or areas of low coverage (17,18). The aim, therefore, of this study was to analyze the protection capability against solar ultraviolet radiation of various different fabrics used for summer clothing. We examined a set of biological action spectra depending on both the UVB and UVA region of the solar spectrum. Following EU standards, the UPF (based on erythema) as well as the UVA transmittance were analyzed in relation to textile composition, fiber structure and fabric color.
summer fabrics interesting given its extremely rapid market acceptance. Two main groups of clothing could be differentiated: woven shirts and weft-knit sports T-shirts. We considered the fabric used for technical sports T-shirts as knit fabric after image analysis of the yarn, despite the bilayer composition of this sweat-reducing fabric. Within each different type of fabric, we also analyzed the different colors to determine the degree of dye or pigment staining of the fabric with relation to its ability to filter ultraviolet radiation. The UPF was calculated according to the European standard for solar ultraviolet protective properties of fabrics (EN-13 758) (10). The calculation is based on estimating the solar ultraviolet radiation transmittance of the fabric at different wavelengths between 290 and 400 nm and corrected for its relative effectiveness at delaying erythema in human skin (from the CIE reference action spectrum) (19). Briefly, each fabric sample was placed on the sensor (Ulbrich sphere type) of a Macam SR-2210 double monochromator spectroradiometer (Macam, Scotland) and illuminated with a 300 W Oriel solar simulator (Oriel, Newport Corporation, Irvine, USA). The sample was spread evenly and without tension to avoid optical changes due to alterations in the geometry of the fabric. For each wavelength, the spectral irradiation was multiplied by its relative effectiveness at producing delayed erythema and by the transmittance value of the fabric. The UPF was calculated using the following formula:
MATERIALS AND METHODS
where UPF, ultraviolet protection factor; E, spectral irradiance; e, relative effectiveness for erythema; T, transmittance of the fabric. The UPF value was calculated from the arithmetic mean of the UPF of 5 independent samples of the same fabric. Following EU norms, the final UPF of the sample was obtained after statistical correction. The measurement error was subtracted from the mean UPF. This error was calculated from the standard deviation of the UPF for a confidence interval of 99%, given by the Student-t value. Thus, the UPF has a 99% probability of being the real UPF of the sample. The final UPF was calculated according to the following formula:
A total of 50 fabrics were analyzed, sorted by: textile type, use, composition and color (Table 1). From a practical standpoint, we examined a series of textiles mainly used for traditional clothing worn in summer. Microscopic analysis of the fabrics (Fig. 1) showed that each different type corresponds to a particular structure, yarn and composition. Thus, we were able to determine 6 different types of fabric, according to their use: polyester shirts, linen shirts, T-shirts, polo T-shirts, women’s and girls’ dresses, and the latest generation of textiles for sports. We considered comparison between this latest material and the more traditional
Z UPF ¼
400
290
Z E k ek =
400
Ek ek T k
290
Table 1. Ultraviolet protection factor and protection values for different biological effects of ultraviolet radiation to skin related to cover percentage of the fabric, color and destination. Percentage of UVA transmittance as well as protection rating based in EU standard are also represented. Destination
Color
Linen shirt 100% L
White Beige Blue-sky Green Black White Beige Blue-sky Blue Red White Pink Blue-sky White Blue Red White Yellow Pink Red Blue White Pink Red Blue
Shirt 50% PS-50% C
Woman/Girl Summer dress 45% PS-55% C Polo T-shirt 100% C T-shirt 100% C
Technical sport T-shirt 100% PS
Cover%
UPF
Vit D
NMSC
PHINM
PHAG
5 11 10 14 15 21 14 12 34 31 95 137 105 71 105 114 41 42 49 118 125 53 40 49 70
5 11 9 15 18 23 20 15 41 34 106 148 118 74 121 135 39 45 53 133 141 61 42 53 112
5 11 10 15 20 21 15 13 37 33 108 150 118 74 120 135 41 43 51 137 147 58 41 51 83
5 11 10 16 19 18 13 11 32 31 114 170 124 72 130 135 46 45 50 189 195 61 38 50 67
4 8 8 11 11 17 6 6 21 25 139 216 126 78 107 116 44 39 42 170 170 34 33 40 30
56 70 72 83 85 82 73 73 89 88 98 99 96 96 98 99 88 89 94 99 99 95 91 93 97
0.6 0.8 0.7 1.1 1.0 3.6 2.5 1.2 1.4 1.9 3.6 0.2 1.2 1.3 0.6 0.8 3.4 1.4 1.6 0.8 0.8 2.1 1.3 1.0 0.8
UVA transmittance
Protection rating
Low Low Low Low Low Good Low Low Very Good Very Good Excellent Excellent Excellent Excellent Excellent Excellent Excellent Excellent Excellent Excellent Excellent Excellent Excellent Excellent Excellent
25.4 19.3 20.1 16.6 15.7 6.2 19.4 19.8 5.1 4.0 7.6 5.6 9.2 1.8 0.9 0.9 1.5 3.2 2.0 0.6 0.6 4.1 3.1 3.1 4.0
2.0 6.3 3.7 5.5 3.2 0.6 0.4 0.5 0.4 0.4 0.6 0.4 1.0 0.2 0.1 0.1 0.1 0.2 0.1 0.1 0.2 0.1 0.3 0.3 0.2
Vit D, previtamin D3; NMSC, nonmelanoma skin cancer; PHINM, photoimmunosupression; PHAG, photoaging; L, Linen; PS, polyester; C, cotton.
Photochemistry and Photobiology, 2014, 90
1201
Figure 1. Microscope images of different fabrics analyzed in the study. (A) 100% Linen shirt, (B) 50% cotton- 50% Polyester shirt, (C) 100% cotton T-shirt, (D) 100% cotton polo T-shirt, (E) 100% Polyester bilayer technical sports T-shirt. Images at a magnification of 409 .
SD UPF ¼ UFP ta=2; N1 pffiffiffiffi N UPF = final UPF; UFP = mean UPF of N = 5 samples; ta/2, N1, Student t value with a confidence interval a = 0.05; SD, standard deviation. The UPF was classified into three categories (UPF: 15–24 Good Protection, 15–39 Very Good, 40–50+ Excellent) according to the EU norms. Following the same procedure as for the calculation of the UPF, protection factors of fabrics were also calculated for different ultravioletdependant biological effects in skin, i.e. the action spectra of previtamin D3 (20) production (maximal spectral irradiance 295-300 nm), nonmelanoma skin cancer (21) (295–300 nm), photoimmunosupression (22) (270 nm) and photoaging (23) (340 nm). The final protection values were considered to be the mean protection value given by five samples of each fabric. The protection factor against UVA radiation (UVAPF) in the range of wavelengths between 315 and 400 nm was also analyzed for different fabrics. The UVAPF value is the average transmittance value obtained at each wavelength in this range. The final UVAPF of each sample was obtained from the mean value of five replicates. A minimum threshold of mean UVA transmittance was established according to regulations (less than 5% UVA transmittance).
Cover. To correlate the UPF value with the different physical characteristics of the fabrics, the percentage cover was calculated using image analysis. This technique enables the estimation of the percentage area occupied by the fibers and the respective free space for light transmission in a given area. The technique is based on obtaining a magnified monochrome image of each fabric using an optical microscope (Nikon Eclipse E-400). The microscope observation parameters were adjusted and remained unchanged for all the fabric samples. The adjusted parameters were as follows: 1 Magnification: 409. 2 Diaphragm: Fully open. 3 Light spot: Iris fully open. The microscope was coupled to a digital photocamera (Polaroid DMC1 model) that recorded the image in grayscale. The image of each fabric was treated with an image analysis program (v 6.3 Visilog Noesis, France). The software assigns each image pixel a monochromatic value between 0 and 255, corresponding to a grayscale, where 0 represents the ideal black and 255 the ideal white. The percentage area corresponding to free space in the fabric was calculated with respect to the area occupied by the fibers. Areas with pixel values above 150 were considered to be free spaces. The percentage coverage was determined as 100% free space. The coverage was calculated for each of five replicates of fabric as the arithmetic mean of 10 measurements in different parts of each replicate.
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Aguilera et al. Jose
Statistical analysis For the different fabric samples (n = 5), we calculated the mean and standard deviations, making statistical corrections for the calculation of the final UPF with a confidence interval of 95% given by the Student t. The significance of the differences between mean values was calculated using one-way analysis of variance (ANOVA), followed by a multiple range Tukey b test. Differences were considered significant when the P value was
New Advances in Protection Against Solar Ultraviolet Radiation in Textiles for Summer Clothing Aguilera*, Marıa Victoria de Ga lvez, Cristina Sa nchez-Rolda n and Enrique Herrera-Ceballos Jose Photobiological Dermatology Laboratory, Medical Research Centre, Department of Dermatology and Medicine, Faculty of Medicine, University of Malaga, Malaga, Spain Received 10 March 2014, accepted 14 May 2014, DOI: 10.1111/php.12292
ABSTRACT Clothing is considered one of the most important tools for photoprotection against harmful solar ultraviolet radiation (UVR). The standard for sun-protective clothing is based on erythema despite other biological effects of UVR on the skin. We analyzed the potential protection against UVR in fabrics destined for summer clothing based on several action spectra. We examined 50 garments classified by type of fabric composition, structure of the fiber yarn and color. The ultraviolet protection factor was calculated based on fabric ultraviolet transmittance corrected for erythema according to the EU standard E-13758 as well as the UVA transmittance of fabrics. UVR protection was also analyzed in base of different action spectra as for previtamin D3, nonmelanoma skin cancer, photoimmunosuppression and photoaging. Most knitted fabrics used for sports T-shirts offered excellent ratings for ultraviolet protection while normal shirts showed very low ratings, particularly against photoaging. The cover is the most influential variable in fabric photoprotection, having an exponential relationship with the UPF. The relation between cover and UVA protection was linearly negative. Information about ultraviolet protection in textiles used for summer clothing should be included in labeling as some types of fabrics, especially those used for shirts, offer very low UVR protection.
INTRODUCTION Several epidemiological studies have shown a significant increase in the incidence of diseases resulting from solar ultraviolet action. Reasons for this increase include an increased life expectancy, changes in lifestyle habits resulting in increased sun exposure (and its artificial alternative), the type of clothes worn, and in certain latitudes a decrease in the ozone layer. In Spain, photoprotection is one of the most important social objectives in the prevention of the risks incurred by sun exposure. This is related with the geographical situation of Spain in latitudes with more than 300 days of sunshine per year, and the associated national and international tourism. The incidence data of skin cancer are similar to those of other European Mediterranean countries. During the first decade of this century, the adjusted mean incidence per 100 000 habitants was 82.6 for basal cell *Corresponding author email: [email protected] (Jose Aguilera) © 2014 The American Society of Photobiology
carcinoma, 19.03 for squamous cell carcinoma and 6.7 for malignant melanoma (1). In view of these figures, primary prevention is seen as paramount to tackle the problem of skin cancer from the standpoint of public health. Accordingly, application of the standards on the degree of protection afforded by the various photoprotection methods (sunscreen, hats and sunglasses) is fundamental. These laws are now clearly disseminated and accepted in the community. Considerable interest has recently been given to the degree of solar protection afforded by fabrics. WHO and several photoprotection associations have recommended the protection by fabrics as the first line of defense against solar UV, in addition to the use of photoprotective creams, hats and glasses. This has led textile manufacturers to establish new lines of research and development in fibers, dyes, detergents and finished products to ensure the highest degree of photoprotection (2–5). Thus, as an information about the degree of protection provided by these fabrics needs to be given in a standardized form, different in vitro methods of study have been examined (6,7), methods that correlate perfectly with the in vivo protective measurements (7–9). Recently, the European Commission for Standardization (CEN) has developed and standardized the method for estimating protection offered by solar radiation fabrics in Europe (European standard EN 13758) (10,11). The method, based on in vitro measurements from the transmittance values of the fabric and corrected for the erythemal action spectrum determines the Ultraviolet Protection Factor (UPF) of textiles. A UPF value of 40 or higher has been determined to represent a sufficient level of fabric protection for extreme exposure in any location. This level also takes into account protection in situations of decreased fabric UPF values (e.g. stretching, moisture and washing) (11). Although it is generally considered that clothing provides sufficient protection against solar ultraviolet radiation, in many cases this may not be entirely the case. Even fabrics that a priori appear not to possess light transmittance are able to let significant amounts of ultraviolet radiation through, enough to produce erythema (12,13). In the case of fabrics with light textures, such as those used for summer clothes, the erythema risk is even higher (14). In latitudes like those of central and southern Spain, which have more than 300 days of sunshine per year, the mean erythemal irradiance at midday in summer reaches ultraviolet index values of 8–9 (15,16). Therefore, clothing should incorporate solar protection, at least that designed for summer wear and particularly that made for children, the elderly, professionals exposed to high solar doses and, if possible, photosensitive
1199
1200
Aguilera et al. Jose
patients. Herein lies one of the limitations in the standardization of ultraviolet protection offered by fabrics. Despite the existence of official standards based on erythema for ultraviolet protection of textiles, a series of biological effects take place in the skin after exposure to solar radiation that need to be considered for the complete evaluation of the photoprotection offered by fabrics, with special emphasis on UVA protection and such conditions as photoaging or skin photosensitivity. Yet many fabrics that provide good protection against sunburn may provide inadequate protection against photosensitization by the intrinsic or extrinsic absorbance of molecules or against (pre)malignant lesions. Patients with xeroderma pigmentosum or solar urticaria have been reported to experience typical lesions of the disease in areas covered by light-colored fabrics or areas of low coverage (17,18). The aim, therefore, of this study was to analyze the protection capability against solar ultraviolet radiation of various different fabrics used for summer clothing. We examined a set of biological action spectra depending on both the UVB and UVA region of the solar spectrum. Following EU standards, the UPF (based on erythema) as well as the UVA transmittance were analyzed in relation to textile composition, fiber structure and fabric color.
summer fabrics interesting given its extremely rapid market acceptance. Two main groups of clothing could be differentiated: woven shirts and weft-knit sports T-shirts. We considered the fabric used for technical sports T-shirts as knit fabric after image analysis of the yarn, despite the bilayer composition of this sweat-reducing fabric. Within each different type of fabric, we also analyzed the different colors to determine the degree of dye or pigment staining of the fabric with relation to its ability to filter ultraviolet radiation. The UPF was calculated according to the European standard for solar ultraviolet protective properties of fabrics (EN-13 758) (10). The calculation is based on estimating the solar ultraviolet radiation transmittance of the fabric at different wavelengths between 290 and 400 nm and corrected for its relative effectiveness at delaying erythema in human skin (from the CIE reference action spectrum) (19). Briefly, each fabric sample was placed on the sensor (Ulbrich sphere type) of a Macam SR-2210 double monochromator spectroradiometer (Macam, Scotland) and illuminated with a 300 W Oriel solar simulator (Oriel, Newport Corporation, Irvine, USA). The sample was spread evenly and without tension to avoid optical changes due to alterations in the geometry of the fabric. For each wavelength, the spectral irradiation was multiplied by its relative effectiveness at producing delayed erythema and by the transmittance value of the fabric. The UPF was calculated using the following formula:
MATERIALS AND METHODS
where UPF, ultraviolet protection factor; E, spectral irradiance; e, relative effectiveness for erythema; T, transmittance of the fabric. The UPF value was calculated from the arithmetic mean of the UPF of 5 independent samples of the same fabric. Following EU norms, the final UPF of the sample was obtained after statistical correction. The measurement error was subtracted from the mean UPF. This error was calculated from the standard deviation of the UPF for a confidence interval of 99%, given by the Student-t value. Thus, the UPF has a 99% probability of being the real UPF of the sample. The final UPF was calculated according to the following formula:
A total of 50 fabrics were analyzed, sorted by: textile type, use, composition and color (Table 1). From a practical standpoint, we examined a series of textiles mainly used for traditional clothing worn in summer. Microscopic analysis of the fabrics (Fig. 1) showed that each different type corresponds to a particular structure, yarn and composition. Thus, we were able to determine 6 different types of fabric, according to their use: polyester shirts, linen shirts, T-shirts, polo T-shirts, women’s and girls’ dresses, and the latest generation of textiles for sports. We considered comparison between this latest material and the more traditional
Z UPF ¼
400
290
Z E k ek =
400
Ek ek T k
290
Table 1. Ultraviolet protection factor and protection values for different biological effects of ultraviolet radiation to skin related to cover percentage of the fabric, color and destination. Percentage of UVA transmittance as well as protection rating based in EU standard are also represented. Destination
Color
Linen shirt 100% L
White Beige Blue-sky Green Black White Beige Blue-sky Blue Red White Pink Blue-sky White Blue Red White Yellow Pink Red Blue White Pink Red Blue
Shirt 50% PS-50% C
Woman/Girl Summer dress 45% PS-55% C Polo T-shirt 100% C T-shirt 100% C
Technical sport T-shirt 100% PS
Cover%
UPF
Vit D
NMSC
PHINM
PHAG
5 11 10 14 15 21 14 12 34 31 95 137 105 71 105 114 41 42 49 118 125 53 40 49 70
5 11 9 15 18 23 20 15 41 34 106 148 118 74 121 135 39 45 53 133 141 61 42 53 112
5 11 10 15 20 21 15 13 37 33 108 150 118 74 120 135 41 43 51 137 147 58 41 51 83
5 11 10 16 19 18 13 11 32 31 114 170 124 72 130 135 46 45 50 189 195 61 38 50 67
4 8 8 11 11 17 6 6 21 25 139 216 126 78 107 116 44 39 42 170 170 34 33 40 30
56 70 72 83 85 82 73 73 89 88 98 99 96 96 98 99 88 89 94 99 99 95 91 93 97
0.6 0.8 0.7 1.1 1.0 3.6 2.5 1.2 1.4 1.9 3.6 0.2 1.2 1.3 0.6 0.8 3.4 1.4 1.6 0.8 0.8 2.1 1.3 1.0 0.8
UVA transmittance
Protection rating
Low Low Low Low Low Good Low Low Very Good Very Good Excellent Excellent Excellent Excellent Excellent Excellent Excellent Excellent Excellent Excellent Excellent Excellent Excellent Excellent Excellent
25.4 19.3 20.1 16.6 15.7 6.2 19.4 19.8 5.1 4.0 7.6 5.6 9.2 1.8 0.9 0.9 1.5 3.2 2.0 0.6 0.6 4.1 3.1 3.1 4.0
2.0 6.3 3.7 5.5 3.2 0.6 0.4 0.5 0.4 0.4 0.6 0.4 1.0 0.2 0.1 0.1 0.1 0.2 0.1 0.1 0.2 0.1 0.3 0.3 0.2
Vit D, previtamin D3; NMSC, nonmelanoma skin cancer; PHINM, photoimmunosupression; PHAG, photoaging; L, Linen; PS, polyester; C, cotton.
Photochemistry and Photobiology, 2014, 90
1201
Figure 1. Microscope images of different fabrics analyzed in the study. (A) 100% Linen shirt, (B) 50% cotton- 50% Polyester shirt, (C) 100% cotton T-shirt, (D) 100% cotton polo T-shirt, (E) 100% Polyester bilayer technical sports T-shirt. Images at a magnification of 409 .
SD UPF ¼ UFP ta=2; N1 pffiffiffiffi N UPF = final UPF; UFP = mean UPF of N = 5 samples; ta/2, N1, Student t value with a confidence interval a = 0.05; SD, standard deviation. The UPF was classified into three categories (UPF: 15–24 Good Protection, 15–39 Very Good, 40–50+ Excellent) according to the EU norms. Following the same procedure as for the calculation of the UPF, protection factors of fabrics were also calculated for different ultravioletdependant biological effects in skin, i.e. the action spectra of previtamin D3 (20) production (maximal spectral irradiance 295-300 nm), nonmelanoma skin cancer (21) (295–300 nm), photoimmunosupression (22) (270 nm) and photoaging (23) (340 nm). The final protection values were considered to be the mean protection value given by five samples of each fabric. The protection factor against UVA radiation (UVAPF) in the range of wavelengths between 315 and 400 nm was also analyzed for different fabrics. The UVAPF value is the average transmittance value obtained at each wavelength in this range. The final UVAPF of each sample was obtained from the mean value of five replicates. A minimum threshold of mean UVA transmittance was established according to regulations (less than 5% UVA transmittance).
Cover. To correlate the UPF value with the different physical characteristics of the fabrics, the percentage cover was calculated using image analysis. This technique enables the estimation of the percentage area occupied by the fibers and the respective free space for light transmission in a given area. The technique is based on obtaining a magnified monochrome image of each fabric using an optical microscope (Nikon Eclipse E-400). The microscope observation parameters were adjusted and remained unchanged for all the fabric samples. The adjusted parameters were as follows: 1 Magnification: 409. 2 Diaphragm: Fully open. 3 Light spot: Iris fully open. The microscope was coupled to a digital photocamera (Polaroid DMC1 model) that recorded the image in grayscale. The image of each fabric was treated with an image analysis program (v 6.3 Visilog Noesis, France). The software assigns each image pixel a monochromatic value between 0 and 255, corresponding to a grayscale, where 0 represents the ideal black and 255 the ideal white. The percentage area corresponding to free space in the fabric was calculated with respect to the area occupied by the fibers. Areas with pixel values above 150 were considered to be free spaces. The percentage coverage was determined as 100% free space. The coverage was calculated for each of five replicates of fabric as the arithmetic mean of 10 measurements in different parts of each replicate.
1202
Aguilera et al. Jose
Statistical analysis For the different fabric samples (n = 5), we calculated the mean and standard deviations, making statistical corrections for the calculation of the final UPF with a confidence interval of 95% given by the Student t. The significance of the differences between mean values was calculated using one-way analysis of variance (ANOVA), followed by a multiple range Tukey b test. Differences were considered significant when the P value was
