Chapter 3: Ultraviolet protection of clothing – Functional Textiles for Improved Performance, Protection and Health

3

Ultraviolet protection of clothing

T. Gambichler,     Ruhr University Bochum, Germany

Abstract:

This chapter discusses the main aspects playing a role in the prevention of ultraviolet (UV)-induced skin cancer and photodermatoses by means of clothing. The chapter first reviews the in vitro and in vivo test methods and standards on sun-protective clothing. It then describes various fabric parameters (e.g. composition, construction, dye) and other factors that can have an influence on the UV-blocking properties of clothing. The chapter concludes with a brief outlook on the future of sun-protective garments.

Key words

ultraviolet radiation

skin cancer

photodermatoses

textiles

clothing

3.1 Introduction

Skin cancer is the most common type of cancer in the United States. In 2006, more than one million people were diagnosed as having basal cell carcinoma (BCC) or squamous cell carcinoma (SCC), resulting in approximately 2200 deaths from both cancers combined. Malignant melanoma (MM), the third and most often fatal type of skin cancer, was diagnosed in approximately 59 940 people and accounted for about 8110 deaths in 2007. Between 1975 and 2004, the annual age-adjusted incidence rate for MM (new cases diagnosed per 100 000 people) nearly tripled, from 6.8 to 18.5 cases per 100 000. The rate of deaths attributed to MM also increased by about 60%, from 1.6 to 2.6 per 100 000 people (Cho and Chiang, 2010; Greenlee et al., 2000; Gruber and Armstrong, 2006; Lucas et al., 2008; Tucker, 2009).

Solar ultraviolet (UV) radiation is ubiquitous during daylight hours. Ambient ground-level UV comprises mainly UVA (400–315 nm) plus a small proportion (< 10%, variable by time of day, season and location) of UVB (315–280 nm). Within-person and between-person UV doses vary greatly, depending on location, time of day and season, clothing habits and behavior and skin pigmentation (Holick and Jung, 1999). Exposure to UV radiation on the skin results in clearly demonstrable mutagenic effects. The p53 suppressor gene, which is frequently mutated in skin cancers, is believed to be an early target of the UV-radiation-induced neoplasms (Soehnge et al., 1997). Although there is no direct way that the active wavelengths for the development of skin cancer in human beings can be determined, there is indirect evidence demonstrating probable ranges. In terms of SCC in albino hairless mice, the action spectrum has been determined to have a strong peak at 293 nm with secondary peaks at 354 and 380 nm. The primary wavelength influencing melanoma risk appears to be in the UVB range. However, studies in fish and opossums have also shown a small effect on MM development as a result of exposure to UVA wavelengths (De Gruijl et al., 1993; Ouhtit et al., 1998; Soehnge et al., 1997; Trappey et al., 2010). Fair-skinned individuals who are more sensitive to the effects of exposure at these wavelengths are at higher risk for the development of skin cancer. In addition, skin cancer rates are also increased in persons with increased artificial UV exposure through tanning salons. The amount of average annual UV radiation correlates with the incidence of skin cancer. There is a direct relationship between the incidence of non-melanoma skin cancer and latitude. The closer an individual is to the equator, the greater the UV energy to which they are exposed (Boniol et al., 2005; Setlow et al., 1993). It has been demonstrated that there is a direct correlation between BCC and SCC incidence and latitude. In terms of melanoma, the relationship is not as clear-cut. MM mortality in the United States and Canada has also been shown to directly correlate with ambient UV exposure. The correlation of MM incidence to UV-radiation exposure is greater when ambient UVA radiation is also included. High-altitude regions tend to have a higher melanoma rate that may be related to the higher UV fluences noted at these sites. MM risk has also been noted to be directly related to annual UV exposure (Boniol et al., 2005; Moan et al., 1999; Rigel et al., 1999; Setlow et al., 1993).

Apart from avoidance of the sun – particularly in peak hours – the most frequently used form of UV protection is the application of sunscreens. The use of textiles as a means of sun protection has been underrated in previous education campaigns, even though suitable clothing potentially offers usually simple and effective broadband protection against the sun (Altmeyer et al., 1997; Gies, 2007; Glanz et al., 2008; Hatch and Osterwalder, 2006; Hoffmann et al., 2001a). However, following comments over years by patients, usually from fair-skinned men, that they sunburnt or developed photosensitive disorders through their clothing, it was decided first of all in Australia, to undertake systematic investigations to study UV-protective properties of clothing. In Australia cancer council education campaigns have long urged the use of clothing in conjunction with hats, sunglasses and sunscreens as UV protection (Dobbinson et al., 2008). However, a number of studies have recently shown that, contrary to popular opinion, some textiles provide insufficient UV protection. These studies showed that more than one third of commercial summer clothing gives a UV protection factor (UPF) of less than 15 (Dummer and Osterwalder, 2000; Gambichler et al., 2001b; Gies et al., 1999). Analogous to the sun protection factor (SPF) of sunscreens, the UPF is a multiplying factor which permits calculation of one’s extended time in the sun, when protected by clothes.

Not only skin cancer formation but also photoaging and photosensitive disorders (e.g. polymorphous light eruption, lupus erythematosus, porphyrias, solar urticaria and phototoxic/photoallergic reactions) may be prevented by UV-protective clothing. Consequently, the use of suitable textiles, which block UVB as well as UVA radiation, has been recommended for photosensitive patients (Gambichler et al., 2002b, 2009a; O’Quinn and Wagner, 1998; Roelandts, 2000). Most of the photosensitive diseases are predominantly provoked by wavelengths in the UVA range (Gambichler et al., 2009a) and in some of these disorders (e.g. solar urticaria, chronic actinic dermatitis) even extremely small UV doses can lead to exacerbation. The latter conditions can also be triggered by visible light. Interestingly, the use of optical whiteners in clothing potentially transforms UVA radiation into visible light, so that in particular cases solar urticaria may be even enhanced through clothing (Gardeazabal et al., 1998). Van den Keybus et al. (2006) attempted to determine whether or not the UPF of a particular textile is a good parameter for gauging its protection in the visible light range and concluded that a protection factor of textile materials against visible light needs to be developed. The authors concluded that this development should go beyond the protection factor definition used in this chapter, which has some limitations, and should take into account the exact action spectrum for which the protection is needed.

In addition to the human suffering caused by skin cancer and photosensitive diseases, there is also a significant economic burden due to the costs of preventive efforts, diagnosis, treatment and care of terminally ill patients. Although people are aware of the hazards of sunlight, under-protection because of inadequate application of sunscreen (e.g. amount < 2 mg/cm2; no reapply; skipping ears, neck, etc.) and insufficient textile photoprotection, coupled with overexposure to the sun (prolonging duration of sun exposure by using inadequate UV-protective tools) may partially explain why skin cancer incidences still increase. The data of several studies indicate that some aspects of sun protection are being practiced consistently, while others, such as the use of UV-protective clothing, are not (Barankin et al., 2001; Robinson et al., 2000). As recommended by the American Academy of Dermatology and other organizations, for example, avoiding deliberate tanning with indoor and outdoor light, seeking shade and limiting exposure during peak hours need to be included to sun-protective strategies (Goldsmith et al., 1996; Hall et al., 1997; Holman et al., 1983; Miles et al., 2005).

3.2 In vitro and in vivo testing of the UV protection factor

Direct and diffuse UV transmittance through a fabric is the crucial factor determining the UV protection of textiles. Simple radiometric broadband UV dosimetry is only suitable for measurements where the relative variation in the UPF is required. By contrast, spectroradiometers and spectrophotometers are suitable for the assessment of the spectral irradiance. These devices collect both transmitted and scattered radiation with the aid of an integrating sphere positioned behind the textile sample. Although spectrophotometers fitted with a double monochromator have a large dynamic range and high accuracy, regular scans of the UV source, e.g. deuterium or xenon arc lamps, are required to provide reference data (Capjack et al., 1994; Gies et al., 1994, 1997). As suggested by Australian, American and European standard documents the spectrophotometer should be fitted with a fluorescence filter, e.g. UG-11 (Schott, Mainz, Germany) to minimize errors caused by fluorescence from whitening agents (AATCC, 183–1998, 2000; AS/NZS 4399, 1996; EN 13758–1, 2002).

The spectrophotometric measurements are usually performed in the wavelength range of 290–400 nm in 5 nm steps or less (Laperre and Gambichler, 2003). Spectrophotometric measurements of textiles are generally made under ‘worst-case’ conditions, with collimated radiation beams at right angles to the fabric. For UPF determination, at least four textile samples must be taken from a garment – two in the machine direction and two in the crossmachine direction. To determine the in vitro UPF the spectral irradiance (both source* and transmitted spectrum) is weighted against the erythemal action spectrum (Diffey, 1998), and the UPF is calculated as follows:

where = relative erythemal spectral effectiveness; = solar spectral irradiance in W/m2 (Albuquerque, New Mexico, 37.8° S, 17 January 1990)*; = spectral transmission of the sample; = bandwidth in nm; λ = wavelength in nm; the integrals (∫) are calculated over the wavelength range of 290–400 nm.

As mentioned before, the UPF is defined as the ratio of the average effective UV-radiation irradiance calculated for unprotected skin to the average effective UV-radiation irradiance calculated for skin protected by the test fabric (AS/NZS 4399, 1996). Intra-and interlaboratory comparative trials indicate that spectrophotometry is a precise test method for the determination of the UPF, in particular for samples with UPFs below 50 (Gies et al., 1994; Hoffmann et al., 2001b; Laperre et al., 2001). UPFs greater than 50 are only of theoretical interest as even in Australia the maximum daily UV exposure is less than 40 minimal erythema doses (MEDs). Moreover, Gies et al. (2003) recently presented results from an intercomparison involving ten independent testing laboratories and 11 different UVR transmission measurement instruments. In addition to comparing the measured UPF, this intercomparison also incorporates detailed scan results from all ten laboratories and highlights differences in performance of the various instruments in different wavelength regions. Careful examination of these differences can indicate where changes to the systems could be made to allow improvements both in equipment performance and in agreement of the final results. The variability in the measurements of UPF in the study of Gies et al. (2003) suggests that the protection categories in standards may need to be broadened.

Analogous to SPF testing of sunscreens in vivo measurements in human volunteers with the sun as UV source are extremely impracticable for the determination of the UPF. In general, xenon arc solar simulators with collimated radiation beams are used with filters to absorb wavelength below 290 nm and to reduce visible and infrared radiation. Stanford et al. (1997) and Gies et al. (2000) reported in vivo test protocols which are not based on previous in vitro testing. In most studies, however, the in vivo method has been conducted by in vivo checking of the UPF values measured in vitro (Gambichler et al., 2001a, 2002a, 2002b; Gies et al., 2000; Greenoak and Pailthorpe, 1996; Hoffmann et al., 2000; Lowe et al., 1995; Menzies et al., 1991). Based on the skin phototype the MED is determined with incremental UVB doses on the upper back of a subject and is read after 24 h. To measure the MED of the protected skin the textile is placed on the skin of the other side of the back (Gambichler et al., 2001a).The incremental UVB doses for determination of the MED of unprotected skin are multiplied with UPF determined in vitro resulting in incremental UVB doses for the MED testing of the protected skin. If the in vitro method is in agreement with the in vivo method, the ratio of the MED of protected skin to the MED of unprotected skin results in the original in vitro UPF. Several studies (Gambichler et al., 2001a; Greenoak and Pailthorpe, 1996; Hoffmann et al., 2000; Menzies et al., 1991), however, have shown that the UPFs determined with the in vivo method are significantly lower than the UPF values obtained in vitro when the fabric samples were tested ‘on skin’. By contrast, Césarini et al. (2001) and Gies et al. (2000) observed no difference between UPF values obtained by in vitro and in vivo testing. In two studies, in vivo testing was also performed in the ‘off skin’ modus which corresponds rather to a real wearing condition. It was shown that UPF values obtained by the in vivo ‘off skin’ testing differed insignificantly from UPF values obtained by the in vitro method (Gambichler et al., 2001a; Menzies et al., 1991). The data inconsistency of these studies is certainly due to different methodology (e.g. different test protocols, UV sources and textile materials).

UV dosimetry has been used to measure erythemal UV exposures beneath and above textile materials. Similarly, polysulphone films have been employed in in vivo simulated studies as small portable badges monitoring UV doses on manikins and mobile subjects (Holman et al., 1983; Moehrle and Garbe, 2000; Parisi et al., 2000; Ravishankar and Diffey, 1997). Ravishankar and Diffey (1997) concluded that the protection provided by textiles worn in sunlight is, on average, 50% higher than obtained by conventional in vitro testing using collimated radiation beams. Thin film polymer such as poly-sulphone degrades after exposure to UV radiation, especially in the UVB range. The optical absorbance increases in a dose-dependent manner. The polysulphone and CR-39 films show high sensitivities compared to the MED curve between 312 and 330 nm. However, sensitivity is low at wavelength below 305 nm and above 335 nm. In contrast, the sensitivity curve of biological UV dosimeters such as DLR biofilm (B.subtilis) provides good similarity to the action spectrum for UV-induced erythema in human skin. The DRL biofilm is a wavelength and time integrating biological UV dosimeter which weights the UV radiation according to its DNA-damaging potential (Quintern et al., 1997). Prior to measurement, the UV dosimeters have to be calibrated to the UV source (e.g. sun, solar simulator). The effective UV doses are calculated using the calibration curve. The UPF is then calculated by dividing the UV dose recorded on the textile-unprotected site by the dose received through the textile at the adjacent skin site. It was shown that cycling jerseys have comparable UPF values when tested spectrophotometrically according to the Australian standard or under stationary sun exposure with DRL biofilms (AS/NZS 4399, 1996; Moehrle and Garbe, 2000). In accordance with results reported by Ravishankar and Diffey (1997), however, the jerseys revealed a much higher UPF when tested under ‘real’ conditions during cycling. We also conducted a field-based study with biofilms and found that the UPF of a garment worn during outdoor activities is significantly higher than the UPF measured in the laboratory (Gambichler et al., 2002c). Furthermore, we observed in the laboratory-based study that biological dosimetry performed with solar-simulated radiation revealed significantly lower UPFs than spectrphotometric measurements (Gambichler et al., 2002c).

3.3 Standards for sun-protective clothing

The first standard for sun-protective clothing was published jointly by Standards Australia and Standards New Zealand in 1996. This standard, referred to as AS/NZS 4399 has set requirements for determining and labeling the UPF of sun-protective fabrics and other items that are worn in close proximity to the skin (AS/NZS 4399, 1996). Based on the standard, spectrophotometrically assessed UPF is for a fabric material and does not address the degree of protection that is afforded by the design of a garment. The effects of stretch, wetness, wear and use are not included in the AS/NZS 4399. According to the Australian standard, UPFs are classified in three categories: UPFs of 15–24 (ratings 15 and 20) offer good protection; UPFs of 25–39 (ratings 25, 30 and 35), very good protection; and UPFs of 40 and higher (ratings 40, 45, 50 and 50 +), excellent protection. Fabrics with a UPF of less than 15 are not labeled. About ten years ago, three standard documents that pertain to the testing and labeling of UV-protective textile products were published by the American Society for Testing and Materials (ASTM) and the American Association of Textile Chemists and Colorists (AATCC). The titles of these documents, which are available for purchase at www.astm.org and www.aatcc.org are: ASTM D 6544 ‘Standard Practice for the Preparation of Textiles Prior to UV Transmission Testing’, AATCC 183 ‘Test Method for Transmittance or Blocking of Erythemally Weighted Ultraviolet Radiation Through Fabrics’, and ASTM 6603 ‘Standard Guide to Labeling of UV-protective Textiles’ (AATCC 183–1998, 2000; ASTM D 6544, 2000; ASTM 6603, 2003). More recently, the European Committee for Standardization (CEN) has developed a standard on requirements for test methods and labeling of sun-protective garments. The first part of the standard (EN 13758–1) deals with all details of test methods (e.g. spectrophotometry measurements) for textile materials and part 2 (EN 13758–2) covers the classification and marking of apparel textiles. UV-protective clothing for which compliance with the European standard is claimed must fulfill all stringent instructions of testing, classification and marking including a UPF larger than 40 (UPF 40 +), average UVA transmission lower than 5%, and design requirements as specified in part 2 of the standard. A pictogram, which is marked with the number of the standard EN 13758–2 and the UPF of 40 +, shall be attached to the garment if it is in compliance with the standard (Gambichler et al., 2006). Moreover, British, Canadian, South African and multinational groups, including the Commission on Illumination (CIE) and also the International Organization for Standardization (ISO) have been engaged in writing UV-protective fabric standard documents.

3.4 Type and construction of fabric

For un-dyed fabrics there are differences in the UV absorbing properties of the fiber. Summer clothing is usually made of cotton, viscose, rayon, linen and polyester or combinations thereof. Other types of materials such as nylon or elastane are also found in steps applications such as bathing suits and nylon stockings. In general, consumers consider lightweight non-synthetic fabrics, e.g. cotton, viscose and linen, the most comfortable for summer textiles (Gambichler et al., 2009b). Comparison of the different types of material in relation to the UPF is difficult and only possible in a limited number of cases. In the case of synthetic fibers (e.g. polyester, polyamide) the analysis is even more difficult because the UV protection of these materials will depend on the type and amount of additives, such as antioxidants or UV stabilizers, to the fiber. In particular, polyester has usually good UV-blocking properties, since this fabric provides relative low UVB transmission probably due to a large conjugated system in the polymer chains (Crews et al., 1999; Davis et al., 1997). Polyester or polyester blends may be the most suitable fabric type for UV-protective garments. However, its permeability for wavelength in the UVA range is frequently higher in comparison to other fiber types (Gambichler et al., 2002b); this could be of significance for many wearers suffering from photosensitive disorders. Bleached cotton and viscose rayon provide relatively low UV protection and are thus transparent to UV radiation. This was recently confirmed by a study of Crews et al. (1999) who reported that bleached cotton print cloth had a UV transmission of 23.7%, whereas unbleached cotton print cloth had a UV transmission of only 14.4%. The influence of bleaching was also evident among the silk fabrics in their study. In comparison to bleached textiles unbleached fabrics such as cotton and silk have better UV-protective properties due to UV absorbing natural pigments and other impurities. Very few studies have taken the ‘fiber-fabric construction-processing’ history of fabrics into consideration to fully elucidate the UV protection abilities of fabrics. Sarkar (2007) recently reported the effect of fabric processing treatments, both chemical and biochemical, on the transmission of UV radiation through selected white and un-dyed fabrics. Sarkar (2007) observed that physical characteristics of fabrics such as thickness, weight and cloth cover were shown to be only partly useful in explaining the UV-protective abilities of fabrics in that the data show anomalies when only physical features of fabrics are considered without considering processing history. However, by taking into account the processing history of fabrics, the UPF values obtained can be fully explained. Sarkar (2007) concluded that chemical processing methods such as desizing and bleaching have a deleterious effect on UV transmission through fabrics. Biochemical processing such as the use of enzymes is comparatively benign and does not adversely impact the UV-protective ability of cotton fabric. Grifoni et al. (2009) recently studied the UV protection properties of two fabrics made of natural fibers (flax and hemp) dyed with some of the most common natural dyes. UV transmittance of fabrics was measured by two methods: one based on the utilization of a spectrophotometer equipped with an integrating sphere (in vitro test), and the other based on outdoor measurements taken by a spectroradiometer. Transmittance measurements were used to calculate the UPF. Experimental results revealed that natural dyes could confer good UV protection, depending mainly on their different UV absorbing properties, provided that the fabric construction already guaranteed good cover. An increase in cover factor caused by the dyeing process was also detected. Weld-dyed fabrics gave the highest protection level. The authors also confirmed that comparison the UPFs calculated by in vitro measurements were generally lower than those based on outdoor data, indicating an underestimation of the actual protection level of tested fabrics assessed by the in vitro test (Grifoni et al., 2009). Sarkar (2004) investigated the UV protection properties of natural fabrics dyed with natural colorants. Three cotton fabrics were dyed with three natural colorants. Fabrics were characterized with respect to fabric construction, weight, thickness and thread count. Sarkar (2004) observed a positive correlation between the weight of the fabric and their UPF values. Similarly, thicker fabrics offered more protection from UV rays. Thread count appears to negatively correlate with UPF. Dyeing with natural colorants dramatically increased the protective abilities of all three fabric constructions. Additionally, within the same fabric type UPF values increased with higher depths of shade. Sarkar (2004) concluded that dyeing cotton fabrics with natural colorants increases the UV-protective abilities of the fabrics and can be considered as an effective protection against UV rays. The UPF of natural fabrics is further enhanced with colorant of dark hues and with high concentration of the colorant in the fabric (Sarkar, 2004).

The fabric construction is a primary determinant of fabric porosity followed by fabric weight and thickness of the textile (Crews et al., 1999). The denser the weave or knitting (smaller yarn-to-yarn spaces), the less the fabric’s porosity – consequently, less UV radiation is transmitted. Spaces between the yarns are frequently larger in a knit than in a woven textile. Further, plain woven textiles have a lower porosity than textiles woven using other weaves (Capjack et al., 1994). For an ‘ideal’ fabric (fibers opaque to UV light) of a particular fiber content and fabric construction, an increase in weight per unit area decreases the fabric porosity – the spaces between the yarns will be smaller in a heavier textile; therefore, less UV radiation is transmitted. However, yarns are usually not opaque to UV radiation and the UPFs of ‘real’ fabrics are therefore lower than the ideal fabric. In most of the studies thickness measurements for the fabrics were not undertaken or reported. However, thickness is a useful parameter for understanding differences in UV protection between fabrics. Crews et al. (1999) reported that thicker, denser fabrics transmit less UV radiation and they concluded that thickness is most useful in explaining differences in UV transmission when differences in percentage cover are also accounted for (Pailthorpe, 1994).

3.5 Fabric color, dyes and UV absorbers

The fabric color may influence the UPF since some dyes have an absorption spectrum extending into the UV spectrum. Enhanced UV protection of dyed textiles depends on the position and intensity of the absorption bands of the dyes in the UV wavelength and the concentration of the dye in the textile. The absorbance of UV radiation can influence many substrate attributes, e.g. fluorescence, photodegradation and UV protection. Generally, dark colors provide better UV protection due to increased UV absorption. This only holds true for the same UV absorbent dye and provided that other characteristics of the textile, e.g. fabric type and construction, are the same. However, dyes within particular hue types can vary considerably in the degree of UV protectiveness due to their individual transmission/absorption characteristics (Srinivasan and Gatewood, 2000). In order to improve UV protection, UV absorbers have recently been added with different techniques. UV absorbers are colorless compounds that absorb in the wavelength range from 280 to 400 nm. Hilfiker et al. (1996) found the cover factor to be useful in predicting the maximum UPF that could be achieved by treating the yarns with UV absorbers. Thus, fabrics could be made opaque to UV radiation with a sufficient level of UV absorber impregnation, and the corresponding UPFs approached the theoretically predicted levels based on the cover factor. Osterwalder and Rohwer (2002) demonstrated that a UV absorber can be brought into contact with a fabric during the wash or rinse cycle of a laundry operation. The high UV transmittance of 30% of a thin, bleached cotton swatch in the dry state (UPF 3) can be reduced tenfold to about 3% (UPF > 30) in ten washes cycles. This is more than the effect achieved by dyestuffs. The authors suggested that the detergent should contain about 0.1–0.3% of the special UV absorber (Osterwalder and Rohwer, 2002; Osterwalder et al., 2000). The same effect can be achieved as early as after one wash cycle with a higher concentration provided by a special laundry additive. Yet another form of application is via rinse cycle fabric conditioner.

Titan dioxide is frequently used as a UV-blocking substance in fabrics. However, the absorptive and scattering properties of titan dioxide particles in the UVA wavelength range are different and depend mainly on the particle size and geometry. Other manufactured UV absorbers also provide less protection from UVA radiation, which should be considered when counseling patients with photosensitive disorders. Nevertheless, UV absorbers are suitable for significantly increasing UPF, especially that of non-dyed lightweight summer fabrics, such as cotton and viscose fabrics (Eckhardt and Rohwer, 2000; Hilfiker et al., 1996; Hoffmann 1998; Hoffmann et al., 1998). Recently, Wang et al. (2005) presented a facile process to prepare uniform dumbbell-shaped ZnO crystallites. They discovered a unique morphological effect on the UV-blocking property. The as-prepared ZnO crystallites were characterized by different criteria including UV-blocking and Raman scattering spectra. The as-prepared structural material demonstrated a significant advance in protective functional treatment and provided a potential commercialization. Furthermore, Behler et al. (2009) showed that the use of electrospun nanofibers with a high load of nanodiamond can provide UV protection and scratch resistance to a variety of surfaces, especially in applications where a combination of mechanical, thermal and dielectric properties is required.

3.6 Effects of environment and fabric use on UV protection factor

Woven textiles do not stretch significantly; however, knitted textiles are prone to stretch causing an increase of fabric porosity with a consequent decrease in UPF. Moon and Pailthorpe (1995) showed that stretching elastane-based garments about 10%, in both the machine and the crossmachine directions, causes a dramatic decrease in the measured UPF of a textile. Their consumer survey also showed that, on average, about 15% stretch is achieved when these textiles are worn. However, the 15% is for power-stretch, which is only a small segment of the clothing market, and elastane-based textiles for ‘tight-fitting’ should not be considered as defined UV-protective clothing. Kimlin et al. (1999) reported that the UPF of 50 denier stockings decreased 868% when stretched 30% from their original size. Notably, the most popular type of stockings (15 denier) provides a UPF less than 2 (Sinclair and Diffey, 1997). The maximum stretch point on the body for tight-fitting garments is the upper back, where textiles can be stretched up to 15%. However, realistically, the effect of stretch on the UPF of a textile may be of significance only for garments with a non-stretched UPF of less than 30, particularly leggings, women’s stockings and swimsuits.

When textiles become wet, by air hydration, perspiration or water, UV transmission through the fabric can significantly change (Khazova et al., 2007). A marked reduction of the UPF was observed for textiles made from cotton and cotton blends. In a field-based study it was recently shown that significant UV exposures may occur beneath the garments, particularly for white cotton fabrics in the wet state. Similar results were also observed in in vivo measurements of cotton and polyester blends (Gambichler et al., 2002a; Jevtic, 1990, Moon and Pailthorpe, 1995). One explanation for this is that the presence of water in the interstices of a fabric reduces optical scattering effects and, hence, increases the UV transmission of the textile. The analogy in the visible spectral range is that T-shirts become see-through when wet. In case of fabrics made of viscose or silk, or in fabrics that have been treated with broadband UV absorbers, the UPF frequently increases when the textile becomes wet. This was also observed in a recent study of modal fabrics treated with titan dioxide (Gambichler et al., 2002a; Hoffmann et al., 1998). Thus, UV protection of wet garments is not necessarily poor.

Most of the fabrics will undergo a combination of relaxation shrinkage and consolidation shrinkage when washed (Kaskel et al., 2001). Thus the spaces between the yarns will decrease and UV protection increases. The effect of laundering on the UPF puts into perspective other fabric parameters and factors which decrease the UPF. Stanford et al. (1995a) conducted laundering trials using cotton T-shirts. They showed that UPFs increased after the first washing and did not change significantly with subsequent washing. For example, the original UPF rating of a new cotton T-shirt was 15, increasing to UPF 35 after the first laundering. These UPFs were also obtained when participants were instructed to wear their T-shirt for 4–8 h per week and to wash their T-shirt once per week for ten wash-and-wear cycles (Stanford et al. 1995b). Wang et al. (2001) observed only a moderate increase of the UPF of cotton fabrics after laundering. They found that adding UV absorbing agents during laundering substantially enhances UPF (Osterwalder et al., 2000; Wang et al., 2001). Recently, Zhou and Crews (1998) reported that UPF of cotton cotton/polyester blend fabrics can be significantly enhanced by repeated laundering of the garment in a detergent containing optical brightening agent. This was not true for fabrics comprised entirely of polyester or nylon. Prolonged wear and tear beyond the ‘standard’ lifetime of a garment may eventually cause thinning of the individual fibers and so alter the UPF. Photostability of a textile and its UV protectiveness is an important requirement for sun-protective clothing (Khazova et al., 2007). Unfortunately, there are only limited data on the stability of the UV protectiveness of a textile against UV radiation or infrared. Below particular wavelengths, photolytic processes of fibers have been observed in various fabrics (linen < 360 nm; cotton < 350 nm; viscose < 340 nm; silk and polyester < 310 nm), independent of other factors, such as temperature, oxygen and hydration. Photo oxidation of fibers can occur above these wavelengths in association with oxidative and hydrolytic processes. For most of the fabrics, durability against thermic effects decreases above 80 °C (Bobeth, 1993).

3.7 Conclusions and outlook

Defined UV-blocking fabrics are not only an important element in the campaign against skin cancer, but also in prevention of photosensitive disorders and photoaging. A lot of work has been done around the world on the test methods of the UPF and factors that affect the UV protection provided by clothing. Because parameters are rarely independent, systematic research to quantify the effect of various manufacturing methods is difficult. The UPF of a garment depends on a number of parameters, including fabric construction, type, color, weight, thickness, finishing processes and presence of additives such as UV absorbing substances (e.g. titan dioxide, brightening agents). Moreover, UV protection of a garment during use depends on wash and wear, including stretch and hydration. Hence, the UPF of a textile is influenced by fabric properties and so complex is the interactive influence of these properties that it is neither possible to predict the UPF or to make generalizations concerning, for example, cotton vs. polyester, nor is it sufficient to hold a fabric to the light and assess the amount of light seen through the spaces. Apparel textiles assigned for UV-protective clothing will therefore be measured and labeled in accordance with a standard document (AATCC 183–1998, 2000; AS/NZS 4399, 1996; EN 13758–1, 2002). Principally, sun-protective clothing needs to be designed with special types of complex weaves allowing the passage of air to promote wearer comfort but to block the passage of sunlight through the textile. Fabrics may include UV absorbers of various types to increase UV protection. It will of course be essential to select substances that have a low potential for irritation and sensitization. Moreover, stringent requirements for the design should be complied with in garments assigned for sun-protective clothing (EN 13758–2, 2003).

A recent German study indicate that more counseling on UV-protective clothing is needed for young, male and lower educated individuals (Eichhorn et al., 2008; Gambichler et al., 2009b). The textile industry should be aware of the increasing demand for labeled sun-protective clothing in particular clothing segments such as baby wear, children wear and leisure wear. Lightweight, breathable, natural fabrics made of cotton and linen are the most frequently preferred textiles. The textile industry may consider these fabrics for the production of labeled sun-protective clothing. However, the UV-blocking capacities of cotton and linen have significantly to be improved (e.g. addition of UV absorbers) before these fabrics can be used for proper sun protection. For all sun-aware consumers, who request definitive UV-protective summer clothing that provides sufficient sun protection both under extreme wearing conditions and in all geographical areas, labeling of a garment in compliance with a standardized test and labeling method is a simple aid in selecting the ‘right’ garment. Indeed, clothing does not suffer from the uncertainties of sunscreen application, including thickness and frequency of application and potential skin sensitization and irritation. Nevertheless, people’s compliance in buying and wearing sun-protective clothing may be impaired by several factors such as price, lack of knowledge and desire to tan.

In conclusion, garments assigned for UV-protective clothing play a significant role in the prevention of skin cancer, photodermatoses and premature skin aging. Further education efforts are necessary to change people’s sun behavior and raise awareness for the use of adequate sun-protective clothing. Clearly, whether there will be a market for labeled UV-protective clothing strongly depends on acceptance and demand from the consumer.

3.8 References

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