UVA and UVB Transmission of Fabrics: Critical Wavelength Based on Absorbance and Effective Dose

<i>Background:</i> The degree to which a fabric protects the skin from ultraviolet (UV) rays is given as its UV protection factor (UPF) that is predominantly influenced by UVB transmission through the fabric. However, the UVA-blocking properties of a fabric are of significance as UVA plays also a role in photocarcinogenesis, photo-aging and provocation of photosensitive disorders. <i>Objectives:</i> The objective of this study was to present some overall performance of the protection against UVA radiation compared to the protection against UVB radiation of apparel fabrics. For this purpose, we aimed to study the ratio of the average UVA and UVB transmission and to calculate the critical wavelength (CW) of a large collection of fabric materials. <i>Methods:</i> We studied 196 different fabric materials. The fabrics were spectrophotometrically assessed in accordance with the European standard (part 1). We determined the mean UVB (290–320 nm) and UVA (320–400 nm) transmission, mean UVB/UVA ratios, maximum UVA transmission and CW based on absorbance and effective dose (ED). <i>Results:</i> We observed that about 90% of the fabrics had UVB/UVA ratios smaller than 1. This indicates that the average UVA transmission was higher than the average UVB transmission. For 20% of the fabrics, the average UVA transmission was at least twice as high as the average UVB transmission. When calculating the CW based on the absorbance for the sample set, we found that the CW of fabric materials is generally higher than 370 nm and is usually close to 380 nm. When the ED was used, a much smaller CW was found compared to the calculations based on absorbance. <i>Conclusions:</i> UVA transmission through fabrics is usually higher than UVB transmission. Despite a high UPF, increased UVA transmission through clothing may be of significance in triggering photosensitive disorders. The UVB/UVA ratio of fabric materials strongly correlates with the CW based on ED. Because frequently a UG-11 fluorescence filter has to be used in UPF assessment, the CW based on the ED is more relevant and less prone to measurement error.