Influence of wetness on the ultraviolet protection factor (UPF) of textiles: in vitro and in vivo measurements.

Abstract

Clothing is an important product for sunburn protection and skin cancer prevention. The moisture content of a fabric, which can increase during its wearing, may decrease the fabric's capability of protecting the skin from solar UV radiation, that is, lower its UPF (ultraviolet protection factor). Due to limited data about the effect of fabric wetness on UPF, this study was undertaken to investigate the following: (a) the effect of saturating a variety of fabrics with tap water and with salt water on fabric UPF and (b) whether wetted-fabric UPF values reflect only the fact that the fabric is wet during testing or the fact that the skin is hydrated and the fabric is wet. For objective a, 69 summer fabrics were spectrophotometrically (in vitro) assessed when "dry" and when saturated with tap and salt water. In vitro UPFs, percent UVA transmission and percent UVB transmission values were calculated from the transmission data. For objective b, 100% cotton and 100% polyester fabrics were tested in vivo to determine in vivo UPF values. The minimal erythema dose (MED) was determined for each of the 12 subjects on unprotected "dry" skin and on "hydrated" unprotected skin. MEDprotected was determined when the subject's skin was covered with "dry" and with saturated fabric. In vivo UPFs were calculated using this data. Student's paired t-tests were used to determine the effect of wetting. With one exception, in vitro UPF values were the same when the fabrics were saturated with tap water and when they were saturated with salt water. However, saturating the fabrics with water had different effects on the UPF, UVA transmission, and UVB transmission values. For linen, viscose and polyester fabrics, UPF significantly increased. For the cotton fabrics and the polyester + TiO2 fabrics, UPF significantly decreased. For the modal + TiO2 fabrics and the polyester crepe + TiO2 fabrics, UPF significantly increased. From the in vivo testing, the MED of the "hydrated unprotected" skin was not different than the MED of "dry unprotected skin." Values obtained from subtracting dry-fabric in vivo UPF values from dry-fabric in vitro values and subtracting wet-fabric in vivo UPF values from wet-fabric in vitro values are not different. Fabrics do not need to be tested when saturated with tap and with salt water. Testing fabrics wet and dry should be done, as the effect of saturating fabric on UPF value varies. Fortunately, UPF values for wetted fabrics reveal only the effect of increased moisture content in the fabric and have nothing to do with wetting of the skin by the fabric.