Background Apart from sunscreen lotions, clothing provides protection from acute and chronic sun damage. Therefore, it is very important to know the ultraviolet (UV) protection factor (UPF) of textiles, in particular of lightweight summer clothing. Usually, the UPF of a textile is determined by spectrophotometric assessment of the UV transmission (in vitro method).
Objectives To compare the relationship between in vitro tests and in vivo tests of UPF using solar simulators for determination of the minimal erythema dose (MED), applied to 30 different summer textiles.
Methods Thirty summer textiles were spectrophotometrically assessed, and UPFs were calculated with respect to the International Commission on Illumination (CIE) erythemal action spectrum.1 Based on the in vitro UPFs ‘on skin’ and ‘off skin’, in vivo testing was performed using a solar simulator for the determination of the MEDunprotected and MEDprotected.
Results The UPFs obtained from in vivo‘on skin’ testing were significantly (r = 0·95; P < 0·001) lower than the predicted in vitro UPFs. This disparity was also confirmed by chromometric assessment of the MED testing; the erythemal responses measured after textile protection were significantly (P < 0·001) higher than those obtained without protection. However, the in vivo‘off skin’ UPFs did not significantly (r = 0·98; P > 0·05) differ from the in vitro UPFs; comparison of the chromometrically assessed erythemal responses was also insignificant (P > 0·05).
Conclusions The different correlation between in vitro and in vivo measurements of the UPF may be due to the optical–geometrical properties of textiles and the different amount of direct and diffuse radiation passing through the spaces between the yarns. As spectrophotometric measurements of a textile may generally yield lower UPFs than those obtained under average field conditions, the in vitro test method provides ‘safe’ UPF values representing a ‘worst-case scenario’. In contrast to in vitro testing, in vivo methods are much more expensive and time-consuming. Thus, with respect to practicality, spectrophotometric measurements seem to be most suitable for the evaluation of UV protection of textiles.