Sun protection offered by fabrics: on the relation between effective doses based on different action spectra

Ultraviolet (UV) radiation threshold levels have been suggested by the International Commission on Non Ionising Radiation Protection (ICNIRP). The ICNIRP action spectrum differs from the action spectrum proposed by the International Commission on Illumination (CIE). Industrial hygienist employs the first approach while dermatologists and photobiologists commonly use the CIE spectrum.

By means of the ICNIRP and CIE action spectra we aimed to calculate the ultraviolet protection factor (UPF) for clothing as a function of the UV index, and to elucidate the relation between the two action spectra.

Using a theoretically calculated solar spectrum that was determined by means of radiation transfer modelling the relation between the effective doses were assessed which were obtained by using the ICNIRP or the CIE action spectra. Employing the guidelines set out by the ICNIRP and the CIE the protection requirements for clothing were also calculated.

It was found that the UPF of a textile material should be at least 2.25 times the maximum UV index observed on a cloudless day to comply with the guidelines of the CIE, or should be at least 4.13 times the maximum UV index to comply with the guidelines of the ICNIRP.

In Northern Europe a UPF 40 + should indeed comply with the exposure limits (EL) proposed by the CIE or ICNIRP. However, in Southern Europe, where UV index can, as in Australia, be as high as 11 the EL can in principle be exceeded for outdoor workers or individuals staying outside the whole day. Taken into consideration the exposure geometry a clearly lower UPF seem to be sufficient in a realistic exposure situation. Nevertheless we recommend a UPF 40 + that is sufficient in extreme exposure situations in every geographical location and also resistant against UPF-decreasing effects ('worst case scenario').