Introduction

The objective of this study was to compare the in vitro and in vivo determination of the ultraviolet protection factor (UPF) of fabrics.
The concept of protection factors makes it possible to compare the protective properties of different materials.
Many fabrics possess a low UV transmission and require no additional treatment.
In order to develop lightweight, functional clothing which ensures a high degree of wearing comfort, however, a number of possibilities for improving UV protection have been developed.

Materials and Methods

Viscose materials

In this study five different viscose fabrics were investigated. Two of these fabrics had undergone a special treatment to confer UV protection (ENKA Sun Viskose). In the case of viscose fibres, UV protection can be optimized through delustering, i.e. the type and concentration of pigments used, e.g. TiO2 (Figure 1).

Figure 1

The improved UV protection is achieved through reflection and / or absorption of the UV rays. Pigments effect a permanent improvement of the protection as they are enveloped by the fibres and thus cannot be washed out.

Testing methods

During the in vitro testing, the UV transmission of the fabric samples was measured in the 280-390 nm wavelength range with a Cary 3 Bio (VARIAN) spectrophotometer. The UPF of the fabrics was then calculated from data obtained.

The in vivo measurements were made on the backs of 10 subjects with healthy skin (Figure 2).

Figure 2

It was used the "on-skin"-method: The sample was put directly on the skin.
A sun simulator served as the radiation source.
The sun protection factor is computed based on the quotient of the necessary minimal erythema dose (MED) of the covered to the uncovered skin.

Results

Figure 3 presents the transmission spectra of the five different viscose materials.

Figure 3

The calculated ultraviolet protection factors shows, that the three fabrics which had received no special treatment yielded UPFs of 2.5, 14 to 16, whereas UPFs between 33 and 35 were measured in the specially treated fabrics (Figure 4).

Figure 4

During the in vivo measurements series, it was noted that the fabrics with low UPFs did not produce the UPF values obtained during the preceding in vitro measurements (Figure 5).

Figure 5

In the specially treated viscose fabrics, on the other hand, the UPF values measured in vivo were at least as high as, and sometimes higher than, the in vitro values (Figure 5).

Discussion

A rising incidence of skin cancer has been observed for years now. Increased exposure to UV radiation is seen as a major factor in the occurrence of neoplasia in the skin. Suitable protective measures are therefore becoming increasingly important.
Textile can provide simple and effective protection against UV radiation.

How successful sun protective clothing is in the prevention of skin cancer will depend primarily on the extent to which the public can be made aware of the need to wear such clothing.
The clothing will be well received by the public, if the following requirements are met:
- lightweight material,
- attractive design,
- wide and airy cut,
- functional clothing and
- high degree of wearing comfort.
Therefore we examined the lightweight viscose material.

A further important point is the testing method which is used. The results has to guarantee the UV protection.

This study has shown that - for fabrics with low UPF values at least - in vitro determination of UPF values is not sufficient.