CONTENTS

Introduction
Human Skin Cancer
Sunscreen and Fabric
The Mouse Model of Cancer
Studies Using Skin Tissue
Drugs and Sunlight
Plant and Algae Growth
Conclusion
Glossary
Bibliography

Predicting Fabric Protection Factors

The testing of people is a time consuming and expensive business. The study hopes to establish a means to be able to assess a fabric without human testing. The second part of the project is looking at ways of predicting the FPF from the geometric properties of the fabric and the measured transmission of the fabric. The transmission of the fabric is how much light goes through it, particularly how much UV radiation. Measurements of FPFs using human subjects is compared to predicted FPFs calculated from UV transmission measurements.

The amount of UV transmission which takes place through a fabric is measured with a spectrophotometer. When light goes through a fabric it scatters and this causes problems, that is the light comes into the fabric and then when it comes out it fans out. This is because fabrics have got holes in them with things sticking out and across fibres. This causes the light to scatter, especially with UV light.

Most spectrometers are set up to look at what just comes straight through. The problem has been that the light that is fanned out in a diffuse transmission is also significant in terms of UV exposure so that straight through penetration measurement is not good enough. “You have to make sure that you get all the light that goes through the fabric.”

The other thing is that the dyes, and the fabric fibre material itself can fluoresce, that is, give off additional light to what is being transmitted. (For example when you go to a disco with black light and people are wearing a white garment with an optical brightener it glows.) This means the researchers have to be careful to exclude this fluorescence. The fluorescence effect fools the spectrometer. The detector thinks that it is actually getting more light through than it really is. Fluorescent light that is emitted in this way is generally not a worry as far as skin cancer is concerned. So the team had to go to enormous lengths to block it out.

This seems to be the only work going on in Australia in which human testing and physical assessment are set side by side and compared. Other groups have tested the transmission properties of various fabrics and there has been media coverage and conference papers coming out of that work. For example, the Courier Mail reported that cotton and polycotton T-shirts don't completely protect you from the sun.

But researchers who were studying UV transmission of fabrics established the results without testing the predicted protectiveness of fabrics on humans. The Fabric Protection Team have found that the relationship between predicted and actual protectiveness is not a simple one. Fabrics are very complicated. Samples of the same material, for example cotton, can have variations in thickness, size of holes, openness of weave. Light transmitted can be scattered in the fibres themselves. Even a single sample can have variations depending on whether it is stretched or sheared.

The first set of measurements they took showed that the predicted FPF based on the transmission of the fabric was different from the measured FPF done with people. Some things seemed to correlate well and some things didn't. They tried to guess why there was the difference. In order to standardise their experiments they worked with uniform metal meshes of different sizes in place of fabrics. This allowed them to change the size of the fibre and change the hole size in a controlled and uniform way and to sort out some problems with the spectrophotometer (such as scattering and fluorescence).

They got a very good correlation between transmission of metal meshes with human testing and this gave them confidence that transmission rates did correlate very well with protectiveness. However when they went back to studying fabrics, the actual fabrics gave a different relationship between measured transmission and the human testing - it was much more elusive. Walker says they felt annoyed about this. But although it was frustrating it threw up opportunities.

The use of the metal meshes allowed them to account for the skin response and some geometric factors such as the size of the holes and the distance between holes so that when these were compared with the fabrics it allowed them to narrow down what factors might be causing the differences with the fabrics. The pattern of how the light gets through the fabric might affect the human response but whether that is the case has not been resolved as yet.

“It appears that people who have been involved in this sort of study have either measured transmissions and assumed that relates to FPF or measured FPF on people and made assumptions about how that relates to transmissions. There really hasn't been a comparison of the two measurements. Our experience has shown that these assumptions may have been wrong.” Walker states “I think that the main upshot of what we have got to say is that it is fairly well established that some of the stuff that has been done, unless it has been done under very controlled circumstances is probably invalid.”

“This is not a big field of study,” says Menzies, “and there wouldn't be more than ten publications so obviously people tend not to investigate as tightly as they can and there is no cross check. People have made an assumption which has gone untested and then we tested it out.” The team has been looking for reasons why transmission doesn't correlate with protectiveness in a group of fabrics that they've been looking at. “We're not prepared to talk about the possible reasons because we are the only group that know that transmission doesn't equal protectiveness. It is dangerous to prepublish a result before its published in a scientific journal. You never know, we might be completely wrong.”

One possible explanation is “very boring” according to the team. That is that when they test a small area of fabric it doesn’t have a uniform pattern (like the metal meshes they have experimented with) but rather its weave is scrunched up in one place and pulled open in another. This would lead to funny results. If variations occur because of the patterns of the weave then averaging weaves is probably reasonable since fabrics move on the skin. It depends how much variability there is, of course. “If you had great big holes in the weave of the textile and other areas are tightly woven you would probably compensate. You would probably take multiple transmissions. The poorest one could be taken as the protectiveness.”

Menzies says, “If we found out that it had something to do with the weave being compact in some places, that would be so tedious-we would have basically wasted two years. But if there are other possibilities, such as differences in the ways the fabrics are configured, then that is much more exciting. There would be need for a lot of further research.”