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

Sunscreen Labelling Issues

One of the controversies surrounding sunscreen labelling at the moment is that sunscreen manufacturers are not able to put sun protection factors above 15 on the sunscreen packages. So 15+ can mean anything from 16-60. There is no way the consumer can know which. Greenoak believes that consumers should be able to know the exact number because a sunscreen with a SPF of 60 will filter out much more ultraviolet light than one with an SPF of 16. “If you are highly sensitive then you want the best protection from the moment you apply the sunscreen.”

Opponents of such labelling point out that the difference in absorption of ultraviolet light between an SPF 15 and an SPF 30 sunscreen is very small, but it is the transmission which matters, and this for a 30 is precisely half the amount of a 15. Greenoak points out that in terms of biological damage, it will take twice as long for that damage to occur if you are wearing a SPF 30 sunscreen than if you are wearing an SPF 15 sunscreen, “so the percentages are kind of meaningless unless you are referring to the biological damage.” Whereas a person who gets burnt in 10 minutes can spend 100 minutes in the sun with an SPF 10 sunscreen before being sunburnt, with an SPF 50 sunscreen for the same damage to occur it would take 500 minutes. “Now how can they say to people that we are not going to tell you that you could get that kind of protection.”

The cancer authorities have not allowed numbers over 15 to be put on sunscreens for a number of reasons. Firstly, they are concerned that if they allow the actual numbers to be put on the sunscreens, manufacturers will be forced to compete with each other to get higher and higher numbers on their sunscreens to attract customers and they are worried that it will just become a numbers game. Greenoak suggests that it is a numbers game in the consumers interest.

Secondly there is a health concern. If there are sunscreens on the market with high SPF numbers people will think that they can spend longer in the sun which is not a good idea. Although they may be able to spend longer in the sun without getting sunburnt scientists are not sure that they can safely spend this time in the sun without a risk of getting skin cancer, because so not enough is known about how skin cancer is caused. It may be that a person can get skin cancer without getting sunburned. “Every individual has their own meter if you like, the red light comes on when you, specifically you, have had too much sunlight,” says Greenoak. “You will feel it before you actually see it and you will move out of the sun. When you put a sunscreen on you switch off that little signal. But you don't need to produce the redness you see to get skin cancer. So this gets to be a bit of a worry.”

Thirdly, there has been some concern about the active UV absorbing chemicals in sunscreens and they have had to be used in increasing amounts to achieve higher SPFs. However the technologies for making sunscreens have become highly sophisticated and there are now a number of other ways of achieving high protection without increasing the concentrations of the active ingredients. Some sunscreens on the market have neither of the two most widely used active chemicals in them at all and the use of titanium and zinc particles is becoming increasingly popular.

It has been known for a long time that the shortest wavelengths of UV light penetrating the atmosphere, known as UVB, cause redness, sunburn and skin cancer, but more recently it has been clearly shown that longer wavelengths known as UVA contribute to these effects and may be a major cause of skin damage. Many sunscreens are now becoming broad spectrum. Their manufacturers claim that they not only filter UVB light like ordinary sunscreens but also UVA light. The problem is that UVB and UVA are arbitrary divisions of the continuous sunlight spectrum and the UVA which does contribute to the UVB effects is almost certainly tested for already with the solar simulator which also has a continuous spectrum.

UVA has recently been further divided into UVA-2 at the short end, and UVA-1 at the long end. Long wavelength UVA-1 which is what you will get through ordinary untinted window glass is very much less effective in producing sunburn than UVB which makes testing protection from it rather difficult. Whereas researchers can look for sunburn when they are testing for UVB protection there is no such simple test for UVA protection. So the only test that can be done is a spectrophotometric test which involves using a spectrophotometer to measure how much UVA light comes through a sunscreen. “If that was adequate” Greenoak points out, “that is what one would do for the UVB too, but we know it's not. A sunscreen will always interact with the skin surface in a way which is important for its protectivity”

It is because of all of these concerns that the State Cancer Council's in Australia have erred on the side of the conservative ceiling of 15+. Sunscreen protection is a complex matter and people like Greenoak argue for the urgency of doing more research. “There are many questions that only long term research on humans and mice will really be able to determine and given the incidence of skin cancer in this country and its certain exacerbation by ozone depletion, the research is well nigh crying out to be done so that we can answer some of these questions.”