DrPeter

I just purchased a 1997 993 targa. As a dermatologist, I am interested if porsche provides both UVA (cancer causing) and UVB ( sun burning) protection in their tinted glass. I tried contacting sequrit, the company that manufactures the glass, but they did not reply. Does anyone know how to find the answer to this question? DrPHelton@aol.com

Pierre

Peter,

The latest Christophorus (got it yesterday, talk about coincidence!) has an article about the glass Porsche's using and how it's manufactured. The windshield is said to offer 100% UV-protection. No mention of UVA/B, just UV in general.

Greetings,
--Pierre

Danno

Hmmm, by its nature, glass will block UV rays: <a href="http://www.howstuffworks.com/question404.htm" target="_blank">http://www.howstuffworks.com/question404.htm</a>

Some more interesting links:

• <a href="http://www.ccohs.ca/oshanswers/diseases/skin_cancer.html" target="_blank">http://www.ccohs.ca/oshanswers/diseases/skin_cancer.html</a>
• <a href="http://www.ciesin.org/docs/001-561/001-561.html" target="_blank">http://www.ciesin.org/docs/001-561/001-561.html</a>
• <a href="http://www.photobiology.com/UVR98/wongrev/index.htm" target="_blank">http://www.photobiology.com/UVR98/wongrev/index.htm</a>
• <a href="http://www.birchtrees.com/issunenharhe.html" target="_blank">http://www.birchtrees.com/issunenharhe.html</a>
• <a href="http://www.hawaiiantan.com/qvc.htm" target="_blank">http://www.hawaiiantan.com/qvc.htm</a>
• <a href="http://www.ccohs.ca/oshanswers/diseases/skin_cancer.html" target="_blank">http://www.ccohs.ca/oshanswers/diseases/skin_cancer.html</a>
• <a href="http://www.skincancerinfo.com/sectiong/sunscreens.html" target="_blank">http://www.skincancerinfo.com/sectiong/sunscreens.html</a>
• <a href="http://www.beachpeople.com/sunprotection101.html" target="_blank">http://www.beachpeople.com/sunprotection101.html</a>
• <a href="http://www.nsc.org/ehc/glossar2.htm" target="_blank">http://www.nsc.org/ehc/glossar2.htm</a>
• <a href="http://www.amazingbluereptiles.com/Care_and_Breeding.htm[/list" target="_blank">http://www.amazingbluereptiles.com/Care_and_Breeding.htm</a>

Seems to indicate both UVA & UVB causes damage with UVB being the main culprit in skin cancer.

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While broad-spectrum sunscreens exist, it's interesting to note that the SPF rating applies only to UV-B:

"UVB is most pronounced midday, does not penetrate window glass, and is associated with sunburn...SPF ranges from 1-45 or above and quantifies UVB protection. (8) A sunscreen with SPF 15 filters 92% of the UVB...(9) There is currently no uniform measure for UVA absorption." - <a href="http://www.acpm.org/skinprot.htm" target="_blank">http://www.acpm.org/skinprot.htm</a>



Same thing with sunglasses:

"Ultraviolet radiation is divided into two major bands, UV-A and UV-B. UV-A is longer wavelength radiation, close to blue in the visible spectrum, that usually induces skin tanning and browning, and has been implicated in skin aging. UV-B is more active, shorter wavelength radiation that causes blistering sunburn and is associated with skin cancer.... there is no present standard of labelling that adequately indicates UV-A or blue protection. " - <a href="http://www.alberta-retina.com/sunglass.htm" target="_blank">http://www.alberta-retina.com/sunglass.htm</a>

DrPeter

Ordinary glass will block UVB;"the sun-burning rays," but not UVA which are aging and skin cancer rays." This is exemplified by noticing as we get older there are more wrinkles and skin cancers on the left sides of our faces because that is where the light comes in through the windshield as we drive. Years ago when SPF ratings were developed, we did not think UVA was important, because the effects of it did not become apparent until 10-20 years later. Now we know better. If something says it has UV protection, it does not always mean it protects you from BOTH UVA & UVB, it may only protect you from one. This is also true of sunscreens and sunglasses.

DrPeter

Blistering sunburns also increase your chances of skin cancer, especially melanoma. It is true that both UVB and UVA radiation will cause cancer, but most experts believe that UVA is worse. Prolonged UVB results in a burn, so you get out of the sun. That is not as true for UVA, which burns 1/10th as much as UVB. It is kind of scary because UVA is what most tanning beds use.

Anir

Peter,

Nice summary. I'm also a dermatologist, and ironically, just finished giving an academic presentation on skin cancer and sunscreens earlier today.

Unfortunately, I strongly suspect that we have only seen the "tip of the iceberg" with respect to tanning bed / UVA-induced skin cancer. My skin cancer patients are getting younger and younger by the year.

Danno

Drs. Peter & Anir, could you elaborate on the wavelengths we're talking about when you refer to UVB & UVA? I'm reading conflicting results from studies here. Also are there any evidences of the dangers of UVC (UVR) which are even higher-frequency rays that supposed are blocked by the ozone layer?

Anir

Danno,

UVA 320 - 400 nm: Emitted by tanning beds, and one-tenth of the UV radiation in natural sunlight that reaches the earth's surface

UVB 290 - 320 nm: Primary component of natural sunlight (90%)

UVC 100 - 290 nm: Largely absorbed by earth's atmosphere before reaching the earth's surface (and therefore, less of an issue to humans)

As Peter nicely explained, both UVA and UVB cause skin cancer, although we did not appreciate the causative role played by UVA until relatively recently. There is signficant evidence to suggest that UVA causes "photoaging" of the skin (ie. wrinkles, leathery changes, broken blood vessels, etc) more effectively than UVB.

Therefore, tanning beds are a double whammy - skin cancer and aging at a rate potentially faster than natural sunlight (which is bad enough). A recent study suggests that tanning bed users are 1.5 times more likely to develop basal cell carcinoma and 2.5 times more likely to develop squamous cell carcinomas.

Here are some other nice links (in addition to yours) for further info:

<a href="http://sunshine.jpl.nasa.gov/1rst%20Tier/References/VITAL.TECH.UV.html" target="_blank">NASA</a>

<a href="http://www.fda.gov/fdac/features/2000/400_sun.html" target="_blank">FDA</a>

Another interesting factoid that is not appreciated by many folks:

UVB blocked
SPF 15 93.0%
SPF 30 96.7%
SPF 40 97.5%
SPF 70 98.6%
Therefore, a sunscreen with an SPF 50 is not three times as effective as one with an SPF 15!

As a result, the FDA has mandated that all sunscreen manufacturers limit SPF claims to no higher than "30+" starting 1/1/03.