Solar Injury and Sunscreen Preview

Solar Injury (Part 1) See the handout section on the right to view the complete document.

1) my dermatologist tells me I should never be exposed to the sun. Is solar radiation all bad?
Clearly no. Without infrared radiation - we would freeze to death. Without light, we would all starve, by viture of having no plants to eat. Finally, without UV radiation causing Vitamin D production we would get rickets and increased levels of cancers.

2)What are the three relevant kinds of Ultraviolet radiation (UVR) of importance to humans?
UVR comes in 3 flavors. The first UVC, has the shortest wavelengths, and therefore the greatest energy, measuring 200 - 290 nanometers. UVC is of importance only where the protective ozone layer has been destroyed, e.g. arctic regions and extreme southern Chile and Argentina. Elsewhere, UVC is entirely absorbed in the stratosphere by ozone and oxygen.

UVB measures (290-320nm) and is responsible for Vitamin D production from 7-dehydroxyxholesterol, vias the skin, liver and kidney. UVB is also responsible for tanning, burning and skin cancers, though not melanoma.

UVA has longer wavelengths (320 - 400), and contributes to photoaging, tanning, burning, and some skin cancers. UVA also triggers phototoxicity of certain pharmaceuticals.

3) What environmental features most affect the amount of UVA and UVB that reaches the skin?

Time of day: 65% between 10a and 2p, but with daylight savings all bets are off!
Season is important. June has 100x more UVR than December
Latitude: 3% decrease with every degree of latitude from equator. Albuquerque 35 degrees N, Taos is 36.
UVA varies less with daytime and latitude changes - scatters less than shorter wavelength UVB.

Surface features: water reflects small amount of UVR. Snow reflects much more. (85%).

Clouds - attenuate UV radiation by 20-80% - generally 40%. Better absorber of IR radiation (heat).

Altitude: 10% increase with every 1000 feet elevation. Wind exacerbates solar damage - erythema- of skin. Moisture increases dermal absorption of UVR.

Pollution increases absorption of UVR through particulates and ozone.

Bottom line: Taos Ski Valley in March is a site of plenty of UVR! So slather up with sunscreen and don't forget those sunglasses! (I speak from personal experience)....

To read more:
Part 1 and Part 2 of the handout references are permanently posted in the "Handout" sections.

Joe Alcock