Bill Tuthill wrote:
Mike Romain wrote:

Does anybody find that there is a huge difference in effectiveness
between SPF 15 versus 40 sunblock?

One allows 1/15 of the UVB to pass, the other allows 1/40 of the UVB.

Yes, a huge difference.
I live in Canada and we are affected by the ozone hole here.
The local weather and newspapers give the ozone index every day.

The index is given everywhere. I don't know if the northern hole
affects anywhere but northern Canada--does anyone have a map of the
approximate dimensions?

Usually I wear clothing, which depending on fabric, works very well.
One day rafting I used SPF 40 instead, reapplying every time my legs
got wet, which was about every hour. Got a mild sunburn.

Some fabrics are surprisingly low, such as the old dress shirts that I
often use as a top layer in the sun or bugs.

Does the expiration date make a large difference in the efficacy of
certain sunblock chemicals? This SPF 40 was about a year past expiry,
although it contained titanium dioxide and zinc oxide, two ingredients
that I doubt degrade rapidly.

You are probably right. We just use the stuff until it is done. The
older bottles get sed up as daily kids-wear at home and/or in the car.

GaryJ

In rec.backcountry Bill Tuthill wrote:

Usually I wear clothing, which depending on fabric, works very well.
One day rafting I used SPF 40 instead, reapplying every time my legs
got wet, which was about every hour. Got a mild sunburn.

There is a product called 'Sun Guard' for increasing protection from the sun
through clothing. You put some in the washing machine when washing the
garment you wish to treat.

GaryJ wrote:

Bill Tuthill wrote:
Mike Romain wrote:

Does anybody find that there is a huge difference in effectiveness
between SPF 15 versus 40 sunblock?

One allows 1/15 of the UVB to pass, the other allows 1/40 of the UVB.

Yes, a huge difference.
I live in Canada and we are affected by the ozone hole here.
The local weather and newspapers give the ozone index every day.

The index is given everywhere. I don't know if the northern hole
affects anywhere but northern Canada--does anyone have a map of the
approximate dimensions?

Hard to find and updated stuff seems to be 'hiding' for some reason...

Here is the data from 79 to 98:
http://jwocky.gsfc.nasa.gov/multi/TOMSmarch79_98.gif

from this link:

http://jwocky.gsfc.nasa.gov/multi/multi.html

It looks like it even tags the USA, let alone Canada.

A friend of ours was monitoring some ozone instruments in the far north
and he said folks would be scared silly if they knew how big the
northern one was. Then the government shut down the stations a couple
years ago, so as far as I know nothing from the ground is monitoring it
at all now.


Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's