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sunscreen makes you hotter?



 
 
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  #1  
Old July 31st 03, 02:33 PM
larry english
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Default sunscreen makes you hotter?

i was wondering how sunscreen works.

about all i can find out is that it seems to trap and absorb the uv
radiation before it gets to your skin.

but the heat from absorption still does.

so my question is, wouldn't that make you hotter than not using sunscreen?

or is it the same, i.e., if you weren;t using it, the skin would
absorb the uv anyway...?

seems like it would be better to invent a sunscreen that would
reflect the uv away, rather than absorb it.

wle.
Ads
  #3  
Old July 31st 03, 08:05 PM
Bill Davidson
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Default sunscreen makes you hotter?

Bob Denton wrote:
UV doesn't make you hot. It's infra red and visible light.


I'm pretty sure that's not true. Any time you absorb radiation,
you get heat. In other words, they all make you hot. It's
possible that UV results in less heat but even that I doubt.

Why does UV filtering (tint) on windows reduce the heat buildup
inside a car or building; even if it's a very light tint?

--Bill Davidson
--
Please remove ".nospam" from my address for email replies.

I'm a 17 year veteran of usenet -- you'd think I'd be over it by now

  #4  
Old July 31st 03, 09:40 PM
Tim McNamara
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Default sunscreen makes you hotter?

In article eMdWa.33166$Ne.31813@fed1read03,
Bill Davidson wrote:

Bob Denton wrote:
UV doesn't make you hot. It's infra red and visible light.


I'm pretty sure that's not true. Any time you absorb radiation,
you get heat. In other words, they all make you hot. It's
possible that UV results in less heat but even that I doubt.


If all radiation absorption results in heating equally, why don't
microwaves use UV frequency light and use radio waves instead?

From www.howstuffworks.com:

A microwave oven uses microwaves to heat food. Microwaves are radio
waves. In the case of microwave ovens, the commonly used radio wave
frequency is roughly 2,500 megahertz (2.5 gigahertz). Radio waves
in this frequency range have an interesting property: they are
absorbed by water, fats and sugars. When they are absorbed they are
converted directly into atomic motion - heat. Microwaves in this
frequency range have another interesting property: they are not
absorbed by most plastics, glass or ceramics. Metal reflects
microwaves, which is why metal pans do not work well in a microwave
oven.


UV light only penetrates the skin about 1 mm, but this is deeper than
visible light penetrates. This is where the basal layer of the skin
is found (and where basal cell carcinomas start). Much of the visble
light spctrum is simply reflected from the skin and is not absorbed.
Sunscreen places an absorptive barrier specific to UVa and UVb
radiation above the skin, so it is absorbed or blocked before it gets
to the skin.

The shorter the wavelength, the more energy light has. Therefore UV
has more energy than visible light. As the wavelength of
electromagnetic radiation decreases, the radiation can be more
penetrative and damaging to living tissue (X rays and gamma rays).
These are not as readily absorbed by tissue and cause less heating as
a result. X rays pass through soft tissue readily, but tend to be
absorbed by bone, and can be captured on photographic film. Gamma
rays pass through hard tissue as well (and thus tend to be destructive
of bone marrow, for example).

Longer wavelengths such as microwaves and radio waves are more
absorbable (sp?), hence their use in microwave ovens to heat food.

Why does UV filtering (tint) on windows reduce the heat buildup
inside a car or building; even if it's a very light tint?


I suspect- but don't know- that heat gain through a transparent
surface such as window glass, with subsequent heating of the air
volume enclosed by the windows, is a matter of different wavelengths
than is the case with skin. Air absorbs different frequencies of
light and refiects none, unlike skin. Ditto the metal of a car body,
the brick of a wall, or the fibers of upholstery.

UV tinting is primarily used to prevent fading of upholstery and
doesn't- by itself- result in much reduction of solar (heat) gain
because the other frequencies are selectively unfiltered. Just as in
the case of UV photographic filters, which are nearly colorless, UV
tinted auto glass serves to improve long-distance vision by filtering
at the blue end of the visible spectrum. Blue light scatters more
easily in Earth's atmosphere than the longer wavelengths, causing
blurring of vision.

We probably see the small portion of the electromagentic spectrum that
we do because a broader spectrum could not be focused on the retina as
well. Even within the range of frequencies we can visually perceive,
the focal length for the short end of the visible spectrum is slightly
different than the focal length for the long end.

As far as sunscreen making one feel hotter- my subjective impression
is that I feel hotter with sunscreen on. I suspect this is due to the
oil base that most sunscreens use, which reduces the "wind chill"
effect and puts an insulating layer between the skin and the sweat as
it evaporates. My skin is certainly much wetter with sweat when I
wear sunscreen.
  #5  
Old July 31st 03, 10:39 PM
Terry Morse
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Default sunscreen makes you hotter?

Tim McNamara wrote:

If all radiation absorption results in heating equally, why don't
microwaves use UV frequency light and use radio waves instead?


snip

UV light only penetrates the skin about 1 mm,


You answered your own question: UV doesn't penetrate much and would
only heat the outer surface of the food. A kilowatt of UV would
transfer the same energy to the food as a kilowatt of microwave, but
the microwave would heat deeper.
--
terry morse, heat transfer specialist
  #6  
Old July 31st 03, 11:11 PM
Øyvind Røtvold
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Default sunscreen makes you hotter?

Tim McNamara writes:

[snip]
If all radiation absorption results in heating equally, why don't
microwaves use UV frequency light and use radio waves instead?


A fair question.

[snip]
UV light only penetrates the skin about 1 mm,


And there is the answer.

[snip]



The shorter the wavelength, the more energy light has.


Nope, The shorter the wavelength, the more energy per photon The
amount of energy in a wave depends on ... the amount of energy in the
wave.

[snip]

Longer wavelengths such as microwaves and radio waves are more
absorbable (sp?), hence their use in microwave ovens to heat food.


IR waves will be absorbed in the outer layer of food, hence their use
in barbeque.

[snip]
As far as sunscreen making one feel hotter- my subjective impression
is that I feel hotter with sunscreen on. I suspect this is due to the
oil base that most sunscreens use, which reduces the "wind chill"
effect and puts an insulating layer between the skin and the sweat as
it evaporates. My skin is certainly much wetter with sweat when I
wear sunscreen.


Sweat will not evaporate as fast from a oily surface.

--
__o | Øyvind Røtvold
_`\(, | http://www.darkside.no/olr/index.html
(_)/(_) | ... biciclare necesse est ...
  #8  
Old August 2nd 03, 03:59 PM
g.daniels
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Default sunscreen makes you hotter?

adequate heat transfer from the body to the environemnt requires
radiators-the capillary network below the basal layer does this and a
skin layer mechanism.Different areas of your skin transmit varying
quantities of heat-the head throws of a lotta heat that comes from the
metabolic processes that drive your muscles ect.

"My skin is certainly much wetter with sweat when I
Ø wear sunscreen. UV doesn't make you hot. It's infra red and visible
light
Any time you absorb radiation,
Ø you get heat. In other words, they all make you hot.
www.howstuffworks.com:"

and this is all true but clogging the pores with sunscreen??? probably
cuts down on that areas heat transfer efficiency while reducing heat
absorption-all those photons banging the devil outa your chromosomes
and cuasing melanoma. which incidentlly increases with age and with
the wind burn effect fron cycling which sunscreen reduces especially
on the shins.

But the deal is that one only rubs the sunscreen on some body parts
not all and the other parts take up some of the slack.
if you're having problems with heat transfer then one might look at
psychologic quantifications of the problem over time-like eating
oatmeal before may mae you hot when eating bananas doesn't rather than
the sunscreen.
The botttom line(and try a split seat there) is conditioning for the
heat. ya gotta run run run in the heat to not be too hot. taking a
pill doesn't do it.
wqearing a wicking skull cap with clean short hair might help, wicking
socks and surely an adnaced textiles wicking t-shirt the more
expensive the better and if you're in AR going east at 3pm try an arab
neck scarf. and try coppertone.
  #9  
Old August 2nd 03, 04:06 PM
g.daniels
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Default sunscreen makes you hotter?

color equals colr not heat!
neutrinos pass thru everything, see the Antarctic neutrino telescope
facing into the earth from an ice bed. (the possibilities of a deep
space tunnel emitting these particles with an eddy layer?)
 




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