[neilep (OP)]

Hi There,
Phew !..a hot day for me here in the UK !...I can't take heat !!..so....

How Does Sun Screen Cream work ?

Does it just block UV rays ?..or does it block other rays too ?.....How does it do it?......what happens to the UV rays that hit it ?...do they get reflected ?..absorbed ?

And does it need re-applying because it gets absorbed by the skin or that it loses it's effectiveness after a while ?

...I'm mainly interested in HOW it protects ?

Thanking ewe.

[lyner]

It amazes me that such a thin layer ha a chance of protecting anything. If the cream was black and you spread it over your skin , patches of skin would be visible, I'm sure. This implies that it is far 'more opaque' to UV than the  black pigment  in the cream would be to visible light. Of course, the wavelength of UV is less, so the thickness of any layer in wavelengths would be more for UV. More chance for absorption.
In both cases, the energy of the radiation would be transferred to thermal energy which is harmless -  just gets you warm.

[lightarrow]

http://health.howstuffworks.com/sunscreen4.htm

[neilep (OP)]

THANK YOU SOPHIECENTAUR & THANK YOU ALBERTO for the link..

That covers it !!..LOL []

For this who are interested and just can not be bothered to click the link  to the How It Works site.I have copied and pasted it just for you here...honestly..I'm just too good !!



Sunscreens

Sunscreens block or absorb ultraviolet light. You can block UV light with opaque creams like the white zinc oxide cream that you see lifeguards putting on their noses. You can also absorb UV radiation in much the same way that melanin does. The first and most common of the absorption chemicals is PABA (para-aminobenzoic acid). It absorbs UVB. If you have sensitive skin, take care when using sunscreen with PABA as it may cause irritation or an allergic reaction in some individuals. Other sunscreen chemicals include:

    * Cinnamates absorb UVB.
    * Benzophenones absorb UVA.
    * Anthranilates absorb UVA and UVB.
    * Ecamsules absorb UVA.

All sunscreens are labeled with an SPF, or Sun Protection Factor. The SPF acts like a multiplying factor. If you would normally be OK in the sun for 10 minutes and you apply an SPF 10 sunscreen, you will be OK in the sun for 100 minutes. In order for the sunscreen to work, however, you have to apply plenty and it has to stay on. You should apply it about half an hour before going out in the sun (or the water) so it can bind to your skin -- if you don't, then it is very easy for the sunscreen to wash off.

The SPF rating, by the way, applies only to UVB radiation.

[Alandriel]

I know it's November and unless you're living in the southern hemisphere, have booked a longhaul flight (naughty! lucky!!!)or are heading for the high mountains you're not very likely to get some sunshine....

BUT.... I came across this interesting little titt-bitt and since it involves my national flower I could not resist:


Want to protect yourself from sun damage? Slathering yourself in edelweiss could help *)

Edelweiss is a mountain flower and so is exposed to a large amount of ultraviolet light. Just how it protects itself from tissue damage at such high altitudes has been a mystery, says Jean Pol Vigneron at the University of Notre-Dame de la Paix in Namur, Belgium.

Vigneron and his colleagues measured the spectrum of light reflected from the plants and found that while most wavelengths are reflected, UV is not. "It's astonishing, but the plant completely absorbs the UV," says Vigneron.

The team then examined the tiny, white hairs that cover edelweiss leaves under a scanning electron microscope. They found that the hairs are made up of parallel fibres 0.18 micrometres across, which is close to the wavelength of UV light. This means they can interact with UV light, steering it along the length of the leaves, says Vigneron. In this way, the UV light is absorbed over a large number of hairs instead of penetrating to the plant's body (www.arxiv.org/abs/0710.2695)
The trick should be exploited to create a 'natural' sunscreen for people. We currently use unscreens made of titanium dioxide particles, but these can be absorbed through the skin and can be harmful, says Vigneron.

New Scientist article

*) footnote by me: edelweiss is under protection in Switzerland (and probably other alpine countries) - don't get any ideas. Use the readily available potted variety  []

[Bass]

so if we all grew lots of tiny white hairs and ended up looking like sasquatch (actually, I've never seen a sasquatch)- we'd be safe from skin cancer? []