# Water droplets, sun and skin cancer **URL:** \ **Category:** Factual Questions\ **Created:** [September 18, 2009, 11:23am UTC](https://boards.straightdope.com/t/water-droplets-sun-and-skin-cancer/510576 "2009-09-18T11:23:36Z")\ **Posts on this page:** 9\ **Page:** 1
**Author:** ![Colophon](https://avatars.discourse-cdn.com/v4/letter/c/f05b48/32.png) [@Colophon](https://boards.straightdope.com/u/Colophon)\ **Post date:** [September 18, 2009, 11:23am UTC](https://boards.straightdope.com/t/water-droplets-sun-and-skin-cancer/510576/1 "2009-09-18T11:23:36Z")
When I was lying on the beach after swimming the other day (on a rare hot and sunny day), i noticed that I still had drops of water on my skin in places. I also noticed that they seemed to be focusing the sun’s rays like a lens, which got me thinking - this can’t be good, right? I don’t recall ever hearing anything about this but it stands to reason that water drops might be able to focus UV rays down to create “hot spots” of skin damage. Should we be worried about this? ---
**Author:** ![Philster](https://avatars.discourse-cdn.com/v4/letter/p/13edae/32.png) [@Philster](https://boards.straightdope.com/u/Philster)\ **Post date:** [September 18, 2009, 12:28pm UTC](https://boards.straightdope.com/t/water-droplets-sun-and-skin-cancer/510576/2 "2009-09-18T12:28:56Z")
I never got a spotted burn from water droplets. I have never observed droplet burns. Based on my observations, water reflects and refracts some light (visible light), but I can’t speak for the UV part. However, lacking any droplet burns, I conclude that droplets do not do any 'magnifying". Maybe a random droplet has some odd physical properties that result in a concave shape that has the potential to focus and/or magnify the rays (doubt it). ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [September 18, 2009, 1:10pm UTC](https://boards.straightdope.com/t/water-droplets-sun-and-skin-cancer/510576/3 "2009-09-18T13:10:21Z")
As the first chart on [this page](http://people.seas.harvard.edu/~jones/es151/gallery/images/absorp_water.html) shows, water strongly attenuates UV radiation (UV wavelengths are in the 10-400nm range). A droplet thick enough to do a decent job of focusing is thus probably passing only a small percentage of the UV it receives. ---
**Author:** ![Philster](https://avatars.discourse-cdn.com/v4/letter/p/13edae/32.png) [@Philster](https://boards.straightdope.com/u/Philster)\ **Post date:** [September 18, 2009, 1:22pm UTC](https://boards.straightdope.com/t/water-droplets-sun-and-skin-cancer/510576/4 "2009-09-18T13:22:11Z")
attenuation (in some contexts also called extinction) is the gradual loss in intensity through a medium ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [September 18, 2009, 1:32pm UTC](https://boards.straightdope.com/t/water-droplets-sun-and-skin-cancer/510576/5 "2009-09-18T13:32:10Z")
> [@Philster](#): > > attenuation (in some contexts also called extinction) is the gradual loss in intensity through a medium Well, it can be gradual or quite rapid, depending on the medium and the wavelength. ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [September 18, 2009, 3:46pm UTC](https://boards.straightdope.com/t/water-droplets-sun-and-skin-cancer/510576/6 "2009-09-18T15:46:44Z")
> [@Xema](#): > > As the first chart on [this page](http://people.seas.harvard.edu/~jones/es151/gallery/images/absorp_water.html) shows, water strongly attenuates UV radiation (UV wavelengths are in the 10-400nm range). A droplet thick enough to do a decent job of focusing is thus probably passing only a small percentage of the UV it receives. That chart is showing that the great majority of tanning rays WOULD make it through more than 1 cm of water. ---
**Author:** ![Philster](https://avatars.discourse-cdn.com/v4/letter/p/13edae/32.png) [@Philster](https://boards.straightdope.com/u/Philster)\ **Post date:** [September 18, 2009, 4:05pm UTC](https://boards.straightdope.com/t/water-droplets-sun-and-skin-cancer/510576/7 "2009-09-18T16:05:58Z")
The issue at hand is whether the droplets of water would magnify (focus) the rays increasing the risk of hot spots on the skin, potentially causing damage. The answer seems to be “no”. ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [September 18, 2009, 4:11pm UTC](https://boards.straightdope.com/t/water-droplets-sun-and-skin-cancer/510576/8 "2009-09-18T16:11:55Z")
> [@Napier](#): > > That chart is showing that the great majority of tanning rays WOULD make it through more than 1 cm of water. I disagree. The 10nm part of the chart is at the extreme left, where the absorption coefficient is really high and the penetration depth is really low. It’s true that at the longer UV wavelengths the absorption is dropping significantly, but these are the much less harmful frequencies. ---
**Author:** ![Tastes\_of\_Chocolate](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tastes_of_chocolate/32/3232_2.png) [@Tastes\_of\_Chocolate](https://boards.straightdope.com/u/Tastes_of_Chocolate)\ **Post date:** [September 18, 2009, 6:15pm UTC](https://boards.straightdope.com/t/water-droplets-sun-and-skin-cancer/510576/9 "2009-09-18T18:15:49Z")
Are the wavelengths that cause suntan/burn the same ones that darken photo grey glasses? personal experience - If I have a drop of water on my photogrey eyeglasses, the glass behind the water does not darken nearly as much as the rest of the glass. I will have a pale spot. So if it’s the same wavelengths, then the water seems to block more then it magnifies.