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[UV SAFETY] UV and Your Eyes :: UV Safety Reference

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#1 Andrea B.

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Posted 06 November 2015 - 16:19

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Last Edit [8 Nov 2015 1:23 PM UTC -5]

UV Eye Damage

Question: I would like to photograph someone with their eyes open. It is widely warned that you should not look directly into a uv flash or LED, however, what if you did?

UV-blocking eye protection in the form of UV-blocking goggles or face masks is mandatory when using any UV outputting lamp, bulb, flash, LED light or other device. This includes those UV "party" lights, also used for fluorescent posters.

No one can tell you how many UV-flashes are "too many" for human eyes because those experiments are not done on human subjects. So, the simple answer is do not flash UV into anyone's eyes or expose your own eyes to UV outputting devices. Here is what could potentially happen short-term and long-term.

Short term exposure to intense UV causes ultraviolet keratitis, a photochemical injury to the cornea of the eye. Welders call this welder's eye and skiers call it snowblindness. In mild cases, you feel dry, scratchy eyes, some eye pain, sensitivity to light and have reduced vision for a few hours because your cornea is swollen and inflamed. This injury is often referred to as a flash burn or a corneal burn, but it is not thermal in nature even though it feels like it.
In severe cases of UV keratitis, there can be corneal ulceration and possible infection. Severe corneal damage might eventually necessitate a corneal transplant (taken from a cadaver).
Sources: halogen lights, carbon arcs, welding arcs, sunlight on snow, sunlight on water, UV flashes, photo floodlights, sun lamps, tanning beds.
Protection: UV-block goggles, welder's mask.
Ultraviolet Keratitis This is a medical monograph by Reed Brozen, MD of Dartmouth Medical School, Dartmouth-Hitchcock Medical Center written with various co-authors.
Corneal Flash Burns

Long term exposure to UV from sunlight or other sources causes cumulative damage to the human eye which typically manifests itself as the formation of cataracts. A cataract is a cloudy deposit on or within the eye lens. It is said that sooner or later we all get cataracts. This is why ophthamologists encourage everyone to wear UV-blocking sunglasses when outdoors. Long term exposure to UV in sunlight or from other sources can also cause retinal damage or eye cancers.
These links about cataracts and UV are from the US National Institute of Health:
Facts about Cataract
New research sheds light on how UV rays may contribute to cataract


UV Exposure Recommendations

The Columbia University (New York City) monograph Working Safely with Ultraviolet Radiation contains some UV exposure recommendations.

Columbia notes that in the United States there is no Occupational Safety and Health Administration (OSHA) standard for exposure to ultraviolet light. OSHA is a federal agency (in the US Department of Labor) which enforces safety & health laws.
The National Institute for Occupational Safety and Health (NIOSH), part of the US Center for Disease Control and Prevention, does make some recommendations.
Also, the American Conference of Governmental Industrial Hygienists (ACGIH) has issued Threshold Limit Values (TLVs) for occupational exposure to UV.

I have to review notation here so I can keep it straight.
watts = W
milliwatts = mW
microwatts = µW
1W = 103mW = 106µw

meters = m
centimeters = cm
1m2 = 104cm2

Columbia Recommendation for UVA Wavelength Range 315 - 400 nm: 10 Watts/m2 for every 1000 seconds
i Total irradiance on unprotected eyes and skin for periods of greater than 1000 seconds should not exceed 10 Watts/m2.
ii Total radiant exposure on unprotected eyes and skin for periods of less than 1000 seconds should not exceed 104 Joules/m2.

ACGIH Recommendation for UVA Wavelength Range 315 - 400 nm: 1 milliWatt/cm2 for every 1000 seconds
The maximum time of unprotected exposure to an intensity of 1 milliWatt per square centimeter in the UV range should not exceed 1000 seconds.
This is the same as the preceding Columbia recommendation.

Convert: 10 Watts/m2 = 1 milliWatt/cm2
So the ACGIH recommendation is, of course, the same as the Columbia recommendation.
Convert: 1 milliWatt/cm2 for 1000sec == 1000 milliWats/cm2 for 1 second.

Columbia Recommendation for UVB Wavelength Range: 200 - 315 nm
The radiant exposure on unprotected eyes and skin within any 8 hour period is limited to values which depend on the wavelength of the radiation. For a broadband source the effective irradiance should be measured or calculated and the maximum permissible exposure determined from the table below.
Effective Irradiance (Watts/m2) <==> Maximum Permissible Exposure during an 8 hour period
0.001 <==> 8 hours
0.008 <==> 1 hour
0.05 <==> 10 minutes
0.5 <==> 1 minute
3 <==> 1 second
30 <==> 0.1 second

NIOSH Recommendation for UVC 254 nm: 100μW/cm2 for 1 minute
The maximum time of unprotected exposure to an intensity of 100 microWatts per square centimeter at wavelength 254 nanometers should not exceed 1 minute.
When averaged over an eight-hour work day, this value is 0.2 microWatts per square centimeter.

Convert: 100microWatts/cm2 = 0.1milliWatts/cm2 for 1 minute.

Side Note: There is one mis-statement in this Columbia U. reference. They say eye damage is from UV-B and UV-C, but it has been recently learned that eye damage also occurs due to oxidative stress from UV-A. See Ultraviolet Keratitis link above.

Example: Blak-Ray B-100 AP Lamp

From the manufacturer's data, we have that the Blak-Ray B-100 AP lamp with a UVA range peaking around 365 nm delivers an intensity of 21.7 milliWatts/cm² at 5 cm and 8.9 milliWatts/cm² at 25 cm (about 10") distance from the lamp.

Various factors affect the actual intensity from such a lamp because of geometry, angles of use, ambient reflections and so on. Nevertheless, we will use those numbers in the following model as a worst-case intensity from a Blak-Ray directly shining on a subject.

Given that the Columbia or ACGIH recommendation for UVA is 1000 milliW/cm2 for 1 second, we can convert: 1000/8.9 = 112 seconds = 1.87 minutes.

So, you have a little under 2 minutes of time to have unprotected UV-light with your Blak-Ray B-100 lamp
at a distance of 25 cm (10") within an 8-hour day.

If you have the Blak-Ray shining directly on yourself at the closer distance of 5 cm (2"),
then you only have a recommended exposure time of 46 seconds within an 8-hour day.

Wear your UV-blocking goggles.
And remember that even if you escape UV keratitis on your cornea by having unprotected UV-light,
the UV damage to eyes and skin is cumulative.

Eventually UV-light will getcha if you don't protect yourself!
And now for a musical interlude: https://www.youtube....h?v=FYlYJ55miI0
Start at 52 seconds in.

Sunlight vs. the Blak-Ray B-100

Reference: Incoming Sunlight from NASA Earth Observatory

All radiation from sunlight is equivalent to an intensity of 1.36 kiloWatts/m2 at the distance from sun to earth.
That translates to 136 milliWatts/cm2 at the distance from sun to earth.
Convert: 1kW = 106mW milliWatts
Convert: 1m2 = 104cm2

Of course, this total solar irradiance figure must be modified by reference to geometry, angles, atmosphere and so on when used in any model. Nevertheless, we'll use the 136 milliWatts/cm2 in the following little analogy as a worst-case kind of intensity from a presumed directly perpendicular ray of sunlight hitting an arm on the ground.

At ground level sunlight consists of about 3% UV.
So, UV-in-sunlight has an approximate intensity of 4.08 milliWatts/cm2 at distance from sun to earth.
The Blak-Ray has intensity 8.9 milliWatts/cm2 at a distance of 25cm/10".

On a good strong sunny day, put your arm on the ground and a Blak-Ray about 25cm (10") away from it.
The Blak-Ray intensity is approximately twice as strong as the UV-in-sunlight reaching your arm.
8.9/4.08 = 2.18

If your Blak-Ray is 5cm (2") inches from your arm, then it is approximately 5 times as strong as the UV-in-sunlight reaching your arm.
21.7/4.08 = 5.3

UVC @ 254 nm vs. the Blak-Ray?

UVC @254nm <=> 0.1 milliWatts/cm2 for 60 seconds.
Blak-Ray <=> 8.9 milliWatts/cm2 for 112 seconds @ 25cm distance.

Convert UVC: 0.1milliWatts/cm2 for 60 sec = 6 milliWatts/cm2 for 1 second.
Convert Blak-Ray: 8.9 milliWatts/cm2 for 112 sec = 996.8 milliWatts/cm2 for 1 second @ 25cm distance.

So, we can say that UVC is 166 times stronger than a Blak-Ray within a 1 second interval.

Sunlight <=> 4.08 milliWatts/cm2 for X seconds @ sun-earth distance.
Convert Sunlight: 4.08 milliWatts/cm2 for X seconds = 4.08*X milliWatts/cm2 for 1 second @ sun-earth distance.
If we assumed the UV-in-sunlight was just UVA, then X = 245 seconds = 4.1 minutes .
Thus we have 1000.8 milliWatts/cm2 for 1 second @ sun-earth distance.
Can we say that UVC is 250 times stronger than Sunlight within a 1 second interval? That UVC rather serious stuff.


Whatever I'm missing here (aside from a few UV-fried brain cells), please let me know and I'll correct it.
Andrea G. Blum
Often found hanging out with flowers & bees.

#2 Bill De Jager


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Posted 08 November 2015 - 03:45

Andrea, "distance not given" should not matter. These recommendations should be for the amount of radiation received by the target surface. It's up to the user of these recommendations to either measure the UV flux directly at the effective distance, or else calculate the effective flux given the distance involved and the emissivity of the source. The latter may be tricky as I don't think that light modified by a curved mirror or a lens *necessarily* follows the inverse square law in all cases. I hope someone who knows more on this can chime in.
Studying the botany and plant geography of California and western North America for almost 50 years.

#3 Andrea B.

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Posted 08 November 2015 - 14:54

Bill, thank you for reading this!

I probably should not admit just how long it has been since I dealt with anything from the land of physics (very long time ago). Later the penny did drop, and I realized what you said about distance. In the referenced thread (How Much UV is Bad for Me), I noted that I was also unsure about application of inverse square law. And still am. :rolleyes:

My hope is that I have translated the Blak-Ray data acceptably according to the NIOSH & ACGIH rules so that any photographic user of UV-flash, UV-lamps and/or UV-LEDs gets the idea that eye protection is mandatory and skin protection useful for the UVA/UVB range.

Note: I am cleaning up the first post so that it reads more easily.
Andrea G. Blum
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#4 OlDoinyo


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Posted 09 November 2015 - 01:30

One complication is that different wavelength ranges carry different kinds of hazards. The shortest wavelengths have little penetrating power and produce damage primarily on outer surfaces (some cannot even penetrate far into film emulsion.) Longer wavelengths are more insidious because they penetrate to greater distances and are more able to do subsurface mischief. Short-wavelength visible light (<500 nm) is itself known to have ionizing potential and can contribute to skin aging and carcinogenesis, among other things.

#5 JCDowdy


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Posted 09 November 2015 - 16:26

As UVP's resident photobiologist and UV photosafety expert I have been meaning to open a posting on this topic and I apologize for not finding the time to take the lead on this. There are many variables to consider some of which are mentioned above and some of which I have commented upon from time to time.

In my profession I rely primary on the following organizations providing guidance and safety standards on optical radiation safety:
  • IESNA (Illuminating Engineering Society of North America) which has adapted and expanded the older ACGIH (American Conference of Governmental Industrial Hygienists) guidance. The IESNA is an ANSI accredited standards developer and their relevant work is published an an American National Standard in the multi volume ANSI/IESNA RP-27 series of Recommended Practice for Photobiological Safety.
  • CIE (Commission Internationale de l'Éclarage -or- International Commission on Illumination) Division 6 Photobiology and Photochemistry, has adopted much, but not all, of the IESNA work and has published jointly with the IEC (International Electrotechnical Commission) the international standard CIE S 009 / E:2002 / IEC 62471:2006.
The two most critical factors to consider for exposure to continuous sources are the spectral distribution and exposure dose. The spectral distribution, or spectral irradiance is considered against several weighting functions representing different spectral hazards. For eye and skin the UV risk from shorter UV wavelengths may be several orders of magnitude greater than from longer UV wavelengths. The exposure dose is of course a function of the power of the source and the exposure time. For pulsed sources, such as our modified photographic strobes the dose is a function of pulse duration and number of pulses within a certain time.

I am not yet prepared to offer formal recommendations on limits for photographing human subjects. However at this point I am strongly cautioning against use of modified strobes and continuous UV sources to photograph people who are without proper eye protection.

I will also caution UV photographers to be mindful of radiation reflected and scattered back upon themselves, especially when using modified strobes, continuous UVB and UVC (germicidal) lamps. A UVC lamp can injure within seconds, a UVB lamp within seconds to minutes and a UVA lamp in minutes to hours depending on exposure dose (power x time) so the use of proper shielding and preferably remote camera operation is advised and in some cases may likely be required.

#6 Andrea B.

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Posted 09 November 2015 - 17:20

John, thank you so much for this excellent commentary on UV photosafety.
I have taken the liberty to embolden two parts of your post so that readers "take it home" that UV light is dangerous.

In the UV Sticky, I am going to link to this topic.

FWIW, my personal opinion is that no UV photographer should be attempting to photograph with UV-C light.
Andrea G. Blum
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#7 colinbm


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Posted 09 November 2015 - 22:50

I have wanted to respond to this from the beginning........but this is the best I can do diplomatically....
Whatidiot would argue about personal safety, particularly your eyesight, then go & put someone else in danger of damaging their eyesight!

#8 Cadmium


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Posted 10 November 2015 - 01:32

John, How do you feel about the common variety black light? People often buy them to illuminate various things in homes, displays, parties, etc..
I have seen these illuminated for sale in stores. I have used them for UVA photography, and tested them with bandpass filters, and they emit a much wider and deeper range of UV than just 365nm,
mine strongly illuminates a 325BP10 band pass filter, and my entire range of UV bandpass filters upward.
These are readily available everywhere with no warnings about their use as far as I have seen, and I think most people consider them 'safe'.
I have one here in front of me, a compact fluorescent type, purchased at a hardware store, it has no warnings on it, I caution everyone I know about these common UV lights.
These are UV lights, and they should be treated as such, and I am wondering if there should be stronger warnings about their use.

Attached Images

  • Attached Image: BlackLight_Sparticle_BP_Test.jpg

Edited by Cadmium, 10 November 2015 - 02:54.

#9 colinbm


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Posted 10 November 2015 - 02:00

But NO UV light is safe !
The SUN is NOT safe !
The disco / party lights are NOT safe, they are at a distance though & the atmosphere / distance, will cut some UV.

Safety has all levels of safe & danger !
Some happen immediately / instantly, so you are very aware.
Some have a time factor, minutes, hours, days....& lifespan limiting.
So because it doesn't happen immediately, why is there debate about how safe / unsafe, something is ?
Are the doubters that DUMB !
Why does it even need to be debated, it is a no brainer, DON'T FRIGGEN DO IT !

#10 Cadmium


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Posted 10 November 2015 - 03:09

Col, No debate, simply pointing out that I think common black lights may be more dangerous than commonly thought of by most people, and should carry warnings.
Those lights are used in all sorts of ways, close and far, and some people probably stare at them in close proximity. So no, I don't think they are 'safe'.

#11 colinbm


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Posted 10 November 2015 - 04:35

No offense intended Steve, I was responding to the thread in general & particularly the doubters ;-)

#12 JCDowdy


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Posted 10 November 2015 - 14:41

View PostCadmium, on 10 November 2015 - 03:09, said:

........ I think common black lights may be more dangerous than commonly thought of by most people, and should carry warnings.
Those lights are used in all sorts of ways, close and far, and some people probably stare at them in close proximity. So no, I don't think they are 'safe'.

A good question.

The safety standards have a classification scheme which includes an 'Exempt' class. As the name implies products in the 'Exempt' class are exempted from label warning requirements. This does not mean that an 'Exempt' source is totally without measureable 'Hazard', only that the probable 'Risk' from that 'Hazard' is deemed by competent authorities to be acceptable. In this context 'Hazard' is best understood as a source of potential injury and 'Risk" is the likelihood that exposure to a hazard will result in injury to a normal person.

The methods, in the testing standards I mentioned, specify measurement distances depending on the nature of and assumed use of a source. Misuse of a source, such as staring at a black light in close proximity, is therefore not the legal responsibility of the product manufacturer. A toothbrush manufacturer is likewise not responsible if you poke it in your eye.

The pertinent question must then be, is the use of a black light for UV photography an assumed, normal or predictable, use of the source? The black light you show above has a standard medium base which will fit the socket in an overhead room light or a free standing lamp of some sort. The presumed use is for the excitation of fluorescence in objects for aesthetic reasons, the stereotypical black light poster for example. However, the measurement required is 20 cm on a bare lamp. If you are closer and/or put that lamp in a reflector and/or use more than one bulb and then point it into someone's face you could exceed the assumed conditions of exposure which permitted the exemption from label warnings.

All of what I just said presumes a source was actually properly tested and that the jurisdiction in which it it was manufactured or sold is aware of or concerned about photobiological safety standards.

#13 Andrea B.

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Posted 10 November 2015 - 15:49

Col, while I appreciate your enthusiasm in getting the word out that UV light is dangerous, remember that not everyone actually knows that! So we must let the questions be asked and then provide a responsible answer. :)

Cadmium's question, for example, now prompts me to go into the Sticky and the first post and add a remark about the UV "party lights" which are so commonly used.
Andrea G. Blum
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#14 nfoto

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Posted 15 November 2015 - 19:37

We can only do so much in pointing out the inherent danger of dealing with UV light sources. Let's applaud Andrea for her efforts and hope people understand the need for protecting themselves. Enlightening and educating people assume there are senders and receivers of information.

#15 Pylon


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Posted 19 November 2015 - 03:29

I have contact lenses that say they are uv-blocking.

I took a shot of my eye using a UV flash attached to the hotshoe of my camera:

Attached Image: eye.JPG

Using contact lenses, do you think it is now safe to photograph people in UV with their eyes open?

I was also using the 199A and noticed that the power settings weren't really changing whenever I changed the right slider, or the slider that is tucked away when the flash is folded, on the front of the unit. It used to be that if the right slider was all the way down, it was at full power. Now it doesn't seem to be change.

Edited by Pylon, 19 November 2015 - 03:33.

#16 Andrea B.

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Posted 19 November 2015 - 15:38

Using contact lenses, do you think it is now safe to photograph people in UV with their eyes open?

That is an interesting question! I think that probably the answer is likely to be no unless you have very specific information about the brand and type of contact lenses. Here are 3 reasons why.
  • Not all contact lenses cover the entire pupil of the eye.
  • Not all contact lenses have UV blocking capability.
  • In contact lenses which do have some UV blocking, the amount varies.
Here is a reference from the American Optometric Association about contact lenses & UV protection: UV Protection with Contact Lenses

Additionally, UV light doesn't just harm the pupil/cornea/lens of the eye, UV can also harm the white area of the eye (called the conjunctiva) by causing pterygium, which are raised, pinkish lesions. The condition is sometimes called "Surfer's Eye". Pterygium can grow and eventually interfere with vision by pulling on the cornea or by covering part of the pupil. And big pterygium are really gross looking!!
UV can also cause other types of lesions on the eyelids or eye rim.

OK, get the picture now?

Yes, you finally got your UV eye picture above. There were no surprises. So stop UV flashing your eye so that I won't have to use you as the Bad Example in a couple of years when you are being rolled into the operating room for eye surgery.

All you really need to do is go outdoors in good sun and take a UV selfie. Much safer.

Why not go take some useful UV photographs of anything except living eyes and provide us with some interesting forensic examples? Please.
Andrea G. Blum
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#17 colinbm


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Posted 19 November 2015 - 22:30

UV light causes everything from sunburn to skin cancer and the wrinkles and sagging that come with age. But what exactly does it do in our bodies to wreak all that havoc?
Ultraviolet (UV) light is just a higher energy version of the light we see (visible light). And it's that higher energy that makes the UV in sunlight damaging to our cells and tissues.
To do any damage, UV light has to be absorbed. This happens at the molecular level. And it happens one electron at a time.
When a single electron absorbs a photon of UV light, that electron goes into a higher energy state. An excited electron like that makes a molecule behave in different ways — sticking to things it shouldn't stick to, changing shape, and generally messing with normal healthy cell business.
Luckily we evolved in a world that's saturated with UV light, so our cells have built-in repair kits for the damage UV radiation can do. But if the damage outweighs our capacity to repair, or our repair kits themselves get damaged, it's hello liver spots, cataracts and — way too often — skin cancer.
There are two kinds of UV radiation in sunlight — UVA and the higher energy UVB. And the trouble starts when they're absorbed by our more important molecules — DNA, RNA or proteins.
The pain. The heat. The redness. The judgemental looks from everyone who thought to dress appropriately.
They're all part of the sunburn experience. And — judgemental looks aside — they are all caused by UVB radiation.
Sunburn is the body's way of healing from the damage caused by UV radiation. It's your standard inflammation to clear away damaged cells, plus a little pain.
Like all inflammations, it involves a bunch of messenger chemicals (cytokines) signalling for more blood to be delivered (causing redness and heat) and more white blood cells to clean up the mess. And the whole thing can be kicked off by UV damage to a single molecule — a small bit of RNA called U1.
When a photon of UVB hits U1 RNA in the nucleus of a cell, it changes the RNA's structure. That tiny tweak is enough to kick off the whole heat-redness sunburn cytokine festival.
The pain part of sunburn is down to one particular messenger molecule, CXCL5. It attracts white blood cells into the skin's dermal layer, activating pain fibres there.
So it's CXCL5 that makes us sensitive to pain for a couple of days after the event, which has made it a 'molecule of interest' for pharmaceutical companies looking for new pain-relief drugs.
If you've had a skin cancer frozen off or cut out, you can blame kinky, mutant DNA caused by UVB light.
Somewhere back in your past, a photon of UVB made two bits of your DNA that are next to one another stick together (a couple of thymines, or 'T's in DNA code).
With those two T's stuck together, that stretch of DNA suddenly had a kink in it. Like a zipper with a broken tooth, the kink distorts the shape of the DNA in that cell, making it harder for your cell's enzymes to read and copy it properly.
Luckily we've got an entire molecular system devoted to finding and fixing these kinks. More than 30 proteins work together to replace the affected DNA. It's an incredible system, but it's not foolproof, so over time you can get a build-up of missed errors.
Errors in DNA are mutations, and if those mutations affect the cell's ability to keep itself in check (like a mutation in a tumour-suppressing gene), you can get the kind of out-of-control growth of cells that make up a skin cancer.
Worse still, if the mutation happens in a melanocyte (the skin cells containing the brown pigment melanin that colours our freckles, moles and tans) a far more dangerous cancer can result — melanoma.
Direct attacks on DNA aren't the only way UVB can cause mutations. It can also break proteins apart, and the high-energy molecules that result (radicals) are spectacular at attacking DNA.
UVA gets in on the act too by creating high-energy, oxygen-based compounds that go on a rampage, ripping other molecules apart.
Anti-oxidants in our cells do their best to soak up these destructive radicals, but it only takes one missed error in the wrong gene to need a date with your doctor and some liquid nitrogen.
The cloudy lens that makes it hard for cataract sufferers to see can also be caused by UV light.
The lens in your eye is normally clear, because the cells that make it up don't have a nucleus or other lumps to interfere with light — they mostly contain proteins, neatly aligned to let light through. But in 2014, researchers showed UVA light can trigger a chain reaction inside the lens that makes the proteins clump together, causing the cloudy look.
Our eyes have a special set of proteins, called chaperones, that work against the clumping, but if the clumping outperforms the chaperones, cloudy cataracts are the result.
While UVB is busy mutating DNA and setting off sunburn in the epidermis, UVA can penetrate more deeply into the dermis (the second layer of skin cells) where it converts firm, youthful skin to something that looks like mine.
Anyone who's spent more than $10 on a beauty product knows the key to firm skin is a protein called collagen. It comes in long fibres that form a mesh, giving structure to our flesh.
UVA doesn't directly attack the collagen, it's sneakier than that.
UVA activates receptors that produce the enemy of firm skin: matrix metalloproteinases. These enzymes have one job and they do it beautifully: breaking down collagen. And it doesn't take much UV at all to get this going, so even without sunburn any parts of your skin that are exposed to the sun will age.
As if the collagen attack wasn't insult enough, UV radiation also interferes with the production of Vitamin A receptors on our skin cells.
Vitamin A is critical for cell growth in our skin, but without functioning receptors for the vitamin to activate, our skin ends up thinning, and that's something no amount of carrots can fix.

#18 JCDowdy


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Posted 20 November 2015 - 15:38

Tiresome oversimplification and incorrect statements, MSN dot com is simply not a credible source.

#19 Andrea B.

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Posted 20 November 2015 - 16:57

It would be useful to know specific incorrect statements?

At least this MSN article does warn people of the UV dangers.
Andrea G. Blum
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#20 Alaun


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Posted 20 November 2015 - 17:40

the original is from ABC science, written by a Bernie Hobbs, and with " thanks to Assoc Prof Terry Walsh, Head of School - Biomedical Sciences, QUT":