Minimizing the negative effects of sun-derived UV radiation
October 3, 2014 8:38 AM   Subscribe

How long do I have to be exposed to 'bad UV' to be at risk of negative effects?

I live and work in the city, so although I'm often out and about while UV is at danger-high levels, I'm generally able to keep to the shadows. When I cross roads, however, I'm exposed to UV for brief periods (i.e. no more than 30 seconds). Question 1: Do I need to put on my hat and cover my arms for these brief periods? How much exposure does it take to be at risk of the negative effects associated with UV?

Question 2: If I sit outside, but in the shade when the UV is at its dangerous levels, do I need to worry about reflected radiation? Or is it only direct exposure (i.e. nothing but the atmosphere between me and the sun) I need to be concerned with?

I have fair and sensitive skin, and tend to burn rather than tan. But I don't like wearing hats and long sleeves if I don't have to. I generally take care of myself so that I don't burn, and make a point of getting 'good UV' exposure (for vitamin D) at appropriate times of the day; but I'm concerned about 'bad UV' exposure.
posted by paleyellowwithorange to Health & Fitness (6 answers total) 2 users marked this as a favorite
 
Any UV exposure - both does damage and triggers vitamin D production. There is no magic threshold above which you're horribly at risk and below which you're perfectly safe; also, everybody responds differently to UV.

Melanin (the chemical that darkens) is a UV absorbent, so people with naturally dark skin or even a basic tan suffer somewhat less damage from any given degree of UV exposure than paler folks. On the other hand, the very existence of a basic tan is evidence that a potentially damaging degree of UV exposure has already taken place; tanning is first-stage sunburn, and even the crappiest commercial sunscreen slapped on without proper care and attention provides way more protection than the tan does.

The trick is not doing damage at a greater rate than you can repair, and the easiest way to monitor that is by paying attention to your skin. If you're not burning and you're not tanning and your vitamin D levels are OK, you're doing it right. And if your 30-second exposures are not adding up to more than a few minutes of total exposure, I would be surprised to see you get a burn off them.

Even so, it pays to go and get a periodic once-over for skin cancers from somebody who knows what they're doing.
posted by flabdablet at 9:29 AM on October 3, 2014


Q1: The (conservative, not proven but widely accepted) model for cancer risk from ionizing radiation is the linear no threshhold model (LNT). Some looking shows it is generally accepted for UV exposure as well. LNT holds that small doses are as proportionately harmful as larger doses. There is no safe dose, any exposure to sunlight/UV light has an associated risk of cancer.

Q2: UV light can be reflected. For your purposes, you can probably assume UV light is reflected like regular light. Snow will reflect it particularly well. Dirt not so much. Mirrors yes, blacktop or concrete not so much.

Unsolicited advice: You are probably doing just fine by being concious of the hazard and wearing hats and long sleaves. I don't think doing anything else is practical or desirable. Risk is everywhere, keep things in perspective, and don't let it affect you too much.
posted by pseudonick at 9:52 AM on October 3, 2014


The easiest way to address this is to apply a daily moisturizer with an SPF to your face and forearms, rather than worry about shading those parts of your body during various short exposures throughout the day. I use one from Burt's Bees that has a zinc-oxide based sunscreen rather than the usual stuff like avobenzone (which isn't exactly proven to be dangerous but still sketches me out a little if I'm putting it on my skin regularly).

If you are in the shade you don't need to worry. Whatever is shading you (tree foliage or whatever) has at least as high an SPF as clothing. if there were light reflecting on you, you wouldn't be in shadow. Reflection is a concern when you are in the water or out on a snowy day in the sun.

flabdablet's advice about getting skin checks is particularly good if you have a family history of skin cancer or if you have moles/freckles.
posted by treehorn+bunny at 9:58 AM on October 3, 2014 [2 favorites]


My background is northern european, and I live in southern california so I've always been very careful about sun exposure. Nonetheless, three years ago, I had a basal cell carcinoma (BCC) surgically removed. BCC typically doesn't appear until your 70's, so I'm ahead of schedule . My dermatologist advised, that with my skin type, I need to be fanatical about sun exposure. She stressed that sand and concrete absolutely do reflect UV, and wearing protection from above is no help: typical scenario, where you are walking along the concrete sidewalk on a sunny day, you're wearing a hat and clothing so no light hits your skin directly from above - but the UV reflected off the pavement is hitting your face, and unless you have some kind of protection, you are getting exposure. My wife who is also of a similar background, routinely puts on some kind of light powder/makup thingie with UV protection built in, and that's the only way in which she goes out. If you are of a similarly unlucky skin type, you really must take measures others would laugh at. Melanoma is no fun. Also, the dermatologist claims that UV damage is cumulative, so any small exposures add up. Of course, there are things you can do to minimize the damage. For example, it has been shown that consuming coffee or green tea before UV exposure during exercise, strongly diminishes the negative UV effects. Carotenoids and various bioactive molecules from fruits and vegetables protect the skin from UV (to a degree). If you have minimal sun exposure you're vulnerable to vit. D deficiencies (it's hard to get it all from the diet), so you should have your vit. D status measured and supplement with D3 if necessary. And with your skin type (assuming its vulnerable), visits to a dermatologist are a yearly or even bi-annual (if anything is found) necessity.
posted by VikingSword at 11:13 AM on October 3, 2014 [1 favorite]


The coffee connection:

Harvard study shows coffee consumption inversely associated with risk of most common form of skin cancer

General herb and skin UV:

Potential of herbs in skin protection from ultraviolet radiation [PMID: 22279374]

Note: these are no panacea and no substitute for adequate UV protection measures. I'm a regular coffee and green tea drinker, and I consume above average amount of fruits and vegetables, and I'm careful about sun exposure and I still got BCC.
posted by VikingSword at 11:29 AM on October 3, 2014


BCC typically doesn't appear until your 70's, so I'm ahead of schedule .

By that measure, so are a lot of us. (I wonder if the 70s rule of thumb is from pre-ozone layer depletion times?) Anecdotal, but I and some of my 50-something fair-skinned relatives and friends are having to have BCCs removed. (I had a quarter-sized BCC patch removed last month.)

My sense is much of the damage now showing up as BCC was actually done to my back and shoulders in the 70s and 80s (my teens and 20s), before sunscreen was promoted so vigorously by health authorities, and occasional blistering sunburns were of course painful for a day or two but not considered a long-term health risk.

Use high-SPF sunscreen daily / regularly, not just when doing outdoor activities in direct sunlight (I use 30 on regular/work days, and 50 when working in the yard, reapplied if sweating a lot or out there for more than a couple hours). If you're fair-skinned, light- or red-haired, non-brown-eyed, or have freckles, be especially diligent about using 30+ SPF daily (in the winter too) and consider regular visits to a dermatologist. As far as Vitamin D goes, most doctors these days consider it more important to protect your skin against cancer risks than worry about maximizing sun-related Vitamin D production -- you can also get D from fortified milk & OJ, and many kinds of fish (like salmon) or portobellos if you're vegetarian, and of course, vitamin supplements.
posted by aught at 6:37 AM on June 4, 2015


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